Low-dimensional metal-halide perovskites for infrared, tetrahertz, and millimeter-wave light detection

Abstract

The present invention provides devices for detecting mid-infrared (MIR) light.

Description

[0001] TITLE OF THE INVENTION LOW-DIMENSIONAL METAL-HALIDE PEROVSKITES FOR INFRARED, TETRAHERTZ, AND MILLIMETER- WAVE LIGHT DETECTION

[0002] CROSS-REFERENCE TO RELATED APPLICATIONS

[0003] This application claims priority to U.S. Provisional Application No. 63 / 581,884, filed September 11, 2023, the disclosure of which is incorporated by reference herein in its entirety.

[0004] BACKGROUND OF THE INVENTION

[0005] The mid-infrared (MIR) wavelength range, encompassing both mid-wave infrared (MWIR, 3~5 pm) and long-wave infrared (LWIR, 8—14 pm), is technologically important for gas and molecular sensing, bio-imaging, environmental monitoring, free-space communication, and thermal energy harvesting (Muraview, A. V., et al., 2018, Nature Photonics, 12:209-214; Lin, H., et al., 2013, Optics Letters, 38: 1470-1472; Petersen, C. R., et al., 2018, Optics Letters, 43:999-1002; Garaba, S. P., et al., 2018, Environmental Science & Technology, 52: 11699- 11707; Zou, K., et al., 2022, Nature Communications, 13:7662; McSherry, S., et al., 2022, Nature Nanotechnology, 17: 1104-1110)). In comparison to the detection of visible and nearinfrared light, MIR light-detection is much more challenging due to the small photon energies. Cryogenic cooling is often required for MIR “photon” detectors built from small-bandgap semiconductors, which increases the device size, weight, cost, and failure rate (Bhan, R. K., and Dhar, V., 2019, Opto-Electronics Review, 27:174-193; Rogalski, A., 2005, Reports on Progress in Physics, 68:2267-2336). MIR “thermal” detectors, also known as bolometers, can operate at ambient temperature at a sacrificed bandwidth (Yadav, P. V. K., et al., 2022, Sensors and Actuators A: Physical, 342: 113611). Bolometers consist of a MIR light-absorbing material in close contact with a temperature-sensitive resistive element, the latter usually made of vanadium oxide (VOx with x = 1.8~2). Suspended structures are typically employed in bolometers for reducing thermal conductance between the heat-sensitive element and the support substrate (Wang, H., et al., 2004, Infrared Physics & Technology, 45:53-57). Several new schemes of MIR detection have been recently demonstrated, which exploit strong coupling between molecular vibrations and plasmonic near-fields, ratiometric luminescent properties of rare earth ion-doped nanocrystals, and collective photo-response of charge density wave systems (Xomaliz, A., et al., 2021, Science, 374: 1268-1271 ; Liang, L., et al., 2022, Nature Photonics, 16:712-717; Wu, D., et al., 2018, Scientific Advances, 4:eaao3057).

[0006] Therefore, new material platforms are desirable for improving the speed and device scalability for MIR detection. The present invention addresses this unmet need.

[0007] SUMMARY OF THE INVENTION

[0008] In one aspect, the disclosure relates to a thin-layer device for detection of mid-infrared light (MIR) comprising a layer of a metal halide perovskite (MHP) film on a layer of a low- thermal conductivity polymer or a thin inorganic membrane. In some embodiments, the MHP comprises a lead halide and an ammonium salt. In some embodiments, the lead halide is selected from PbCb, PbBn, and Pbl2. In some embodiments, the ammonium salt is selected from the group consisting of MeNHsCl, MeNH3Br, MeNH3I, EtNH3Cl, EtNHsBr, EtNH3I, n-PrNHsCl, n- PrNH Br. n-PrNHiI, i-PrNEHCl, i-PrNH3Br, i-PrNEEI, n-BuNHiCl, n-BuNHiBr, n-BuNEbl, i- BuNHsCl, i-BuNH3Br, i-BuNH3I, S-BUNH3C1, s-BuNH3Br, s-BuNH3I, t-BuNHsCl, t-BuNH3Br, t-BuNH3I, PhCH2NH3Cl, PhCH2NH3Br, PhCH2NH3I, PhCH2CH2NH3Cl, PhCH2CH2NH3Br, PhCH2CH2NH3I, PhCH2CH2CH2NH3Cl, PhCH2CH2CH2NH3Br, and PhCH2CH2CH2NH3I. In some embodiments, the MHP is (PhCH2CH2NH3)2Pbl4 ((PEA)2Pbl4).

[0009] In some embodiments, the low-thermal conductivity polymer has a thermal conductivity less than about 0.25 W m’1K'1. In some embodiments, the low-thermal conductivity polymer is one or more selected from the group consisting of nylon-6 (PA6), polyetheretherketone (PEEK), polytetrafluoroethylene (PTFE), poly (dimethyl siloxane) (PDMS), polysulfone (PSU), polymethylmethacrylate (PMMA), polycarbonate (PC), polyvinylchloride (PVC), polyvinylidene difluoride (PVDF), polyethylene terephthalate (PET), polystyrene (PS), polypropylene (PP), polyethylene (PE), and polyimide (PI). In some embodiments, the low-thermal conductivity polymer is PET.

[0010] In some embodiments, the low-thermal conductivity polymer is PET and the MHP is (PhCH2CH2NH3)2PbI4.

[0011] In some embodiments, the thickness of the MHP layer is between about 100 nm and about 10,000 nm. In some embodiments, the thickness of the MHP layer is between about 500 nm and about 1,000 nm. In some embodiments, the thickness of the MHP layer is about 940 nm. In some embodiments, the device further comprises a layer of infrared-absorbing nanocrystals on the MHP face opposite the PET. In some embodiments, the infrared-absorbing nanocrystals comprise cadmium oxide (CdO). In some embodiments, the infrared-absorbing nanocrystals further comprise one or more dopants selected from the group consisting of indium, fluorine, gold, silver, and aluminum. In some embodiments, the thickness of the layer of infrared-absorbing nanocrystals is between about 100 nm and about 300 nm. In some embodiments, the thickness of the layer of infrared-absorbing nanocrystals is about 150 nm.

[0012] In some embodiments, the device further comprises a layer of aluminum oxide (AI2O3) between the MHP and the infrared-absorbing nanocrystals.

[0013] BRIEF DESCRIPTION OF THE DRAWINGS

[0014] The following detailed description of preferred embodiments of the invention will be better understood when read in conjunction with the appended drawings. For the purpose of illustrating the invention, there are shown in the drawings embodiments which are presently preferred. It should be understood, however, that the invention is not limited to the precise arrangements and instrumentalities of the embodiments shown in the drawings.

[0015] Figure 1, comprising Figure 1 A through Figure IF, depicts representative experimental results demonstrating the temperature coefficient of reflectivity (TCR) and thermal transport properties of di(phenylethylammonium) lead (II) iodide, (PEA)2Pbl4, (abbreviated as PEA). Figure 1A depicts representative temperature-dependent reflectance spectra of PEA single crystal. Figure IB depicts representative temperature-dependent TCR at the reflectance dipwavelength for PEA single crystal and spin-coated film. Figure 1C depicts representative temperature-dependent reflectance spectra of a spin-coated PEA film with ~1 pm thickness. Figure ID depicts representative time-integrated difference between normalized differential change in reflectance (denoted as AR / R) at 500 nm from infrared-pump visible-probe (IPVP) experiments and normalized change in the temperature of PEA (denoted as AT) from finite- element simulations, shown as a function of thermal conductivity (denoted as K) of PEA and interfacial thermal conductance between the PEA and silicon substrate (abbreviated as G). The differential change in reflectance, AR / R, is defined as [R(t) — (0)] / R (0), with R(0) being reflectivity prior to pump excitation and R(t) being reflectivity at delay time t after pump excitation. Figure IE depicts representative decay kinetics of AR / R at 500 nm and the fitted decay of AT with finite-element simulations. Figure IF depicts a representative transient spectral map of AR / R for a 940 nm-thick PEA film on PET measured at room temperature (pump wavelength: 3170 nm; fluence: 3.6 mJ cm’2).

[0016] Figure 2, comprising Figure 2A through Figure 2D, depicts representative experimental and theoretical optical properties of PEA. Figure 2A depicts a representative reflectance spectrum of single-crystal PEA at room temperature (blue) and a calculated reflectance spectrum of PEA, with the relative permittivity described by the Lorentzian oscillator s(to) = + £c°=5-07 is the high-frequency permittivity, mL= 2.39 eV is the exciton energy, y = 67 meV is the exciton damping factor, and AL= 1.15 eV is the oscillator strength. Figure 2B depicts representative complex refractive indices of PEA calculated from the Lorentzian oscillator model. Figure 2C depicts representative complex relative permittivity of PEA calculated from the Lorentzian oscillator model. Figure 2D depicts representative calculated optical penetration depth, calculated as 1 / cr; a is the absorption coefficient determined as a = 2ns"

[0017] — — (E" is the imaginary part of relative permittivity, n is the real part of refractive index, and TL is the wavelength). The optical penetration depth is equivalent to the depth at which the light intensity drops to 1 / e of the original intensity.

[0018] Figure 3 depicts representative experimental results demonstrating that maximal TCR varies with temperature due to the spectral shift of the reflectance dip. The x-axis represents the temperature-dependent wavelength at which single-crystal PEA exhibits the largest TCR. The y- axis represents the TCR values at the corresponding wavelength.

[0019] Figure 4, comprising Figure 4A and Figure 4B, depicts representative X-ray diffraction patterns of spin-coated PEA films. Figure 4A depicts a representative X-ray diffraction pattern of spin-coated PEA on a glass substrate. Figure 4B depicts a representative X-ray diffraction pattern of spin-coated PEA on a polyethylene terephthalate (PET) substrate.

[0020] Figure 5 depicts a representative transient spectral map of AR / R for 640 nm-thick spin- coated PEA film on Si measured at room temperature (pump wavelength = 3170 nm; pump fluence = 3.6 mJ cm"2).

[0021] Figure 6, comprising Figure 6A through Figure 6C, depicts representative experimental results demonstrating the properties of various indium-doped cadmium oxides (ICOs). Figure 6A depicts representative infrared absorbance spectra of ICO-1 nanocrystals, ICO-2 nanocrystals, and fluorine-doped ICO (FICO). Figure 6B depicts a representative transmission electron microscopy image of ICO-1 nanocrystals at 60,000* magnification, showing the uniform size distribution of the nanocrystals. Scale bar = 100 nm. Figure 6C depicts a representative scanning electron microscopy image showing the morphology of spin-coated ICO-2 nanocrystals on PEA / PET. Scale bar = 500 nm.

[0022] Figure 7, comprising Figure 7A through Figure 7H, depicts representative experimental results demonstrating the optical and structural properties of PEA films coated with ICO nanocrystals (NCs). Figure 7A depicts representative MIR transmittance spectra of ICO NC films with different doping concentrations on sapphire substrates. Figure 7B depicts representative cross-sectional scanning electron microscopy image of ICO-1 / PEA / PET (Scale bar = 1 pm) and its XRD pattern (the out-of-plane XRD peaks of PEA are indexed). Figure 7C depicts representative MIR transmission spectra of CaF substrate-supported PEA films with and without ICO NC films on top. Figure 7D depicts a representative transient AR / R spectral map of ICO-l / PEA / PET at room temperature (pump wavelength = 3170 nm; fluence = 3.9 mJ- cm'2). Figure 7E depicts representative differences in AR / R kinetics at 500 nm between PEA / PET and ICO-l / PEA / PET. Figure 7F depicts representative simulated decays of temperature (AT) for PEA (averaged for the top 140 nm, the probe penetration depth) in ICO-l / PEA / PET, obtained with various values of thermal conductivity (K) for the ICO-1. Figure 7G depicts a representative transient AR / R spectrum at 100 ns taken from 7D. Figure 7H depicts representative AR / R kinetics at 500 nm and its bi-exponential fit from Figure 7D.

[0023] Figure 8, comprising Figure 8A and Figure 8B, depicts representative spectral maps of PEA on PET with or without ICO-1. Figure 8A depicts a representative transient AR / R spectral map for a 940 nm-thick PEA film on PET at room temperature (pump wavelength = 3170 nm; fluence = 3.6 mJ cm'2). Figure 8B depicts a representative transient R / R spectral map of ICO- l / PEA / PET at room temperature (pump wavelength: 3170 nm; fluence: 3.9 mJ cm'2).

[0024] Figure 9, comprising Figure 9A through Figure 9D, depicts representative experimental results of PEA film on silicon (Si). Figure 9A depicts a representative transient R / R spectral map for ICO-l / PEA / Si on the microsecond (ps) time scale measured at room temperature. Figure 9A depicts a representative transient AR / R spectral map for ICO-l / PEA / Si on the nanosecond (ns) time scale measured at room temperature. Figure 9C depicts a representative transient AR / R spectral maps for PEA / Si measured at room temperature. Figure 9D depicts a representative comparison of the AR / R kinetics of the ICO-l / PEA / Si and the PEA / Si samples at 502 nm.

[0025] Figure 10 depicts representative simulated temperature profiles of an ICO / PEA / PET stack at various delay times following impulsive thermal excitation of the ICO film at time zero, showing energy transfer from the ICO to the PEA.

[0026] Figure 11, comprising Figure 11A through Figure 1 IE, depicts representative experiments on spectrally tunable, all-optical MIR photodetection using ICO / PEA / PET stacks. Figure 11A depicts a schematic representation of the all-optical MIR photodetection setup; BP1 (BP2) is the bandpass filter for the visible probe (the MIR pump). Figure 1 IB depicts representative lock-in voltage measured for PEA / PET coated with the three different ICO-NC films; data for PEA / Si coated with ICO-1 measured at the same MIR power density is also shown for comparison. Figure 11C depicts representative lock-in voltage of ICO-1 / PEA / PET as a function of the chopper frequency. Figure 1 ID depicts representative finite-element simulated decays of the temperature averaged over the probe penetration depth (140 nm) of a 940-nm thick PEA film deposited on Si and PET substrates. Figure HE depicts representative lock-in voltage of ICO-1 / PEA / PET versus the MIR power density (inset shows the data at 0 to 4 nW- pm’2).

[0027] Figure 12 depicts representative transmittance spectra of five MIR bandpass filters used in the MIR detection experiments (FB1900-200, FB3250-500, FB333O-15O, FB3750-500, and FB4000-500, from short to long wavelength) measured with FTIR.

[0028] Figure 13 depicts representative infrared absorbance spectra for a bare PET substrate as well as PET substrates coated with PEA / AI2O3 and terminated with thin films of the three types of ICO nanocrystals. The enhanced absorption from the nanocrystal films is indicated by the black arrows.

[0029] Figure 14, comprising Figure 14A through Figure 14D, depicts representative lock-in voltages measured as functions of the incident power of MIR source used in the all-optical MIR detection experiments with different ICO NCs. Figure 14A depicts representative lock-in voltage for a FICO / PEA / PET substrate. Figure 14B depicts representative lock-in voltage for an ICO- 1 / PEA / PET substrate. Figure 14C depicts representative lock-in voltage for an ICO-2 / PEA / PET substrate. Figure 14D depicts representative lock-in voltage for an ICO-l / PEA / Si substrate. Note the lower signal-to-noise ratio in Figure 14D relative to Figure 14A through Figure 14C. For Figure 14A through Figure 14D, the magnitude of MIR for different wavelengths were separately normalized.

[0030] Figure 15, comprising Figure 15A through Figure 15C, depicts representative results demonstrating thin membrane-based structures exhibiting <100 pW pm’2sensitivity. Figure 15A depicts a schematic illustration of the PEA / SiNx / ICO- l membrane structure supported by a Si substrate (Left: 3D illustration; Right: 2D view). Figure 15B depicts representative transient AR / R spectra of a floating PEA membrane for varying delay times (100 ps to 1.3 ms). Figure 15C depicts representative lock-in voltage of PEA / SiN.7ICO- l on Si versus MIR (3.33 pm) power density (inset shows the range from 0 to 300 pW- pm’2).

[0031] Figure 16 depicts a schematic illustration for a fabrication procedure for the two types of membrane-based structures: PEA / SiNx / ICO used in Figure 15, and ICO / PEA / SiN.. used in Figure 17.

[0032] Figure 17, comprising Figure 17A through Figure 17F, depicts representative experimental results demonstrating a thin membrane-based structure incorporating a dielectric coating enables <10 pW pm’2sensitivity. Figure 17A depicts representative results demonstrating the dielectric coating-induced decrease in reflectance near the excitonic resonance of PEA. Figure 17B depicts a representative transfer matrix-calculated reflectance spectra of PEA film covered by SiNx (refractive index n = 2.19) with SiN thickness varied from 0 to 300 nm. Figure 17C depicts a representative color-coded map of / ?y=67 mev plotted as a function of wavelength and SiNx thickness. Here, y = 67 meV is the fitted Lorentzian damping factor for PEA at ambient temperature (Figure 2) and, without the loss of generality, the increase of y from 67 to 77 meV is assumed to be induced by MIR light irradiation. Figure 17D depicts a schematic drawing of a representative inverted ICO / PEA / SiNx structure on Si substrate and the associated measurement scheme (Left: 3D illustration; Right: 2D view). Figure 17E depicts representative reflectance spectra for PEA covered with a 265-nm thick SiNx (calculated: dashed; measured: solid) and for PEA without any SiNx coverage (red, taken from data in Figure 1C). The measured lock-in voltage as a function of probe wavelength is shown in yellow for a PEA covered with a 265-nm thick SiNx. Figure 17F depicts representative lock-in voltage of ICO-l / PEA / SiNx versus MIR (3.33 pm in wavelength) power density (inset shows the range from 0 to 35 pW pm’2). Figure 18, comprising Figure 18A through Figure 18C, depicts representative results of long-wave infrared (LWIR) detection at 10.6 pm wavelength. Figure 18A depicts representative experimental transmittance, experimental reflectance, and calculated absorption for a 265-nm thick SiN.v membrane from 5 to 15 pm (left) and a schematic drawing of the sample and measurement configuration. Figure 18B depicts representative lock-in voltage of PEA / SiNv versus MIR (10.6 pm in wavelength) power density (inset shows the range from 0 to 300 pW pm'2). Figure 18C depicts representative maximum AR / R as a function of the thickness of the SiN.v layer on top of PEA, and the associated full-width-half-maximum of the peak of AR / R.

[0033] Figure 19, comprising Figure 19A through Figure 19F, depicts representative transient R / R spectral maps for a single-crystal PEA measured at various temperatures. Figure 19A depicts a representative spectral map for single-crystal PEA at 80 K. Figure 19B depicts a representative spectral map for single-crystal PEA at 130 K. Figure 19C depicts a representative spectral map for single-crystal PEA at 170 K. Figure 19D depicts a representative spectral map for single-crystal PEA at 210 K. Figure 19E depicts a representative spectral map for singlecrystal PEA at 250 K. Figure 19F depicts a representative spectral map for single-crystal PEA at 290 K. For Figure 19A through Figure 19E, pump wavelength = 3170 nm; fluence = 2.3 mJ- cm'2).

[0034] Figure 20, comprising Figure 20A through Figure 20C, depicts representative AR / R kinetics measured for PEA / PET. Figure 20A depicts a representative temperature dependence of AR / R kinetics of 940 nm PEA on PET for the wavelength of maximum AR / R at each temperature. Figure 20B depicts a normalized plot of the data shown in Figure 20A. Figure 20C depicts representative temperature-dependent AR / R spectra at 10 ns delay time for a PEA single crystal pumped at 3170 nm at fluence of 2.2 mJ cm'2.

[0035] Figure 21, comprising Figure 21 A and Figure 21B, depicts representative AR / R on PEA- on-Si substrate. Figure 21 A depicts a representative pump fluence-dependent AR / R for a 640 nm-thick PEA on Si substrate measured at room temperature with a pump wavelength of 3170 nm. Figure 21B depicts normalized AR / R from Figure 21A normalized.

[0036] Figure 22, comprising Figure 22A and Figure 22B, depicts representative experimental results for MIR imaging. Figure 22A depicts a schematic representation of an MIR imaging experiment with a pump wavelength of 3.3 pm. Figure 22B depicts representative images of a PEA film covered by ITO by brightfield reflective imaging (left) and by R / R probed using monochromatic light (right; the region covered by ITO can block the MIR pump light).

[0037] Figure 23 depicts a representative infrared transmission spectrum of sputtered ITO film on glass, which was used as a shadow mask in Figure 22F.

[0038] Figure 24, comprising Figure 24A through Figure 24C, depicts representative temperature decay profiles. Figure 24A depicts representative temperature decay rates of the center of a suspended Si pad, a (PEA)2Pbl4 film on PET, and a floating (PEA)2Pbl4 membrane (1 pm thick). All three structures are subjected to an impulsive temperature rise of 1 K at t = 0. Figure 24B depicts representative snapshots of temperature profiles for a floating (PEA)2Pbl4 membrane at various delay times after t = 0. Figure 24C depicts a representative accumulative temperature rise at the center of the floating (PEA)2Pbl4 membrane subjected to continuous MIR illuminations with two different incident power densities. For Figure 24A through Figure 24C, the MIR beam is Gaussian-like with a radius us 10 pm.

[0039] Figure 25, comprising Figure 25A and Figure 25B, depicts representative heat dissipation with various MIR beam radii. Figure 25 A depicts representative temperature decay rates of the center of a floating (PEA)2Pbl4 membrane with impulsive excitation by MIR pulse with different beam radii. Figure 25A depicts representative temperature decay rates shown in Figure 25B normalized by the 10 pm radius data, suggesting an order of magnitude increase when spot radius goes from 10 pm to 50 pm.

[0040] Figure 26 depicts a schematic representation of the dielectric coating on a (PEA)2Pbl4 membrane and its impact on the reflectance spectra of (PEA)2Pbl4 near its exciton resonance.

[0041] Figure 27, comprising Figure 27A through Figure 27D, depicts representative calculated properties of (PEA)2Pbl4. Figure 27A depicts a representative calculated reflectance spectra of (PEA)2Pbl4 coated with a dielectric with refractive index n = 1.73 and thickness varied from 0 to 250 nm. Figure 27B depicts a representative color-coded map of AR / R, defined as AR / R=(RY=77 mev - R7=67mev) / Ry=67mev. y=67 meV is the fitted Lorentzian dampening factor for (PEA)2Pbl4 at ambient temperature, and the increase of y from 67 meV to 77 meV is caused by MIR-induced temperature rise. The dielectric layer has n - 1.73 and thickness varied from 0 to 250 nm. Figure 27C depicts the AR / R taken from Figure 27B for selected coating thicknesses. Figure 27D depicts a representative enhancement spectra of AR / R. Figure 28, comprising Figure 28 A and Figure 28B, depicts representative properties of MIR detectors. Figure 28A depicts a schematic representation of a (PEA)2Pbl4 membrane-based MIR detector. Figure 28B depicts representative plasma frequency dependence of MIR absorption spectrum for a TCO film with 200 nm thickness and y = 20 meV.

[0042] Figure 29 depicts a schematic representation of the PEEL process for fabricating large- area, periodic gold bowtie nano-antennas on (PEA)2Pbl4 membranes.

[0043] Figure 30 depicts a representative FDTD-simulated MIR absorption spectra of gold bowtie antennas.

[0044] Figure 31 depicts schematic representations of various exemplary MHP-based MIR detection devices.

[0045] DETAILED DESCRIPTION

[0046] The present invention relates to devices for detecting mid-infrared (MIR) light. In some embodiments, devices of the invention are thin-layer “2-dimensional” (2D) devices. In some embodiments, devices of the invention comprise a layer of a metal halide perovskite (MHP) on a low-thermal conductivity substrate or on a thin floating-membrane support. In some embodiments, the MHP is a lead halide perovskite. In some embodiments, the lead halide perovskite is a lead iodide perovskite. In some embodiments, the lead halide perovskite comprises an ammonium ligand. In some embodiments, the ammonium ligand is a phenylethylammonium salt. In some embodiments, the MHP is di(phenylethylammonium) lead (II) iodide.

[0047] In some embodiments, the low-thermal conductivity substrate has a thermal conductivity less than about 0.25 W m’1K'1. In some embodiments, the low-thermal conductivity substrate is a polymer. In some embodiments, the low-thermal conductivity substrate is polyethylene terephthalate (PET).

[0048] In some embodiments, devices of the present invention further comprise a layer on the MHP opposite to the low-thermal conductivity substrate to improve the absorption of MIR light. In some embodiments, the layer to improve the absorption of MIR light is a layer of nanocrystals (NCs). In some embodiments, the NCs comprise cadmium oxide (CdO). In some embodiments, the CdO is doped with one or more additional compounds. In some embodiments, the CdO is doped with iridium, fluorine, gold, silver, and / or aluminum. In some embodiments, the device further comprises a layer of aluminum oxide (AI2O3) between the MHP layer and the NC layer.

[0049] Definitions

[0050] Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the invention pertains. Although any methods and materials similar or equivalent to those described herein can be used in the practice for testing of the present invention, exemplary materials and methods are described herein. In describing and claiming the present invention, the following terminology will be used.

[0051] It is also to be understood that the terminology used herein is for the purpose of describing particular embodiments only, and is not intended to be limiting.

[0052] The articles “a” and “an” are used herein to refer to one or to more than one (i.e., to at least one) of the grammatical object of the article. By way of example, “an element” means one element or more than one element.

[0053] “About” as used herein when referring to a measurable value such as an amount, a temporal duration, and the like, is meant to encompass variations of ±20%, ±10%, ±5%, ±1%, or ±0.1% from the specified value, as such variations are appropriate.

[0054] As used herein, the term “alkyl,” by itself or as part of another substituent means, unless otherwise stated, a straight or branched chain hydrocarbon having the number of carbon atoms designated (i.e. C1-6 means one to six carbon atoms) and including straight, branched chain, or cyclic substituent groups. Examples include methyl, ethyl, propyl, isopropyl, butyl, isobutyl, tert-butyl, pentyl, neopentyl, hexyl, and cyclopropylmethyl.

[0055] As used herein, the term “substituted alkyl” means alkyl as defined above, substituted by one, two or three substituents selected from the group consisting of halogen, -OH, alkoxy, -NH2, amino, azido, -N(CH3)2, -C(=O)OH, trifluoromethyl, -C=N, -C(=O)O(Ci-C4)alkyl, -C(=O)NH2, - SO2NH2, -C(=NH)NH2, and -NO2. Examples of substituted alkyls include, but are not limited to, 2,2-difluoropropyl, 2-carboxycyclopentyl and 3 -chloropropyl.

[0056] As used herein, the term “heteroalkyl” by itself or in combination with another term means, unless otherwise stated, a stable straight or branched chain alkyl group consisting of the stated number of carbon atoms and one or two heteroatoms selected from the group consisting of O, N, and S, and wherein the nitrogen and sulfur atoms may be optionally oxidized and the nitrogen heteroatom may be optionally quatemized. The heteroatom(s) may be placed at any position of the heteroalkyl group, including between the rest of the heteroalkyl group and the fragment to which it is attached, as well as attached to the most distal carbon atom in the heteroalkyl group. Examples include: -O-CH2-CH2-CH3, -CH2-CH2-CH2-OH, -CH2-CH2-NH-CH3, -CH2-S-CH2-CH3, and -CH2CH2-S(=O)-CH3. Up to two heteroatoms may be consecutive, such as, for example, -CH2-NH-OCH3, or -CH2-CH2-S-S-CH3.

[0057] As used herein, the term “alkoxy” employed alone or in combination with other terms means, unless otherwise stated, an alkyl group having the designated number of carbon atoms, as defined above, connected to the rest of the molecule via an oxygen atom, such as, for example, methoxy, ethoxy, 1-propoxy, 2-propoxy (isopropoxy) and the higher homologs and isomers.

[0058] As used herein, the term “halo” or “halogen” alone or as part of another substituent means, unless otherwise stated, a fluorine, chlorine, bromine, or iodine atom.

[0059] As used herein, the term “cycloalkyl” refers to a mono cyclic or polycyclic non-aromatic radical, wherein each of the atoms forming the ring (i.e. skeletal atoms) is a carbon atom. In one embodiment, the cycloalkyl group is saturated or partially unsaturated. In another embodiment, the cycloalkyl group is fused with an aromatic ring. Cycloalkyl groups include groups having from 3 to 10 ring atoms. Illustrative examples of cycloalkyl groups include, but are not limited to, the following moieties:

[0060] Monocyclic cycloalkyls include, but are not limited to, cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, cycloheptyl, and cyclooctyl. Dicyclic cycloalkyls include, but are not limited to, tetrahydronaphthyl, indanyl, and tetrahydropentalene. Polycyclic cycloalkyls include adamantane and norbomane. The term cycloalkyl includes “unsaturated nonaromatic carbocyclyl” or “nonaromatic unsaturated carbocyclyl” groups, both of which refer to a nonaromatic carbocycle as defined herein, which contains at least one carbon double bond or one carbon triple bond.

[0061] As used herein, the term “heterocycloalkyl” or “heterocyclyl” refers to a heteroalicyclic group containing one to four ring heteroatoms each selected from O, S and N. In one embodiment, each heterocycloalkyl group has from 4 to 10 atoms in its ring system, with the proviso that the ring of said group does not contain two adjacent O or S atoms. In another embodiment, the heterocycloalkyl group is fused with an aromatic ring. In one embodiment, the nitrogen and sulfur heteroatoms may be optionally oxidized, and the nitrogen atom may be optionally quatemized. The heterocyclic system may be attached, unless otherwise stated, at any heteroatom or carbon atom that affords a stable structure. A heterocycle may be aromatic or nonaromatic in nature. In one embodiment, the heterocycle is a heteroaryl.

[0062] An example of a 3-membered heterocycloalkyl group includes, and is not limited to, aziridine. Examples of 4-membered heterocycloalkyl groups include, and are not limited to, azetidine and a beta lactam. Examples of 5-membered heterocycloalkyl groups include, and are not limited to, pyrrolidine, oxazolidine and thiazolidinedione. Examples of 6-membered heterocycloalkyl groups include, and are not limited to, piperidine, morpholine and piperazine. Other non-limiting examples of heterocycloalkyl groups are: Examples of non-aromatic heterocycles include monocyclic groups such as aziridine, oxirane, thiirane, azetidine, oxetane, thietane, pyrrolidine, pyrroline, pyrazolidine, imidazoline, dioxolane, sulfolane, 2, 3 -dihydrofuran, 2, 5 -dihydrofuran, tetrahydrofuran, thiophane, piperidine, 1,2,3,6-tetrahydropyridine, 1,4-dihydropyridine, piperazine, morpholine, thiomorpholine, pyran,

[0063] 2.3 -dihydropyran, tetrahydropyran, 1,4-dioxane, 1,3-dioxane, homopiperazine, homopiperidine,

[0064] 1.3-dioxepane, 4,7-dihydro-l,3-dioxepin, and hexamethyleneoxide.

[0065] As used herein, the term “aromatic” refers to a carbocycle or heterocycle with one or more polyunsaturated rings and having aromatic character, i.e. having (4n + 2) delocalized (pi) electrons, where n is an integer.

[0066] As used herein, the term “aryl,” employed alone or in combination with other terms, means, unless otherwise stated, a carbocyclic aromatic system containing one or more rings (typically one, two or three rings), wherein such rings may be attached together in a pendent manner, such as a biphenyl, or may be fused, such as naphthalene. Examples of aryl groups include phenyl, anthracyl, and naphthyl.

[0067] As used herein, the term “aryl-(Ci-C3)alkyl” means a functional group wherein a one- to three-carbon alkylene chain is attached to an aryl group, e.g., -CTECTE-phenyl. In one embodiment, aryl-(Ci-C3)alkyl is aryl-CTE- or aryl-CH(CH3)-. The term “substituted aryl-(Ci-C3)alkyl” means an aryl-(Ci-C3)alkyl functional group in which the aryl group is substituted. Similarly, the term “heteroaryl-(Ci-C3)alkyl” means a functional group wherein a one to three carbon alkylene chain is attached to a heteroaryl group, e.g., -CTEC -pyridyl. The term “substituted heteroaryl-(Ci-C3)alkyl” means a heteroaryl-(Ci-C3)alkyl functional group in which the heteroaryl group is substituted.

[0068] As used herein, the term “heteroaryl” or “heteroaromatic” refers to a heterocycle having aromatic character. A polycyclic heteroaryl may include one or more rings that are partially

[0069] saturated. Examples include the following moi eties:

[0070] Examples of heteroaryl groups also include pyridyl, pyrazinyl, pyrimidinyl (particularly 2- and 4-pyrimidinyl), pyridazinyl, thienyl, furyl, pyrrolyl (particularly 2-pyrrolyl), imidazolyl, thiazolyl, oxazolyl, pyrazolyl (particularly 3- and 5-pyrazolyl), isothiazolyl, 1,2,3-triazolyl,

[0071] 1.2.4-triazolyl, 1,3,4-triazolyl, tetrazolyl, 1,2,3-thiadiazolyl, 1,2,3-oxadiazolyl, 1,3,4-thiadiazolyl and 1,3,4-oxadiazolyl.

[0072] Examples of polycyclic heterocycles and heteroaryls include indolyl (particularly 3-, 4-, 5-, 6- and 7-indolyl), indolinyl, quinolyl, tetrahydroquinolyl, isoquinolyl (particularly 1- and 5-isoquinolyl), 1,2,3,4-tetrahydroisoquinolyl, cinnolinyl, quinoxalinyl (particularly 2- and 5-quinoxalinyl), quinazolinyl, phthalazinyl, 1,8-naphthyridinyl,

[0073] 1.4-benzodioxanyl, coumarin, dihydrocoumarin, 1,5-naphthyridinyl, benzofuryl (particularly 3-, 4-, 5-, 6- and 7-benzofuryl), 2,3-dihydrobenzofuryl, 1,2-benzisoxazolyl, benzothienyl (particularly 3-, 4-, 5-, 6-, and 7-benzothienyl), benzoxazolyl, benzothiazolyl (particularly

[0074] 2 -benzothiazolyl and 5-benzothiazolyl), purinyl, benzimidazolyl (particularly 2-benzimidazolyl), benzotriazolyl, thioxanthinyl, carbazolyl, carbolinyl, acridinyl, pyrrolizidinyl, and quinolizidinyl.

[0075] As used herein, the term “substituted” means that an atom or group of atoms has replaced hydrogen as the substituent attached to another group. The term “substituted” further refers to any level of substitution, namely mono-, di-, tri-, tetra-, or penta-substitution, where such substitution is permitted. The substituents are independently selected, and substitution may be at any chemically accessible position. In one embodiment, the substituents vary in number between one and four. In another embodiment, the substituents vary in number between one and three. In yet another embodiment, the substituents vary in number between one and two. As used herein, the term “optionally substituted” means that the referenced group may be substituted or unsubstituted. In one embodiment, the referenced group is optionally substituted with zero substituents, i.e., the referenced group is unsubstituted. In another embodiment, the referenced group is optionally substituted with one or more additional group(s) individually and independently selected from groups described herein.

[0076] In one embodiment, the substituents are independently selected from the group consisting of oxo, halogen, -CN, -NH2, -OH, -NH(CH3), -N(CH3)2, alkyl (including straight chain, branched and / or unsaturated alkyl), substituted or unsubstituted cycloalkyl, substituted or unsubstituted heterocycloalkyl, fluoro alkyl, substituted or unsubstituted heteroalkyl, substituted or unsubstituted alkoxy, fluoroalkoxy, -S-alkyl, S(=0)2alkyl, -C(=O)NH[substituted or unsubstituted alkyl, or substituted or unsubstituted phenyl], -C(=0)N[H or alkyl]2, - OC(=O)N[substituted or unsubstituted alkyl]2, -NHC(=O)NH[substituted or unsubstituted alkyl, or substituted or unsubstituted phenyl], -NHC(=O)alkyl, -N[substituted or unsubstituted alkyl]C(=O)[substituted or unsubstituted alkyl], -NHC(=O)[substituted or unsubstituted alkyl], - C(OH)[substituted or unsubstituted alkyl]2, and -C(NH2)[substituted or unsubstituted alkyl]2. In another embodiment, by way of example, an optional substituent is selected from oxo, fluorine, chlorine, bromine, iodine, -CN, -NH2, -OH, -NH(CH3), -N(CH3)2, -CH3, -CH2CH3, -CH(CH3)2, - CF3, -CH2CF3, -0CH3, -OCH2CH3, -OCH(CH3)2, -OCF3, - OCH2CF3, -S(=O)2-CH3, - C(=0)NH2, -C(=0)-NHCH3, -NHC(=0)NHCH3, -C(=O)CH3, -0N(0)2, and -C(=0)0H. In yet one embodiment, the substituents are independently selected from the group consisting of C1-6 alkyl, -OH, C1-6 alkoxy, halo, amino, acetamido, oxo and nitro. In yet another embodiment, the substituents are independently selected from the group consisting of C1-6 alkyl, C1-6 alkoxy, halo, acetamido, and nitro. As used herein, where a substituent is an alkyl or alkoxy group, the carbon chain may be branched, straight or cyclic.

[0077] Ranges: throughout this disclosure, various aspects of the invention can be presented in a range format. It should be understood that the description in range format is merely for convenience and brevity and should not be construed as an inflexible limitation on the scope of the invention. Accordingly, the description of a range should be considered to have specifically disclosed all the possible subranges as well as individual numerical values within that range. For example, description of a range such as from 1 to 6 should be considered to have specifically disclosed subranges such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6 etc., as well as individual numbers within that range, for example, 1, 2, 2.7, 3, 4, 5, 5.3, and 6. This applies regardless of the breadth of the range.

[0078] Description

[0079] The present invention provides thin-layer “2-dimensional” (2D) devices for detecting mid-infrared (MIR) light. In some embodiments, devices of the invention comprise a plurality of thin layers. In some embodiments, devices comprise, as a first layer, a substrate layer. In some embodiments, the substrate layer comprises a low-thermal conductivity substrate. In some embodiments, the low-thermal conductivity substrate has a thermal conductivity less than about 0.25 W m’1K’1. In some embodiments, the low-thermal conductivity substrate is a polymer. In some embodiments, the low-thermal conductivity substrate is polyethylene terephthalate (PET). In some embodiments, the substrate layer comprises an inorganic membrane.

[0080] In some embodiments, devices of the present invention comprise, as a second layer, a metal halide perovskite (MHP). In some embodiments, the MHP is a lead halide perovskite. In some embodiments, the lead halide perovskite is a lead iodide perovskite. In some embodiments, the lead halide perovskite comprises an organic ammonium ligand. In some embodiments, the organic ammonium ligand is a phenylethylammonium salt. In some embodiments, the MHP is di(phenylethylammonium) lead (II) iodide.

[0081] In some embodiments, devices of the present invention comprise, as a third layer, a barrier layer. In some embodiments, the barrier layer improves the stability of the MHP. In some embodiments, the barrier layer prevents dissolution of the MHP. In some embodiments, the barrier layer is MIR-transparent. In some embodiments, the barrier layer comprises aluminum oxide (AI2O3).

[0082] In some embodiments, devices of the present invention further comprise, as a fourth layer, an enhancement layer comprising a composition that aids in the absorption of MIR light. In some embodiments, the enhancement layer comprises a plurality of MIR-ab sorbing nanocrystals (NCs). In some embodiments, the NCs comprise cadmium oxide (CdO). In some embodiments, the CdO is doped with one or more additional compounds. In some embodiments, the CdO is doped with iridium and / or fluorine.

[0083] In some embodiments, devices of the present invention comprise a thin floating- membrane as a support of the MHP. In some embodiments, the thin floating-membrane comprises a silicon nitride layer grown on silicon wafers. In some embodiments, the MHP itself is in the form of a self-supported thin membrane without any external supporting substrate.

[0084] MIR Detector

[0085] Generally, the disclosed MIR detectors comprise a stack of layers configured for photodetection. In some embodiments, an MIR detector of the present invention comprises a stack of layers having at least a metal halide perovskite (MHP) layer. Each layer may be described as being disposed or positioned above or below another layer, and at least partially in contact with one or more of the other layers (e.g., at least partially in contact with one or more surfaces of another layer). In some embodiments, any of the layers may comprise windows, openings, pores and / or etchings at least partially extending through the layers from a first surface to a second surface of each layer (e.g., a top and bottom surface of each layer). In some embodiments, an MIR detector comprises a first substrate layer and a second MHP layer. In some embodiments, an MIR detector comprises a first substrate layer, a second MHP layer, and a third barrier layer. In some embodiments, an MIR detector comprises a first substrate layer, a second MHP layer, and a third enhancement layer. In some embodiments, an MIR detector comprises a first support layer, a second substrate layer, and a third MHP layer. In some embodiments, an MIR detector comprises a first substate layer, a second MHP layer, a third barrier layer, and a fourth enhancement layer. In some embodiments, an MIR detector comprises a first substrate layer, a second support layer, a third substrate layer, and a fourth MHP layer. In some embodiments, an MIR detector comprises a first substrate layer, a second support layer, a third substrate layer, a fourth MHP layer, and a fifth enhancement layer. In some embodiments, each layer may comprise one or more materials and have the same thickness, or a similar thickness, or different thicknesses as discussed herein. In some embodiments, the thickness of the enhancement layer is less than the thickness of the substrate layer.

[0086] In some embodiments, as seen in Figure 31, an MIR detector 100 of the present invention comprises an MHP layer 102 disposed above or contacting a first surface of a substrate layer 104. In some embodiments, substrate layer 104 is disposed or positioned above a support layer 106, which is disposed or positioned above a second substrate layer 108. In some embodiments, the second surface of substrate layer 104 contacts a first surface of a support layer 106, the second surface of support layer 106 at least partially contacts a second substrate layer 108. As seen in Figure 31, in some embodiments, an MIR detector 200 of the present invention comprises a MHP layer 202 positioned above or contacting a first surface of a substrate layer 204. In some embodiments, substrate layer 204 is positioned above a support layer 206. In some embodiments, the second surface of substrate layer 204 at least partially contacts a first surface of a support layer 206. In some embodiments, support layer 206 is positioned above or at least partially contacts a second substrate layer 208. In some embodiments, the second surface of support layer 206 at least partially contacts a first surface of second substrate layer 208. In some embodiments, at least one of support layer 206 and / or second substrate layer 208 comprise one or more windows, openings, or pores which at least partially expose a surface (e.g., the top surface) of first substrate layer 204.

[0087] As seen in Figure 31, in some embodiments, an MIR detector 300 of the present invention comprises an MHP layer 302 positioned above or at least partially contacting a substrate layer 304. In some embodiments, MHP layer 302 is positioned below or at least partially contacting an enhancement layer 301. In some embodiments, a first or top surface of MHP layer 302 at least partially contacts a second or bottom surface of enhancement layer 301. In some embodiments, a second or bottom surface of MHP layer 302 at least partially contacts a first surface of a substrate layer 304. In some embodiments, substrate layer 304 is positioned above a support layer 306. In some embodiments, the second surface of substrate layer 304 at least partially contacts a first surface of a support layer 306. In some embodiments, support layer 306 is positioned above or at least partially contacts a second substrate layer 308. In some embodiments, the second surface of support layer 306 at least partially contacts a first surface of second substrate layer 308. In some embodiments, at least one of support layer 306 and / or second substrate layer 308 comprise one or more windows, openings, pinholes, and / or pores which at least partially expose a surface (e.g., the top surface) of second barrier layer 304.

[0088] As seen in Figure 31, in some embodiments, an MIR detector 400 of the present invention comprises an MHP layer 402 positioned above or at least partially contacting a substrate layer 404. In some embodiments, substrate layer 404 is positioned above or at least partially contacting an enhancement layer 401. In some embodiments, a second or bottom surface of substrate layer 404 at least partially contacts a first or top surface of enhancement layer 401. In some embodiments, a second or bottom surface of MHP layer 402 at least partially contacts a first surface of a substrate layer 404. In some embodiments, substrate layer 404 is positioned above a support layer 406. In some embodiments, the second surface of substrate layer 404 at least partially contacts a first surface of a support layer 406. In some embodiments, support layer 406 is positioned above or at least partially contacts a second substrate layer 408. In some embodiments, the second surface of support layer 406 at least partially contacts a first surface of second substrate layer 408. In some embodiments, at least one of support layer 406 and / or second substrate layer 308 comprise one or more windows, openings, pinholes and / or pores which at least partially expose a surface (e.g., the top surface) of enhancement layer 401.

[0089] As seen in Figure 31, in some embodiments, an MIR detector 500 of the present invention comprises an MHP layer 502 positioned above or at least partially contacting barrier layer 503. In some embodiments, MHP layer 502 is positioned below or at least partially contacting an enhancement layer 501. In some embodiments, barrier layer 503 is positioned above or at least contacting substrate layer 504.

[0090] Substrate Layer

[0091] In some embodiments, devices of the present invention comprise, as a first layer, a low- thermal conductivity substrate layer. In some embodiments, the substrate layer has a low linear thermal conductivity. In some embodiments, the substrate layer has a linear thermal conductivity less than about 1 W m’IK’1. In some embodiments, the substrate layer has a linear thermal conductivity less than about 0.9 W m'1K'1, about 0.8 W m’1K'1, about 0.7 W m’1K'1, about 0.6 W m’1K’1, about 0.5 W m^ K’1, about 0.45 W m’1K’1, about 0.4 W m’1K’1, about 0.35 W m’ ^K'1, about 0.3 W m’^K’1, about 0.25 W m’1K’1, about 0.2 W m’1K’1, about 0.15 W m^ K'1, or about 0.1 W m ^K1.

[0092] In some embodiments, the substrate layer has a thickness less than about 1 mm. In some embodiments, the substrate layer has a thickness less than about 100 pm. In some embodiments, the substrate layer has a thickness less than about 10 pm. In some embodiments, the substrate layer has a thickness less than about 1 pm, also known as a thin floating-membrane structure.

[0093] In some embodiments, the substrate layer comprises paper and / or one or more polymers. In some embodiments, the substate layer comprises paper. In some embodiments, the substrate layer comprises silicon nitride. In some embodiments, the substrate layer comprises oxides, selected from oxide perovskites and lithium niobate. In some embodiments, the substrate layer comprises one or more polymers. In some embodiments, the one or more polymers are selected from the group consisting of nylon-6 (PA6), polyetheretherketone (PEEK), polytetrafluoroethylene (PTFE), poly (dimethyl siloxane) (PDMS), polysulfone (PSU), polymethylmethacrylate (PMMA), polycarbonate (PC), polyvinylchloride (PVC), polyvinylidene difluoride (PVDF), polyethylene terephthalate (PET), polystyrene (PS), polypropylene (PP), polyethylene (PE), and polyimide (PI). In some embodiments, the polymer is PET.

[0094] In some embodiments, the substrate layer comprises an inorganic membrane. Examples of inorganic membrane materials include, but are not limited to, aluminum oxide (AI2O3), silicon dioxide (SiCh), aluminum nitride (AIN), silicon nitrides (SixNy), and combinations thereof. In some embodiments, the substrate layer comprises silicon nitrides.

[0095] In some embodiments, the substrate layer has a thickness between about 500 nm and about 100 nm. In some embodiments, the substrate layer has a thickness of about 100 nm, about 120 nm, about 140 nm, about 160 nm, about 180 nm, about 200 nm, about 220 nm, about 230 nm, about 240 nm, about 245 nm, about 250 nm, about 255 nm, about 260 nm, about 265 nm, about 270 nm, about 275 nm, about 280 nm, about 290 nm, about 300 nm, about 320 nm, about 340 nm, about 360 nm, about 380 nm, about 400 nm, about 420 nm, about 440 nm, about 460 nm, about 480 nm, or about 500 nm.

[0096] In some embodiments, devices of the present invention comprise two substrate layers. In some embodiments, the two substrate layers sandwich a support layer. In some embodiments, the bottom substrate layer has one or more windows, openings, pores and / or etchings at least partially extending through the layer. In some embodiments, the one or more windows, openings, pores and / or etchings expose at least a portion of the support layer. In some embodiments, the support layer further has one or more windows, openings, pores and / or etchings at least partially extending through the layer that align with those in bottom substrate layer. In some embodiments, the one or more aligned windows, openings, pores and / or etchings in the bottom substrate layer and support layer expose at least a portion of the top substrate layer.

[0097] Metal Halide Perovskite Layer

[0098] In some embodiments, devices of the present invention comprise, as a second layer, a metal halide perovskite (MHP) layer. MHPs useful in the present invention include any known compound described in the art, for example see Li, et al. (Li, X., et al., 2021, Chem. Rev., 121(4):2230-2291)In some embodiments, the MHP layer comprises tin and / or lead. In some embodiments, the MHP comprises lead. In some embodiments, the MHP comprises germanium, silver, indium, and / or gold.

[0099] In some embodiments, the MHP layer comprises one or more halogens selected from the group consisting of bromine, iodine, and chlorine. In some embodiments, the halogen is iodine. In some embodiments, the halide of the perovskites can be replaced by chalcogenides, including sulfide and selenide.

[0100] In some embodiments, the MHP layer comprises one or more organic ammonium ligands. In some embodiments, the organic ammonium ligand is selected from the group consisting of a Ci-Cs alkylammonium ligand, a C2-C8 alkenylammonium ligand, a C2-C8 alkynylammonium ligand, a Ci-Cs substituted alkylammonium ligand, a C1-C12 heteroalkylammonium ligand, , a C3-C8 heterocyclylammonium ligand, a heteroarylammonium ligand, an optionally substituted aryl-(Ci-C6)alkylammonium ligand, an optionally substituted aryl-(C2-C6)alkenylammonium ligand, an optionally substituted aryl-(C2-C6)alkynylammonium ligand, an optionally substituted aryl-(Ci-C6)heteroalkylammonium ligand, and combinations thereof. In some embodiments, the organic ligand is selected from the group consisting of aromatic and thiophenic ligands.

[0101] In some embodiments, the organic ammonium ligand is a Ci-Cs alkylammonium ligand. In some embodiments, the Ci-Cs alkylammonium ligand is a primary alkylammonium ligand. In some embodiments, the Ci-Cs chain of the primary alkylammonium ligand is linear. In some embodiments, the Ci-Cs chain of the primary alkylammonium ligand is branched. In some embodiments, the Ci-Cs chain of the primary alkylammonium ligand is substituted.

[0102] In some embodiments, the Ci-Cs alkylammonium ligand is a C2-C8 secondary ammonium ligand. In some embodiments, one of the C1-C7 chains is linear. In some embodiments, both of the C1-C7 chains are linear. In some embodiments, one of the C1-C7 chains is branched. In some embodiments, both of the C1-C7 chains are branched. In some embodiments, one C1-C7 chain is linear and the other C1-C7 chain is branched. In some embodiments, one of the C1-C7 chains is substituted. In some embodiments, both C1-C7 chains are substituted.

[0103] In some embodiments, the Ci-Cs alkylammonium ligand is a C3-C8 tertiary ammonium ligand. In some embodiments, one of the Ci-Ce chains is linear. In some embodiments, two of the Ci-Ce chains are linear. In some embodiments, all three Ci-Ce chains are linear. In some embodiments, one of the Ci-Ce chains is branched. In some embodiments, two of the Ci-Ce chains are branched. Tn some embodiments, one of the Ci-Ce chains is substituted. In some embodiments, two of the Ci-Ce chains are substituted. In some embodiments, all three Ci-Ce chains are substituted.

[0104] In some embodiments, the organic ammonium ligand is an aryl-(Ci-C6)alkylammonium ligand. In some embodiments, the Ci-Ce chain is linear. In some embodiments, the Ci-Ce chain is branched. In some embodiments, the Ci-Ce chain is substituted. In some embodiments, the aryl group is substituted. In some embodiments, the Ci-Ce chain and aryl group are both substituted. In some embodiments, the aryl-(Ci-C6)alkylammonium ligand is 2 -phenyl- 1 -ethylammonium (phenyl ethyl ammonium).

[0105] In some embodiments, the organic ammonium ligands are accompanied by an anion. In some embodiments, the anion is an organic anion. In some embodiments, the anion is an inorganic anion. In some embodiments, the inorganic anion is a halide. In some embodiments, the halide is selected from bromide, iodide, and chloride. In some embodiments, chalcogenides replace the halide as the anions. In some embodiments, the halide of organic ammonium ligand is the same as the halide of the metal halide.

[0106] In some embodiments, the MHP layer comprises lead (II) iodide and an organic ammonium iodide ligand. In some embodiments, the MHP layer comprises lead (II) bromide and an organic ammonium bromide ligand. In some embodiments, the MHP layer comprises di(phenylethylammonium) lead (II) iodide ((PEA)2Pbl4). In some embodiments, the MHP layer comprises di (phenyl ethyl ammonium) lead (II) bromide ((PEA)2PbBr4).

[0107] In some embodiments, the MHP layer has a thickness less than about 10 pm, about 9 pm, about 8 pm, about 7 pm, about 6 pm, about 5 pm, about 4 pm, about 3 pm, about 2 pm, about 1.75 pm, about 1.5 pm, about 1.25 pm, about 1.2 pm, about 1.15 pm, about 1.1 pm, about 1.05 pm, or about 1 pm. In some embodiments, the MHP layer has a thickness less than about 1000 nm, about 950 nm, about 900 nm, about 850 nm, about 800 nm, about 750 nm, about 700 nm, or about 650 nm.

[0108] In some embodiments, the MHP layer has a thickness between about 1.5 pm and about 0.6 pm. In some embodiments, the MHP layer has a thickness between about 1 pm and about 0.6 pm. In some embodiments, the MHP layer has a thickness between about 950 nm and about 600 nm. In some embodiments, the MHP layer has a thickness between about 900 nm and about 600 nm. In some embodiments, the MHP layer has a thickness between about 850 nm and about 600 nm.

[0109] Barrier Layer

[0110] In some embodiments, devices of the present layer comprise a barrier layer. In some embodiments, the barrier layer comprises a composition which stabilizes the MHP layer. In some embodiments, the barrier layer comprises a composition which protects the MHP layer from conditions introduced in the addition of a fourth layer.

[0111] In some embodiments, the barrier layer comprises a transparent layer. In some embodiments, the barrier layer is transparent to visible light. In some embodiments, the barrier layer is transparent to IR light. In some embodiments, the barrier layer is transparent to MIR light. In some embodiments, the barrier layer is transparent to far-infrared light. In some embodiments, the barrier layer is transparent to terahertz light.

[0112] In some embodiments, the barrier layer comprises aluminum oxide (AI2O3), silicon dioxide (SiCh), aluminum nitride (AIN), or silicon nitrides (SixNy).

[0113] In some embodiments, the barrier layer has a thickness less than about 100 nm, about 90 nm, about 80 nm, about 70 nm, about 60 nm, about 50 nm, about 40 nm, about 30 nm, about 20 nm, about 19 nm, about 18 nm, about 17 nm, about 16 nm, about 15 nm, about 14 nm, about 13 nm, about 12 nm, about 11 nm, or about 10 nm.

[0114] In some embodiments, the barrier layer has a thickness between about 100 nm and about 10 nm. In some embodiments, the barrier layer has a thickness between about 76 nm and about

[0115] 15 nm. In some embodiments, the barrier layer has a thickness between about 76 nm and about

[0116] 22 nm. In some embodiments, the barrier layer has a thickness between about 76 nm and about

[0117] 29 nm. In some embodiments, the barrier layer has a thickness of about 15 nm, about 22 nm, about 29 nm, about 42 nm, or about 79 nm.

[0118] Enhancement Layer

[0119] In some embodiments, devices of the present invention comprise an enhancement layer. In some embodiments, the enhancement layer absorbs light of wavelengths not absorbed by the MHP layer. In some embodiments, the enhancement layer increases the ability of the device to absorb visible light. In some embodiments, the enhancement layer increases the ability of the device to absorb IR light. In some embodiments, the enhancement layer increases the ability of the device to absorb MIR light. In some embodiments, the enhancement layer increases the ability of the device to absorb far-IR light. In some embodiments, the enhancement layer increases the ability of the device to absorb terahertz light. In some embodiments, the enhancement layer increases the ability of the device to absorb sub-terahertz light (100 GHz to 1 THz).

[0120] In some embodiments, the enhancement layer comprises light-absorbing nanocrystals. In some embodiments, the nanocrystals comprise one or more metal oxides. In some embodiments, the nanocrystals comprise one or more selected from the group consisting of cadmium oxide (CdO), indium-cadmium oxides (In-CdO; “ICOs”), fluorine-indium-cadmium oxides (F-Id-CdO; “FICOs”) tin oxide (SnCh), antimony-tin oxides (Sb-SnCh; “ATO”), indium-tin oxides (In-SnCh; “ITOs”), aluminum-zinc oxide (AZO), tungsten-tin oxides (W-SnO2; “TTOs”), cesium-tungsten- tin oxides (Cs-W-SnO?; CWTOs”), tungsten oxides (WO2 and / or WO3), and cesium-tungsten oxides (CS-WO2 / WO3; “CWOs”). In some embodiments, the enhancement layer comprises lightabsorbing plasmonic structures made of elementary metals, including, but not limited to, gold, silver, and aluminum.

[0121] In some embodiments, the enhancement layer has a thickness of less than about 1000 nm, about 950 nm, about 900 nm, about 850 nm, about 800 nm, about 750 nm, about 700 nm, about 650 nm, about 600 nm, about 550 nm, about 500 nm, about 450 nm, about 400 nm, about 350 nm, about 300 nm, about 275 nm, about 250 nm, about 225 nm, about 200 nm, about 175 nm, or about 150 nm.

[0122] In some embodiments, the enhancement layer has a thickness of at least about 50 nm, about 75 nm, about 100 nm, about 125 nm, about 150 nm, about 175 nm, about 200 nm, about 225 nm, or about 250 nm.

[0123] In some embodiments, the enhancement layer has a thickness of between about 50 nm and about 300 nm. In some embodiments, the enhancement layer has a thickness of between about 75 nm and about 250 nm. In some embodiments, the enhancement layer has a thickness of between about 100 nm and about 200 nm. In some embodiments, the enhancement layer has a thickness of between about 125 nm and about 175 nm. In some embodiments, the enhancement layer has a thickness of about 150 nm. Support Layer

[0124] In some embodiments, devices of the present invention comprise a support layer. In some embodiments, the support layer provides structural support for a substrate layer.

[0125] In some embodiments, the support layer comprises one or more windows, openings, pores and / or etchings at least partially extending through the layer. In some embodiments, the one or more windows, openings, pores, and / or etchings expose at least part of the surface of a substrate layer.

[0126] In some embodiments, the substrate layer comprises a semiconductive material. Examples of semiconductive materials include, but are not limited to, carbon, silicon, germanium, tin, selenium, tellurium, gallium arsenide, silicon carbide, sulfur, boron nitride, boron phosphide, boron arsenide, aluminum nitride, aluminum phosphide, aluminum arsenide, and any other semiconductive material known in the art (e.g., those disclosed in Kasap, S., et al., “Springer Handbook of Electronic and Photonic Materials,” Springer, 2006). In some embodiments, the semiconductive material is silicon.

[0127] Method of Production

[0128] Referring now to Figure 16, shown are exemplary methods of fabrication or production for MIR detectors according to aspects of the present invention. In some embodiments, exemplary methods comprise fabricating or producing a detector, a photodetector, or a stack. In some embodiments, devices of the present invention are formed from an Enhancement / MHP / Substrate arrangement or stack, in which the enhancement layer is on a surface of the MHP layer opposite the surface of the MHP layer contacting the substrate layer. In some embodiments, devices of the present invention are in an MHP / Substrate / Enhancer arrangement, in which the enhancement layer is on a surface of the substrate layer opposite the surface of the substrate layer contacting the MHP layer. In some embodiments, the methods comprise creating a pinhole in a bottom substrate layer (e.g., an SiNx pinhole), followed by silicone etching of the support layer. In some embodiments, the methods comprise PEA spincoating onto the substrate layer to form an MHP layer. In some embodiments, the methods comprise ICO spin coating onto the MHC layer to form an enhancement layer. In some embodiments, the methods comprise ICO spin coating onto an exposed surface of the substrate layer opposite the MHP layer. In some embodiments, the present invention provides methods of producing an MIR detection device of the present invention. In some embodiments, the method of producing an MIR device comprises: a) obtaining a substrate layer; b) obtaining a solution comprising a metal halide of interest and an organic ammonium halide of interest; c) coating the substrate with the solution; and d) annealing the coating onto the substrate to form a MHP layer.

[0129] In some embodiments, step a) further comprises treating the substrate layer to improve the evenness or maximize the coverage by the solution. In some embodiments, the method of treating the substrate layer is selected from the group corona treatment, UV / ozone treatment, plasma treatment, and flame treatment. In some embodiments, the method of obtaining the support layer involves chemical etching off silicon, starting from a silicon nitride on silicon wafer; this process yields a thin floating silicon nitride membrane with thicknesses between several micrometers down to tens of nanometers.

[0130] In some embodiments, step d) is accomplished by a method selected from the group consisting of spin coating, spray coating, dip coating, flow coating, brush coating, inkjet printing, physical vapor deposition, and combinations thereof.

[0131] In some embodiments, the method further comprises: e) coating the exposed MHP layer with a protection layer of AI2O3.

[0132] In some embodiments, the method comprises: f) coating the exposed MHP layer or exposed AI2O3 layer with a layer of MIR-absorbing nanocrystals.

[0133] In some embodiments, the method comprises steps a) through d). In some embodiments, the method comprises steps a) through e). In some embodiments, the method comprises steps a) through d) and step f). In some embodiments, the method comprises steps a) through step f).

[0134] In some embodiments, step e) is accomplished by evaporative deposition, chemical vapor deposition, sputtering, pulsed-laser deposition, or atomic layer deposition. In some embodiments, step f) is accomplished by a method selected from the group consisting of spin coating, spray coating, dip coating, flow coating, brush coating, inkjet printing, physical vapor deposition, and combinations thereof.

[0135] EMBODIMENTS

[0136] Embodiment l is a thin-layer device for detection of mid-infrared light (MIR) comprising a layer of a metal halide perovskite (MHP) film on a layer of a low-thermal conductivity polymer or a thin inorganic membrane.

[0137] Embodiment 2 is the device of embodiment 1, wherein the MHP comprises a lead halide and an ammonium salt.

[0138] Embodiment 3 is the device of embodiment 1 or 2, wherein the lead halide is selected from PbCk, PbBn, and Pbh.

[0139] Embodiment 4 is the device of any one of embodiments 1-4, wherein the ammonium salt is selected from the group consisting of MeNHsCl, MeNHsBr, MeNH3I, EtNHsCl, EtNHsBr, EtNH3I, n-PrNH3Cl, n-PrNH3Br, n-PrNH3I, i-PrNH3Cl, i-PrNH3Br, i-PrNH3I, n-BuNHsCl, n- BuNH3Br, n-BuNH3I, i-BuNH3Cl, i-BuNH3Br, i-BuNHsI, s-BuNH3Cl, s-BuNH3Br, s-BuNH3I, t- BuNH3Cl, t-BuNH3Br, t-BuNH3I, PhCH2NH3Cl, PhCH2NH3Br, PhCH2NH3I, PhCH2CH2NH3Cl, PhCH2CH2NH3Br, PhCH2CH2NH3I, PhCH2CH2CH2NH3Cl, PhCH2CH2CH2NH3Br, and PhCH2CH2CH2NH3I.

[0140] Embodiment 5 is the device of any one of embodiments 1-4, wherein the MHP is (PhCH2CH2NH3)2Pbl4.

[0141] Embodiment 6 is the device of any one of embodiments 1-5, wherein the low-thermal conductivity polymer has a thermal conductivity less than about 0.25 W m’1K'1.

[0142] Embodiment 7 is the device of any one of embodiments 1-6, wherein the low-thermal conductivity polymer is one or more selected from the group consisting of nylon-6 (PA6), polyetheretherketone (PEEK), polytetrafluoroethylene (PTFE), poly(dimethylsiloxane) (PDMS), polysulfone (PSU), polymethylmethacrylate (PMMA), polycarbonate (PC), polyvinylchloride (PVC), polyvinylidene difluoride (PVDF), polyethylene terephthalate (PET), polystyrene (PS), polypropylene (PP), polyethylene (PE), and polyimide (PI). Embodiment 8 is the device of any one of embodiments 1-7, wherein the low-thermal conductivity polymer is PET.

[0143] Embodiment 9 is the device of any one of embodiments 1-8, wherein the MHP is (PhCH2CH2NH3)2Pbl4.

[0144] Embodiment 10 is the device of any one of embodiments 1-9, wherein the thickness of the MHP layer is between about 100 nm and about 10,000 nm.

[0145] Embodiment 11 is the device of any one of embodiments 1-10, wherein the thickness of the MHP layer is between about 500 nm and about 1,000 nm.

[0146] Embodiment 12 is the device of any one of embodiments 1-11, wherein the thickness of the MHP layer is about 940 nm.

[0147] Embodiment 13 is the device of any one of embodiments 1-12, wherein the device further comprises a layer of infrared-absorbing nanocrystals on the MHP face opposite the PET.

[0148] Embodiment 14 is the device of any one of embodiments 1-13, wherein the infraredabsorbing nanocrystals comprise cadmium oxide (CdO).

[0149] Embodiment 15 is the device of any one of embodiments 1-14, wherein the infraredabsorbing nanocrystals further comprises one or more dopants selected from the group consisting of indium, fluorine, gold, silver, and aluminum.

[0150] Embodiment 16 is the device of any one of embodiments 1-15, wherein the thickness of the layer of infrared-absorbing nanocrystals is between about 100 nm and about 300 nm.

[0151] Embodiment 17 is the device of any one of embodiments 1-16, wherein the thickness of the layer of infrared-absorbing nanocrystals is about 150 nm.

[0152] Embodiment 18 is the device of any one of embodiments 13-17, wherein the device further comprises a layer of aluminum oxide (Al2Ch) between the MHP and the infraredabsorbing nanocrystals.

[0153] Embodiment 19 is the device of any one of embodiments 1-5, wherein the thin inorganic membrane comprises one or more selected from the group consisting of aluminum oxide, silicon oxide, aluminum nitride, and silicon nitride.

[0154] Embodiment 20 is the device of embodiment 1 or 19, wherein the inorganic membrane comprises silicon nitride. Embodiment 21 is the device of any one of embodiments 1, 19, and 20, wherein the device further comprises a substrate layer on the thin inorganic membrane face opposite the MHP layer.

[0155] Embodiment 22 is the device of embodiment 21, wherein the substrate layer comprises silicon.

[0156] Embodiment 23 is the device of embodiment 21 or 22, wherein the substrate layer comprises a opening exposing the surface of the thin inorganic membrane.

[0157] Embodiment 24 is the device of any one of embodiments 1 and 19-23, wherein the MHP is (PhCH2CH2NH3)2Pbl4.

[0158] Embodiment 25 is the device of any one of embodiments 1 and 19-24, wherein the thickness of the MHP layer is between about 100 nm and about 10,000 nm.

[0159] Embodiment 26 is the device of any one of embodiments 1 and 19-25, wherein the thickness of the MHP layer is between about 500 nm and about 1,000 nm.

[0160] Embodiment 27 is the device of any one of embodiments 1 and 19-26, wherein the thickness of the MHP layer is about 940 nm.

[0161] Embodiment 28 is the device of any one of embodiments 1 and 19-27, wherein the device further comprises a layer of infrared-absorbing nanocrystals.

[0162] Embodiment 29 is the device of embodiment 28, wherein the infrared-absorbing nanocrystals comprise cadmium oxide (CdO).

[0163] Embodiment 30 is the device of embodiment 28 or 29, wherein the infrared-absorbing nanocrystals further comprises one or more dopants selected from the group consisting of indium, fluorine, gold, silver, and aluminum.

[0164] Embodiment 31 is the device of any one of embodiments 28-30, wherein the thickness of the layer of infrared-absorbing nanocrystals is between about 100 nm and about 300 nm.

[0165] Embodiment 32 is the device of any one of embodiments 28-31, wherein the thickness of the layer of infrared-absorbing nanocrystals is about 150 nm.

[0166] Embodiment 33 is the device of any one of embodiments 28-32, wherein the layer of infrared-absorbing nanocrystals is on the MHP face opposite the thin inorganic membrane.

[0167] Embodiment 34 is the device of any one of embodiments 28-32, wherein the layer of infrared-absorbing nanocrystals is on the exposed surface of the thin inorganic membrane. Embodiment 35 is the device of any one of embodiments 1 and 19-34, wherein the device further comprises a second layer of thin inorganic membrane on the support layer face opposite the first layer of thin inorganic membrane.

[0168] EXPERIMENTAL EXAMPLES

[0169] The invention is further described in detail by reference to the following experimental examples. These examples are provided for purposes of illustration only, and are not intended to be limiting unless otherwise specified. Thus, the invention should in no way be construed as being limited to the following examples, but rather, should be construed to encompass any and all variations which become evident as a result of the teaching provided herein.

[0170] Without further description, it is believed that one of ordinary skill in the art can, using the preceding description and the following illustrative examples, make and utilize the compounds of the present invention and practice the claimed methods. The following working examples therefore, specifically point out the preferred embodiments of the present invention, and are not to be construed as limiting in any way the remainder of the disclosure.

[0171] Example 1: Development of a Multi-Layer Detector of Mid-Infrared Light

[0172] Metal halide perovskites (MHPs) have emerged as solution-processable semiconductors with attractive applications in photovoltaics and optoelectronics (Kojima, A., et al., 2009, Journal of the American Chemical Society, 131 :6050-6051; Bai, S., et al., 2019, Nature, 571 :245-250; Wei, H., et al., 2016, Nature Photonics, 10:333-339; Sutherland, B. R. and Sargent, E. H., 2016, Nature Photonics, 295-302; Tan, S., et al., 2022, Nature, 605:268-273; Xiao, Z., et al., 2017, Nature Photonics, 11 : 108-115). The strong electron-phonon interactions in MHPs yield temperature-dependent linewidths of photoluminescence and facilitate the formation of polarons, which dominate trapping, transport, and recombination of charge carriers in these materials (Wright, A. D., et al., 2016, Nature Communications, 7:11755; Guo, Y., et al., 2019, Nature Communications, 10: 1175; Miyata, K., et al., 2017, Scientific Advances, 3:el701217; Guzelturk, B., et al., 2021, Nature Materials, 20:618-623). Two-dimensional (2D) MHPs represent a structurally and chemically diverse sub-class of the MHP family (Saparaov, B. and Mitzi, D. B., 2016, Chemical Reviews, 116:4558-4596; Li, X., et al., 2021, Chemical Reviews, 121 :2230- 2291; Tsai, H., et al., 2016, Nature, 536:312-316). The charge-insulating organic-spacer cations in 2D-MHPs not only impose dielectric and quantum confinements on the charge carriers, leading to formation of excitons with spectrally narrow and strong optical absorption at room temperature, but also strongly impede heat flow along the cross-plane direction (Katan, C., et al., 2019, Chemical Reviews, 119:3140-3192; Straus, D. B. and Kagan, C. R., 2018, Journal of Physical Chemistry Letters, 9: 1434-1447; Blancon, J.-C., et al., 2020, Nature Nanotechnology, 15:969-985; Guo, P., et al., 2018, Natuer Communications, 9:2019; Giri, A., et al., 2020, Nano Letters, 20:3331-3337; Li, C., et al., 2021, Nano Letters, 21 :3708-3714).

[0173] Perovskite Thin Films as a Detector of Mid-Infrared Light

[0174] Di(phenylethylammonium) lead (II) iodide ((PEA)2Pbl4, hereinafter “PEA”) shows a temperature-dependent reflectance spectra as single crystals (Figure 1A). The spectra were measured with randomly polarized light at normal incidence on the crystalline a-b plane, which is defined to be parallel to the octahedral layers. The exciton resonance is manifested as a peak in reflectivity near 520 nm and a dip on the shorter- wavelength side. Such a spectral feature in reflectance can be quantitatively captured by modeling the exciton resonance using a Lorentzian oscillator (Equation 1), with which the relative permittivity at angular frequency co (Li, S., et al., 2022, Physical Review Letters, 129: 177401; Li, Y., et al., 2014, Physical Review B, 90:205422; Scuri, G., et al., 2019, Physical Review Letters, 120:037402). icoy

[0175] (Equation 1)

[0176] By fitting the reflectance spectrum at room temperature, we obtained the high-frequency permittivity = 5.07, oscillator strength AL= 1.15 eV, exciton energy coL= 2.39 eV, and damping factor y = 67 meV (Figure 2).

[0177] As shown in Figure 1A, the resonant feature in reflectance strengthens with decreasing temperature, which results in a further increase (decrease) of reflectivity at the reflectance peak (dip) (Guo, P., et al., 2018, Physical Review Letters, 121: 127401; Yaffe, O., et al., 2015, Physical Review B, 92:045414). This trend arises from reduced electron-phonon interactions at lower temperatures, leading to homogeneous exciton line-narrowing. The low reflectivity value at the reflectance dip (500-510 nm) and its spectral shift with temperature yield a large temperature coefficient of reflectivity (TCR), defined as the relative change in reflectivity per degree change in temperature (Equation 2; T = temperature; R = temperature-dependent reflectivity).

[0178] R(T + dT) - R(T)

[0179] TCR(T) =

[0180] R(T) ■ dT

[0181] (Equation 2)

[0182] As shown in Figure IB, at ambient temperature the TCR is 0.52%-K'1, which goes up to 2% K-1at liquid-nitrogen temperature. The wavelength of maximal TCR slightly varies with temperature due to the spectral shift of the reflectance dip (Figure 3). Similar to other n = 1 2D- MHPs, spin-coated PEA films exhibit a high degree of out-of-plane alignment (i.e., a-b planes parallel to substrates), as verified with X-ray diffraction (XRD; Figure 4) (Tsai, H., 2016, Nature, 536:312-316). Figure 1C shows the temperature-dependent reflectance spectra for a 1.0 pm-thick spin-coated PEA film. Since the thickness is larger than the optical penetration depth around the exciton resonance (Figure 2D), the film is considered ‘infinitely’ thick, and the reflectance is substrate-blind. The film exhibits a TCR of approximately 0.3%-K'1at ambient temperature (Figure IB). The lower TCR of the film compared to its single-crystal counterpart likely arises from disordered in-plane crystallographic orientations, strain imposed by the substrate, and defects, which yield additional exciton damping pathways as evident from the broadened resonance in the reflectance spectra (Figure 1C).

[0183] The sizeable exciton-enabled TCR of PEA single crystals and films offers an opportunity for all-optical MIR photodetection, where the MIR light-induced temperature rise of PEA is detected by measuring the relative change in reflectivity at the reflectance dip where the TCR is maximized. In general, light-induced temperature effects are strong in materials with low K. Due to the high density of organic-inorganic interfaces, and the weak van der Waals forces connecting the organic cations between neighboring layers, 2D-MHPs have some of the lowest K among extended solids especially along the cross-plane direction (Guo, P., et al., 2019, Nature Communications, 9:2019).

[0184] Infrared-pump visible-probe (IP VP) transient reflection experiments for a 640 nm-thick PEA film deposited on crystalline Si to determine the cross-plane K of PEA at ambient temperature. The PEA was vibrationally (i.e., thermally) excited by MIR pulses centered at 3170 nm (resonant with the N-H and C-H stretching modes) and the pump-induced reflectance change was captured by a time-delayed, broadband visible probe (Li, S., et al., 2022, Review of Scientific Instruments, 93:053003). Since the pump photon energy is much lower than the electronic bandgap, the relevant process is pump-induced, impulsive lattice heating, followed by its subsequent dissipation. The measured AR / R transient spectral map is shown in Figure 5, where the differential change in reflectivity is calculated according to Equation 3, with R(0) being reflectivity prior to pump excitation and R(t) being reflectivity at delay time t after pump excitation. (Equation 3)

[0185] The AR / R spectra exhibit a derivative-like line-shape, transitioning from positive to negative at a zero-crossing wavelength of approximately 507 nm. The AR / R spectra, when compared with the steady-state data (Figures 1A and 1C), indicate impulsive pump-induced lattice heating followed by slow cooling in the ps timescale. Since lattice cooling typically takes nanoseconds (e.g., as measured in time-domain thermoreflectance), the ps cooling time here reveals an ultralow cross-plane K of PEA along the cross-plane direction (Jiang, P., 2018, Journal of Applied Physics, 124: 161103).

[0186] Exemplary applications utilizing the perovskite thin films as described herein include thermal metrology, night vision applications, gas and molecular sensing, bio-imaging, environmental monitoring, free-space communication, thermal energy harvesting, and any other suitable imaging or sensing application utilizing the mid-infrared (MIR) wavelength range which includes both mid-wave infrared (MWIR, 3~5 pm) and long-wave infrared (LWTR, 8—14 pm) wavelengths. Furthermore, a device may utilize the perovskite thin films as described herein in resonant optical structures to extend to additional light wavelength ranges. In some example embodiments, the perovskite thin films may be deployed across a trench style device to form a floating structure above a gap comprising an air-gap, fluid-gap, or vacuum-gap, to further enhance heat sensitivity by orders of magnitude.

[0187] Polyethylene Terephthalate Enhances Heat Retention

[0188] Using the finite-element method, the heat transfer process in PEA / Si was simulated, with PEA subject to impulsive thermal excitation. The initial temperature profile in PEA was determined by its absorption coefficient at the MIR pump wavelength. A linear relationship was assumed between the measured AR / R and the simulated temperature rise (denoted as AT, averaged over the probe penetration depth). By sweeping the K of PEA and the interfacial thermal conductance (G) between PEA and Si, the time-dependent AT was calculated, and with it the time-integrated differences between the decays of AR / R and AT. The obtained difference map (Figure ID) distills K = 0.20 W ■ m-1■ K-1for PEA (assuming G > 20 MW ■ m-2■ K-1). The sensitivity analysis in Figure IE indicates that the estimated K of PEA should lie within ±20% from the true value.

[0189] Having determined the K, the figure of merit, defined as TCR / (K CP), can be calculated to quantify material performance for bolometer applications, as a higher TCR, lower K, and lower CPall contributed to improved MIR light-induced material response. As presented in Table 1, PEA exhibits a figure-of-merit an order of magnitude higher than current state of the art bolometer material VOXin the MIR light-induced response (Kizuka, H., et al., 2015, Japanese Journal of Applied Physics, 54:053201; Oh, D.-W., et al., 2010, Applied Physics Letters, 96: 151906). The sizeable TCR and exceptional heat retention of 2D-MHPs motivated us to repurpose these materials for MIR photodetection.

[0190] Table 1. A comparison between the state-of-the-art bolometer material VOx and PEA.

[0191] The figure of merit is defined as TCR / (K ■ Cp) with a dimension of 10'6kg m s K2. R denotes resistivity for VOx and reflectivity for PEA. All properties are for room temperature.

[0192] Interfacing PEA with MIR-ab sorbing nanoantennas

[0193] To enable photodetection, plastic polyethylene terephthalate (PET) was employed as the underlying substrate to enhance heat retention with the PEA film, leveraging the low K of PET (< 0.20 W ■ m-1■ K-1). The transient AR / R spectral map from IPVP experiments for a 940 nm- thick PEA film spin-coated on a PET substrate is shown in Figure IF. Importantly, the slow decay of AR / R takes tens of ps (i.e., an order of magnitude longer than PEA / Si), suggesting effective heat retention within the PEA film. However, similar to VOx, 2D-MHPs are transparent to MIR light except at discrete vibrational frequencies of the organic spacers. Strong MIR light absorbers need to be placed in proximity to 2D-MHPs, preferably away from the substrate. To this end, localized surface plasmon resonances (LSPRs) provide a strong optical absorption cross-section with sub -wavelength material volumes. Accordingly, LSPRs of indium-doped cadmium oxide (ICO), a type of transparent conducting oxide (TCO) with low optical loss and tunable electron concentration, were utilized (Boltasseva, A. and Atwater, H. A., 2011, Science, 331 :290-291; Guo, P., et al., 2016, Nature Photonics, 10:267-273; Agrawal, A., et al., 2018, Chemical Reviews, 118:3121-3207). Besides providing MIR absorption, another important advantage of TCOs is visible transparency, making them compatible with the all-optical detection scheme here.

[0194] Colloidal nanocrystals (NCs) of ICO were synthesized with high size uniformity by established ramped heating methods (Gordon, T. R., et al., 2013, Nano Letters, 13:2857-2863). By adjusting the dopant concentrations, three different NCs were prepared, and with a decreasing doping concentration, the NCs dissolved in carbon tetrachloride exhibit LSPRs centered at 1.6, 2.4, and 3.4 pm (Figure 6). Due to increased inter-particle interactions and higher dielectric constants of the surrounding medium, spin-casted NC fdms show redshifted LSPRs centered at 2.0, 3.0, and 4.4 pm (Figure 7A); The NCs are denoted as FICO (fluorine- and indium-doped cadmium oxide), ICO-1 (indium-doped cadmium oxide-1), and ICO-2, respectively.

[0195] NC films were spin-coated onto PEA / PET stacks. A 15-nm, visibly transparent AI2O3 layer was pre-evaporated on the PEA / PET to prevent PEA from being damaged by toluene (the solvent for the ICO NCs). Figure 7B shows a cross-sectional scanning electron micrograph of the ICO-l / PEA / PET stack; the corresponding XRD pattern illustrates the structural integrity of the PEA film with NC deposition. MIR transmittance spectra of the three types of ICO / PEA / PET samples are plotted in Figure 7C. Notably, the absorption of MIR light by ICO NCs is largely preserved for the stacks, indicating effectiveness of the LSPR-enabled, spectrally tunable MIR absorption. Note that the LSPR absorption of ICO-1 overlaps with, but is much broader than, the N-H stretching absorption of PEA. The transient AR / R spectral map (Figure 7D) for the ICO- l / PEA / PET sample, pumped at 3170 nm, displays a similarly slow timescale as the PEA / PET (Figure IF). However, the AR / R of ICO-l / PEA / PET undergoes a slower rise (-100 ns) after time zero, whereas the AR / R of PEA / PET rises instantaneous following pump excitation (Figure 7E and Figure 8). Such disparity is also observed for samples on Si substrates (Figure 9). Due to the visible transparency of ICO, the AR / R at 500 nm primarily arises from the temperature increase of PEA, hence the 100 ns rise of AR / R can be ascribed to the NC-to-PEA heat transfer (Figure 10). Given a lack of knowledge on the K for the NC film, several different K were utilized for the NC film to simulate heat transfer from NC to PEA using the finite-element method and plotted the AT for PEA (averaged over the probe penetration depth). The range of K (0.2-0.5 W m’1K’1) in these simulations is informed by thermal-transport studies on semiconductor NC films, which found similar K values for a wide range of NC solids (Ong, W.-L., et al., 2013, Nature Materials, 12:410-415). For PEA, AT is largely independent of the K of the NC film (Figure 7F), and the simulated temporal profiles of temperature rise match well with the measured kinetics of AR / R. Inspection of the AR / R spectrum (Figure 7G) shows that the maximal TCR at room temperature is centered at approximately 500 nm. A bi -exponential fit to the 500-nm AR / R kinetics distills exponential time constants of 1.2 ps and 9.2 ps in the 35-ps time window (Figure 7H).

[0196] Spectrally tunable MIR detection with PET-supported PEA

[0197] With understanding of the optical and thermal-transport properties of 1CO / PEA / PET stacks, all-optical MIR photodetection experiments were designed and executed, as depicted in Figure 11 A. A bandpass filter of 500 ± 5 nm defined a monochromatic probe at a wavelength where the sample exhibits highest sensitivity to temperature. A broadband quasi-continuous- wave laser served as the MIR source, and five different MIR bandpass filters (Figure 12) were used to select the wavelengths of MIR light incident on the sample. The MIR light was modulated by a mechanical chopper to enable lock-in detection of the variation in the reflected probe intensity.

[0198] Figure 1 IB summarizes the all-optical MIR detection results for PEA / PET coated with the three different ICO NCs measured at ambient temperature. Consistent with LSPR-enabled absorption (Figure 7C and Figure 13), the sensitivities of the samples all peak at the LSPR maxima wavelengths of the corresponding NC films. On top of this, all the samples show photoresponses at 3—3.5 pm, which arises from N-H stretching absorption of PEA. As summarized in Figure 14, the measured lock-in voltage is linearly proportional to the incident MIR power the samples at all wavelengths, indicating a linear operational regime. Films on PET substrates show a sensitivity an order-of-magnitude higher than those on Si (Figure 1 IB), which is in line with enhanced thermal retention with PET substrates (Figure 5 vs. Figure 7D). The mV-level lock-in voltage is a few thousandths of the PMT total output voltage (~0.5 V), from which a relative change in reflectance was estimated to be less than one percent and hence a temperature modulation on the order of 1 K.

[0199] By varying the chopping frequency, the lock-in voltage was found to increase with a decreasing chopping frequency over the explored range of 5000 Hz to 100 Hz (Figure 11C). Such monotonic relationship implies a long thermal time constant of at least 10 ms for the ICO / PEA / PET stacks. Thermal-transport simulations with impulsive heating at time zero (Figure 15) reveal that although the AT of PEA undergoes substantial decay by 100 ps (i.e., in accordance with the IP VP results in Figure 7H), the AT has a very long-lived tail. The thermal accumulation effect stemming from the long-lived component underpins the higher lock-in voltage achieved at lower chopping rates, and these results indicate that higher sensitivity can be achieved by further reducing the chopping rate at a cost of the detection bandwidth. To test the lowest MIR detection limit, an ICO-l / PEA / PET sample was examined under variable MIR powers at a wavelength of 3.33 pm with 100 Hz of MIR modulation frequency. As shown in Figure 1 IE, the smallest detectable power density, defined as when the signal is equivalent to the noise, reaches below 1 nW- pm'2. The ratio of the smallest detectable lock-in voltage (0.07 mV) and the PMT voltage (0.5 V) corresponds to a AR / R of -0.014%.

[0200] Sensitivity Enhancement by Membrane-Based Structures

[0201] To further enhance the sensitivity to levels below the nW- pm2range, a unique membrane-based structure was developed, leveraging the anisotropic wet chemical etching properties of silicon. The rationale behind this design is that a membrane-based architecture can suppress vertical heat flow channels and make in-plane heat flow less efficient. Figure 15A shows a schematic of the obtained PEA / SiNVICO structure. As illustrated in Figure 16, the process begins with a commercially obtained low-stress Si N. -coated Si wafer, with a SiNx thickness of 265 nm. Utilizing the well-established KOH wet-chemical etching method, tens-to- hundred pm-sized SiNx membrane windows were created on Si substrates. A film of PEA was then spin-coated onto the SiNx membrane, followed by the application of an ICO NC film, which was spin-coated onto the reverse side of the SiNx membrane. The heat dissipation rates of the membrane structures were then evaluated through TR experiments. As shown in Figure 15B, the decay of R / R occurs over a duration exceeding one millisecond. This level of heat retention, much more effective than that of PET substrate-supported stacks (Figure 7B and Figure 7H), contributes to a significant improvement in MIR detectivity. As illustrated in Figure 15C, an order of magnitude enhancement in detectivity was achieved, reaching the tens of pW pm'2range, all while maintaining a fixed MIR modulation frequency of 80 Hz.\

[0202] Additionally, the sensitivity is improved by exploiting the nontrivial phase shift that occurs at the interface between the optically lossy PEA, especially near its exciton resonance, and a lossless dielectric material. As demonstrated in Figure 17A, a thin dielectric coating onto the PEA enables enhanced absorption in PEA even with dielectric layers being considerably thinner than a quarter- wavelength (A / 4) (Kats, M. A., et al., 2013, Nature Materials, 12(l):20- 24). For illustrating this concept, the transfer-matrix approach was used to calculate the reflectance spectra of PEA covered by a dielectric layer of varying thickness, using SiN.v as a model dielectric material. The calculated reflectance map in Figure 17B shows that the interference effects caused by the phase shift at the PEA / SiN.v interface drastically alter the reflectance characteristics near the exciton resonance of PEA. The data further reveals that the changes in reflectance near the exciton resonance are periodic in the coating thickness and, crucially, for certain SiN-,- coating thicknesses, specifically around 30, 150 and 270 nm, the reflectance can approach nearly zero, corresponding to complete optical absorption by the PEA.

[0203] Importantly, a low steady-state reflectance (A) is advantageous for this MIR detection scheme. This is because, by comparing the R / R map in Figure 17C and the reflectance in Figure 17B, a lower reflectance R leads to an increased relative change in reflectance (Al? / R, where steady-state reflectance R is the denominator). The AR / R is a critical factor in signal readout for a fixed increase in exciton damping (Ay) or, equivalently, a fixed temperature rise in the PEA layer. Theoretically, as the steady-state reflectance approaches zero, the value of A / ? / / ? tends to diverge. However, in practice, limitations to this divergence in enhancement exist, including those arising from the interfacial roughness between PEA and SiNx, non-uniformity of the PEA film, and the thickness variation of the SiN.-..-, placing a ceiling on the maximum achievable MIR sensitivity. Despite these practical constraints, this dielectric-coating strategy still holds significant promise to further improve the sensitivity of the platform beyond the tens of pW pirT2range. While the dielectric layer depicted in Figure 17A can be deposited onto PEA using straightforward physical vapor deposition techniques, we found an intriguing alternative by treating the PEA-supporting SiNx membrane itself as the dielectric layer. Notably, this approach is viable when the probe is incident on the SiN.v side rather than directly on the PEA. To accommodate this, the device structure used in Figure 15 was slightly modified. The new structure, ICO / PEA / SiN.-,, and the associated configuration for MIR detection, is depicted in Figure 17D (see Figure 16 for sample fabrication details). The SiNx thickness was chosen to be 265 nm since it is close to the condition where R / R reaches a high value (Figure 17C). The measurements on ICO / PEA / SiNx utilize a counter-propagating configuration, where the MIR light and visible probe light shine on the sample from opposing directions. Consistent with the transfer-matrix calculations, measurements, as summarized in Figure 17E, showed that when covered with the 265-nm thick SiNx, the PEA displays a lower reflectance at its resonance dip and, importantly, a higher quality factor (i.e., sharper reflectance dip), when compared to an uncovered PEA film, all measured at room temperature. The MIR sensitivity, manifested as the measured lock-in voltage in Figure 17E, reaches a maximum when using a probe wavelength matching the reflectance dip. The MIR sensitivity of the dielectric layer-enhanced device was tested by using ICO-1 as the MIR absorber. MIR power-dependent measurements (Figure 17F), utilizing a probe with 8 nm full-width-half-maximum (FWHM) in spectral bandwidth and a MIR pump centered at 3.33 pm, indicate that the structure achieves a remarkable sensitivity below 10 pW pm'2, nearly two orders of magnitude more sensitive than a previous report utilizing ratiometric luminescence (Liang, L., et al., 2022, Nature Photonics, 16(10):712-717).

[0204] To demonstrate the versatility of the approach, the detection from the MWIR range of 2-4.5 pm was expanded to the LWIR range at 10.6 pm, utilizing a CO2 laser as the MIR excitation source. Here, a simpler SiNx / PEA bilayer structure was employed, excluding the ICO NC layer. As shown in Figure 18A, the infrared-active Si-N stretching mode of the SiNx fdm leads to a broad and efficient vibrational absorption centered between 10 and 13 pm, achieving -50% absorption at 10.6 pm (Liu, F., et al., 2004, Journal of Applied Physics, 96(5):2973-2979). A MIR sensitivity of 15.6 pW- pm'2at this wavelength was achieved (Figure 18B), which is comparable to the performance observed in the MWIR regime. The sensitivity of our scheme can be further improved by optimizing the SiNx layer thickness (i.e., matching the conditions that produce maximum enhancement of R / R in Figure 17C), increasing the interfacial contact between SiN> and PEA (potentially by adopting single-crystalline membranes), and simultaneously employing a probe light of a narrower spectral bandwidth with full-width-at-half- maximum of 1~2 nm. The last point is further illustrated in Figure 18C, where stronger R / R occurs at discrete, precise thicknesses of SiN when measured with a spectrally narrow probe. Cryogenic operation can also enable larger sensitivity due to a higher TCR of PEA at lower temperatures (Figure IB, Figure 19, and Figure 20).

[0205] Imaging By MIR Photodetection

[0206] The all-optical MIR detection scheme can was extended to an imaging modality by harvesting mature Si-based CMOS cameras operating in the visible range. MIR imaging experiments were designed (Figure 22A), where a thin layer of sputtered indium-tin-oxide (ITO) adopting a shape of letter “E” was placed in front of a PEA fdm on glass substrate. Regions of the ITO fdm can effectively block the MIR pump light at 3.3 pm (Figure 23) due to the Drude response of free carriers and the associated negative real part of relative permittivity. The MIR pump was chopped at 125 Hz, and the pump-induced reflectivity change was captured by the camera at a 250-Hz frame rate, with a field of view of approximately 200*400 pm2. Note that the imaging resolution is determined by the diffraction limit of the visible probe rather than the MIR light. The designed ITO pattern on PEA observed under brightfield in reflection is shown in Figure 22B, in conjunction with the acquired image of AR / R induced by MIR irlight. The results demonstrate that spin-coated PEA films feature good uniformity in MIR-induced response over large areas and suggest that 2D-MHPs can be further conceived for building MIR imagers and cameras.

[0207] Maximizing the sensitivity of single-channel MIR detectors

[0208] Two strategies are utilized to enhance the responsivity of MIR detection. The first strategy involves eliminating the PET substrate that was utilized previously, as shown in Figure 7 and Figure 11. Instead, a floating, single-crystalline membranes of (PEA)2Pbl4 is employed. By opting for a substrate-less membrane, maximize heat retention can be maximized, while taking advantage of the layered structure of 2D perovskites that naturally facilitate the growth of freestanding membranes. To illustrate the benefits of this approach, the simulated temperature decay profiles in Figure 24 demonstrate the behavior of a floating (PEA)2Pbl4 membrane with 1 pm thickness, following an impulsive MIR excitation. The MIR pulse is characterized by a Gaussian spatial profile with a beam radius of 10 pm. Comparing this to the 1 pm-thick (PEA)2Pbl4 films deposited on PET and Si substrates, where heat gradually dissipates into the semi-infinite substrates, lateral heat diffusion in the (PEA)2Pbl4 membrane is approximately an order of magnitude slower. This slowdown in heat diffusion is expected to enhance the sensitivity, reaching levels of 100 pW pm’2, a substantial improvement over the 1 nW pm'2achieved previously. Furthermore, when subjected to continuous MIR illumination, the temperature rise in the (PEA)2Pbl4 membrane is influenced by a balance between heat accumulation and diffusion. Heat-transport simulations with continuous MIR excitation, as shown in Figure 24C, demonstrate that the temperature rise in the (PEA)2Pbl4 membrane primarily occurs within the initial several milliseconds. Unlike substrate-supported structures, the temperature rise of the (PEA)2Pbl4 membrane is also dependent on the spot size of the MIR beam. As illustrated in Figure 25, when the radius of the MIR beam increases from 10 pm to 50 pm, a further slowdown of heat dissipation is observed within the (PEA)2Pbl4 membrane by an additional order of magnitude. When considering an infinitely large (PEA)2Pbl4 membrane under uniform MIR illumination, the sole heat dissipation pathway is through radiation rather than conduction. Practically, for a (PEA)2Pbl4 membrane under structure-less MIR illumination, the MIR beam is not intentionally focused (z.e., spot size > 50 pm), which offers another order of magnitude enhancement in sensitivity (from 100 pW pm’2to 10 pW pm'2) as compared to Figure 24.

[0209] The second strategy involves leveraging the nontrivial phase shift that occurs at the interface between the optically lossy (PEA)2Pbl4, particularly near its exciton resonance, and a lossless dielectric material such as AI2O3 or SiCh. These dielectric materials can be deposited onto (PEA)2Pbl4 membranes straightforwardly by electron-beam evaporation. The interference effect resulting from this nontrivial phase shift can modify the reflectance characteristics around the exciton resonance (see Figure 26) and, importantly, lead to a near-zero reflectivity for certain coating thicknesses (e.g, when the coating thickness is 40 nm or 50 nm, less than a quarter of the wavelength). In fact, the modulation in reflectance near the exciton resonance is periodic with respect to coating thickness, as illustrated in Figure 27A. A lower steady-state reflectivity is desirable since it enhances the relative change in reflectance ( RR / RR), which is the signal readout in the proposed all-optical MIR detection scheme. Under an increase in the lattice temperature (accompanied by an increase in the exciton damping factor y), ARR / RR diverges when the steady-state reflectivity approaches zero (see Figure 27B and Figure 27C). The enhancement factor of ARR / RR, defined as the ratio of RR / RR obtained with a certain coating thickness to RR / RR obtained without any coating, also diverges. In practical situations, the divergent enhancement in ARR / RR and, consequently, the MIR sensitivity will be offset by crystal surface roughness and local variations in coating thickness, deviating from the specific conditions depicted in Figure 27B and Figure 27D. Nevertheless, by conservatively assuming a tenfold enhancement in ARR / RR through the dielectric coating strategy, we can increase the sensitivity from 10 pW ym’2to the targeted level of 1 pW pm'2.

[0210] Incorporating these two strategies, Figure 28A depicts the design of the single-channel MIR detector and imager based on (PEA)2Pbl4 membranes. The (PEA)2Pbl4 membranes, approximately 1 pm thick, are synthesized using the space-confined approach (Chen, Y.-X., et al., 2016, Journal of the American Chemical Society, 138: 16196-16199; Chen, Z., et al., 2017, Nature Communications, 8:1890). The top layer consists of AI2O3, serving as the dielectric coating to enhance sensitivity. This layer is grown using electron-beam evaporation. The MIR light absorber comprises a bottom TCO film. Two types of TCOs, namely ICO and ITO, are employed (Sachet, E., et al., 2015, Nature Materials, 14:414-420; Guo, P., et al., 2016, Nature Photonics, 10:267-273). The ICO films are deposited using pulsed laser deposition (PLD) at ambient temperature. Both PLD and ion beam deposition provide uniform film growth over at least centimeter length-scales.

[0211] MIR light by TCO films occurs at the Ferrell-Berreman modes, which are near the epsilon-near-zero regime of the TCOs (Guo, P., et al., 2018, ACS Photonics, 5:2000-2007; Newman, W. D., et al., 2015, ACS Photonics, 2:2-7; Ferrell, R. A., 1958, Physical Review, 111 : 1214-1222). The permittivity of TCOs in the MIR can be accurately described using the Drude model, expressed as £'(m) (m2+i<Dy), where o>Prepresents the plasma frequency and y is the damping factor of the free electrons. Figure 28B illustrates the correlation between a>p and the spectral location of MIR absorption by the TCO films. By adjusting within the range of 0.4 eV and 1 .0 eV, it is possible to achieve significant MIR absorption, ranging from 60% to 90% over a wavelength of 2 pm and 6 pm.

[0212] To establish lookup tables correlating growth conditions with the concentration and mobility of free electrons in ICO and ITO films, these films are initially deposited on glass and Si substrates using varying oxygen flow rates. MIR transmittance of the TCO films is measured using Fourier-transform infrared spectroscopy (FTIR) to derive the a)Pand y of the films for accurately designing the spectral response of the MIR detectors.

[0213] Once reproducible recipes are established, ICO and ITO films are grown with thicknesses of 150-200 nm on the back side of the (PEA)2Pbl4 membranes. Samples are fabricated using TCO films with varying plasma frequencies to achieve detectors with peak sensitivity between 2 pm to 5 pm, with an increment of 1 pm. These tri-layer device stacks are mounted onto Si wafers with periodically spaced holes. The holes are created through standard photolithography, followed by chromium (Cr) deposition and deep reactive ion etching (RTE), resulting in hole depths of 100-200 pm. For single-channel MIR detectors, the hole diameters range from 100-200 pm. Conversely, for MIR imagers, the hole diameter is in the 20-50 pm range. Each tri-layer confined within a hole is treated as an individual pixel, as the (PEA)2Pbl4 membranes in neighboring holes are largely thermally decoupled.

[0214] Fabricating wavelength-multiplexed MIR and THz imagers

[0215] Based on the sensitive MIR detectors, the next objective was to implement imagers with controlled variations in spectral response along a ID axis. To achieve this, gold bowtie nanoantennas are used as the MIR light absorbers, replacing the TCO films. Unlike the spatially uniform TCO films, the plasmonic gold bowtie antennas are capable of concentrating electric fields at the gaps, thereby enhancing local absorption of MIR light and increasing the local temperature rise in the (PEA)2Pbl4 membrane. However, the membrane structure is incompatible with conventional photolithography methods (e.g, spin-coating photoresist onto the membranes becomes challenging). Therefore, a method known as PEEL (photolithography, etching, electron-beam deposition, and lift-off) is employed to fabricate large-area gold bowtie structures (Henzie, J., et al., 2006, Accounts of Chemical Research, 39:249-257; Henzie, J., et al., 2007, Nature Nanotechnology, 2:549-554; Wang, D., et al., 2015, ACS Photonics, 2: 1789-1794). This method allows precise control over the size and geometry of each individual bowtie. SAs illustrated in Figure 29, the PEEL process involves several steps: 1) beginning with a Si wafer, the desired pattern from the photomask is transferred onto the photoresist on the Si surface; 2) after development, the photoresist that remains on the Si adopts the bowtie shape; 3) a layer of Cr is deposited on the sample, and a lift-off process is carried out, resulting in a reverse-bowtie structure of Cr on Si; 4) deep RIE is performed to create deep holes in the Si regions that are not protected by the Cr layer; 5) gold is evaporated onto the sample; 6) by selectively etching the Cr, a free-standing gold fdm is obtained, which can then be transferred onto the (PEA)2Pbl4 membrane. The gold film then serves as a shadow mask for a subsequent gold evaporation step. Finally, the gold membrane is peeled off, leaving behind the desired gold bowtie pattern on the (PEA)2Pbl4 membrane. The advantage of the PEEL process is that it requires only one lithography step, eliminating the need for pattern registration. The fabrication process is highly scalable and can provide high yields.

[0216] For the LWIR wavelengths, bowties are designed with dimensions suitable for photolithography, where the smallest feature size will be approximately 1 pm. For the MWIR range, which involves smaller feature sizes, specialized nanostructures with feature sizes down to 100 nm are utilized (Yang, A., et al., 2016, Proceedings of the National Academy of Sciences USA, 113: 14201-14206; Rawashedh, A., et al., 2023, Nano Letters, 23:469-475). Periodic gold nanoparticles and gold nanogratings serve as alternative structures to gold bowtie antennas to provide tailorable MIR absorption resonances, offering additional design and fabrication flexibilities (Hua, Y., et al., 2019, ACS Photonics, 6:322-326). The geometric parameters of the gold bowties are determined through finite-difference time domain (FDTD) simulations (i.e., Lumerical FDTD) to achieve tunable MIR absorption. Preliminary simulation results (see Figure 30) indicate that gold bowtie antennas with a thickness of 30 nm can be designed to exhibit tunable and effective MIR absorption.

[0217] MIR imagers are fabricated using gold bowtie antenna-decorated (PEA)2Pbl4 membranes with areas exceeding 2 mm * 2 mm. Each individual pixel is a sub-area on the imager with a desirable spectral bandwidth. A pixel is defined by a hole on the Si and will have a size of 50 pm x 50 pm, resulting in a total pixel count of 40 x 40. Larger pixel counts are achieved by stitching multiple (PEA)2Pbl4 membranes on the Si wafer. Concurrently, MIR metasurfaces are designed and fabricated, acting as miniature grating for spectral splitting. The spectral dispersion of the MIR light caused by the metasurfaces aligns with the spectral response of the MIR imagers, enabling spectral intensity characterization. The targeted spectral coverage of the imagers is from 3 pm to 12 pm, although this entire range may not be achieved on the same (PEA)2Pbl4 membrane.

[0218] Leveraging the ultralow K and the large exciton-induced TCR (two properties that are rarely available together) of 2D-MHPs, a previously uncharted application of these materials was demonstrated in MIR “thermal” detection using (PEA)2Pbl4 as a prototypical 2D-MHP. Shown in Table 2 is a comparison of this 2D-MHP-basec scheme demonstrating the favorability of the instant scheme over other methods for broadband MIR detection. Other emerging hybrid layered materials, which may offer lower thermal conductivity and higher TCR are being investigated for potential additional advancements in MIR detectivity (Paritmongkol, W., et al., 2021, Journal of the American Chemical Society, 143:20256-20263; Li, W., et al., 2017, Nature Reviews Materials, 2(3): 16099). Ongoing experiments are investigating the use of this scheme in MIR imagers with lithographically? defined 2D arrays of SiNx membrane windows. Multiplexed MIR detection with both intensity and wavelength information by lithographically fabricating pixelated plasmonic nano-antennas and employing TCO NC pads with different doping concentrations using ink-jet printing are both being investigated. Extended light detection into the far-infrared and the terahertz range is being investigated with 2D-MHPs interfaced with optical resonators exhibiting strong plasmonic or phononic absorption at those spectral ranges (Liu, M., et al., 2012, Nature, 487:345-348; Caldwell, J. D., et al., 2016, Nature Nanotechnology, 11:9-15; Dai, S., et al., 2015, Nature Nanotechnology, 10:682-686; Wang, C., et al., 2020, Nature Communications, 11 : 1158).

[0219] The methods employed are described herein.

[0220] Sample Fabrication and Structural Characterization Materials: Lead (II) iodide (99.999%) and ^-butyrolactone (>99%) were obtained from

[0221] Sigma-Aldrich; phenethylammonium iodide was obtained from Greatcell Solar. All chemicals were used as received.

[0222] Synthesis'. The perovskite thin films were fabricated by a two-step spin-coating method in ambient conditions. Specifically, the perovskite precursor solution was prepared by dissolving 0.9 mmol of lead (II) iodide and 1.8 mmol of phenylethylammonium iodide into 0.54 mL of y- butyrolactone. The substrates were treated with air plasma for 10 mins to ensure good solution wettability. The perovskite films were fabricated by dropping 50 pL of precursor solution onto the substrates and going through a two-step spin-coating program with 1000 rpm for 5 s and 3000 rpm for 45 s. Subsequently, the film was annealed at 80 °C on a hot plate for 15 mins. Structural characterization: The crystalline orientations of the perovskite films on various substrates were measured by X-ray diffraction (XRD) using ()-20 scans with a Rigaku SmartLab® X-ray diffractometer. The film thickness, morphology, and interfacial quality of multilayer stacks were examined by scanning electron microscopy (Hitachi SU8230). The images of the nanocrystals were acquired by a JEOL 21 OOF transmission electron microscope operated at 200 kV with a 60,000 x magnification.

[0223] Nanocrystal Synthesis and ITO Film Growth

[0224] Materials: Cadmium acetyl acetonate (99.9%), indium fluoride (99.9%), indium acetate (99.99%), octadecene (90%), and oleic acid (90%) were obtained from Sigma-Aldrich and used as received. Isopropanol and toluene for washing the particles were ACS grade from Fisher.

[0225] Synthesis'. Colloidal nanocrystals of doped cadmium oxide were prepared following literature procedures with small modifications (Gordin, T. R., et al., 2013, Nano Letters, 13:2857-2863; Ye, X., et al., 2014, Journal of the American Chemical Society, 136: 11680- 11686; Diroll, B. T., et al., 2014, Chemistry of Materials, 26:4579-4588). All reactions consisted of 25 mL of octadecene, 1 mL oleic acid, and 1 mmol of total metal precursors; the precursors were loaded into a three-neck, 50 mL reaction flask and heated to 120 °C and held for 1 hour under vacuum (~1 torr), then heated rapidly under nitrogen atmosphere to the boiling point (-316 °C). The reaction was held at the boiling point of the solution for times between 5 and 40 minutes before the reaction medium turned from colorless to brown or green. After this color change, the reaction was maintained at 316 °C for an additional 10 minutes before being cooled back to room temperature by removal of a heating mantle. At room temperature, the reaction was decanted into centrifuge tubes, and 10 mL of toluene was added and enough isopropanol to induce flocculation of the particles. The samples were centrifuged for 5 minutes at 4000 rpm. Then, the pallet was re-dispersed in 5 mL of toluene. The solution was flocculated again with additional isopropanol and centrifuged for 5 minutes at 4000 rpm. The resulting pellet was redispersed in 3 mL of toluene and centrifuged at 2000 rpm for 2 minutes. The supernatant was saved. After one week, the solution was filtered through a 0.45 micrometer Teflon filter to remove precipitates. To change the frequency of the localized surface plasmon resonance, the type and amount of doping was controlled through the input metal precursors. Cadmium acetyl aceton ate was used as the cadmium precursor for 80% to 99% of the total metal content. Indium doping was achieved using between 1% and 20% indium acetate. Indium and fluorine co-doping was achieved by adding between 8% and 20% indium fluoride. The indium acetate doping concentrations in ICO-1 and ICO-2 were 20% and 5%, respectively. The indium fluoride doping concentration of FICO was 15%. The ITO film serving as the mask for blocking MIR light (Figure 22B) was deposited at room temperature using a physical vapor sputter / thermal evaporator system (Kurt J. Lesker Co.® PVD75). An ITO sputtering target of In203 / Sn02=90 / 10 wt% was used. The experiments were conducted at a pressure of 6.9 mTorr under high-purity argon flow with a growth rate of 0.03-0.04 nm / second.

[0226] Finite-Element Simulations of Heat Transfer

[0227] The Heat Transfer module available in COMSOL Multiphysics® 5.3a was used to simulate the transient thermal transport process along the cross-plane direction for comparison with experimental data. The calculation was performed in the time domain by solving the equation of heat conduction (z.e., Fourier’s law; Equation 4), where p is the mass density, CPis the specific heat capacity, K is the thermal conductivity, and T is the lattice temperature.

[0228] (Equation 4)

[0229] The heat capacity and thermal conductivity for silicon wafer were taken to be 710 J kg'1K'1and 142.2 W m-1K'1, respectively. The thermal conductivity and heat capacity of polyethylene terephthalate (PET) were taken to be 0.19 W m’1K’1and 1000 J kg-1K-1, respectively. The density, heat capacity, and thermal conductivity for cadmium oxide were taken from literature as 8101.4 kg m’3, 43.1 J mol-1K-1(or equivalently 335.6 J kg'1K’1), and 5.6-9.3 W m-1K-1, respectively (Millar, R. W., 1928, Journal of the American Chemical Society, 50:2653-2656; Lindsay, L. & Parker, D. S., 2015, Physical Review B, 92: 144301). The heat capacity of the TCO films was calculated by using a volume filling ratio of 41% for the inorganic core, 23% for the organic ligands, and 36% for the empty space between the particles. Such volume filling ratios were estimated by assuming that the inorganic core has a spherical shape with a diameter of 9.5 nm, the oleic ligands have a length of 1.5 nm, and the particles are randomly close-packed (i.e., empty space between the particles occupies a volume fraction of 36%). The heat capacity (Cedeno, F. O., et al., 2000, Journal of Chemical Engineering Data, 45:64-69) and mass density for oleic acid at 298 K were taken to be 1950 J kg-1K-1and 895 kg m-3, respectively. The heat capacity and mass density of the TCO film were determined to be 429.8 J kg-1K-1and 3527.4 kg m’3, respectively (by weighted sums of the inorganic and organic components comprising the film).

[0230] When simulating the ICO / PEA / substrate stack, a uniform temperature rise of 10 K at time zero was assumed for the ICO film, whereas the initial temperature rise in PEA was taken to be zero, since the MIR absorption of ICO is about an order of magnitude higher than PEA. When simulating the PEA / substrate stack (i.e., no ICO), the initial temperature in PEA peaked at the surface and decayed exponentially along the depth following the Beer-Lambert law. The absorption coefficient of the MIR pump in the PEA film was determined to be 6140 cm'1using the data shown in Figure 7C. In accordance with the penetration depth of the probe at -500 nm (-140 nm; Figure 2), the temperature of the top 140-nm thickness of the PEA film from the simulations was averaged, the normalized temporal decay of which was compared with the normalized, experimental R / R at -500 nm. It is to be noted that in the small temperature perturbation regime of the transient reflection experiments (as indicated by the fluenceindependent decay kinetics; Figure 23), the R / R scales linearly with the lattice temperature, justifying the direct comparison between the simulated temperature decay and the measured A / ? / / ?.

[0231] Steady-State Optical Characterization

[0232] The steady-state optical reflectance experiments were performed using a customized micro-reflectance spectroscopy setup as reported previously (Li, S., et al., 2022, Physical Review Letters, 129: 177401), with a slight modification that the light source was replaced by a supercontinuum laser (DISCO-2-UV, Leukos). A liquid-nitrogen cryostat (VPF-100, Lake Shore) was used to vary the sample’s temperature from 78 to 300 K at a vacuum condition better than 1 x 10’4Torr. The MIR transmittance spectra were measured by Fourier-transform infrared spectroscopy (Nicolet 6700 FT-IR) with a mercury-cadmium-telluride detector.

[0233] Infrared-Pump Visible-Probe (IPVP) Transient Reflection (TR) Experiments

[0234] The IPVP TR measurements with a ns-to-ms time window were based on a setup reported previously (Li, S., et al., 2022, Review of Scientific Instruments, 93:053003; Li, S., et al., 2023, Matter, 6:460-474). Briefly, the idler output from a high-energy mid-infrared (MIR) optical parametric amplifier (OP A; Orpheus-ONE-HE, Light Conversion) served as the pump. The OPA was powered by a 170-fs Yb:KGW laser amplifier (Pharos, Light Conversion) with 0.9 mJ input energy operated at 2 kHz repetition rate and reduced into 1 kHz by an optical chopper. The broadband probe pulses at 2 kHz repetition rate were produced by a supercontinuum laser (DISCO-2 -UV, Leukos), which was electronically triggered and delayed from the fs pump laser with a digital delay generator (DG645, Stanford Research Systems). The pump pulse was focused onto the sample using a CaF2 lens of 200 mm focal length, which yielded a spot size of -220 pm in diameter. The probe pulse was focused onto the sample using a 100 mm focal- length, achromatic doublet lens, providing a spot size of -50 pm in diameter. The reflected probe pulses were captured and processed with a USB-coupled CMOS spectrometer (AvaSpec- ULS2048CL-EVO, Avantes).

[0235] Heat Capacity Calculations

[0236] The crystal structure of PEA is taken from the literature (Du, K.-Z., et al., 2017, Inorganic Chemistry, 56:9291-9302) with a molecular weight of 959.19 g em-3. The heat capacity of bulk PEA was computed using first-principles simulations. The approach involved performing structure relaxation and self-consistent density-functional-theory (DFT) calculations using the Vienna Ab initio Simulation Package (VASP) (Kresse, G. & Hafner, J., 1993, Physical Review B, 47:558-561; Kresse, G. & Hafner, J., 1994, Physical Review B, 49: 14251-14269; Kresse, G & Furthmuller, J., 1996, Computational Materials Science, 6: 15-50; Kresse, G & Furthmuller, J., 1996, Physical Review B, 54: 11169-11186). The projector-augmented wave (PAW) method in conjunction with the vdW-DF2 exchange-correlation functional were employed (Blbchl, P. E., 1994, Physical Review B, 50: 17953-17979; Lee, K., et al., 2010, Physical Review B, 82:081101). Structure relaxations of the primitive cell of PEA were performed using Gamma-centered k-point meshes with the smallest allowed spacing of 0.3 A'1between the k points, while adopting a kinetic energy cutoff of 520 eV. The force and energy convergence thresholds were set to be 10'3eV- A'1and 10'7eV, respectively. The phonons and temperature-dependent heat capacities were computed using the Phonopy software (Togo, A. & Tanaka, I., 2015, Sripta Materiala, 108: 1-5) with a supercell size of I x l x l composed of 188 atoms in total.

[0237] All-Optical MIR Detection Measurements A MIR supercontinuum laser (SC4500, Thorlabs) was used as the MIR light source, which offers broadband output from 2.2 pm to 4.2 pm at a repetition rate of ~50 MHz. Compared to the thermal response time of the sample (z.e., tens of ps; Figure IF) and the optical chopper frequency (100-5000 Hz), the MIR laser can be treated as a continuous-wave source. Several MIR bandpass fdters (FB1900-200, FB3250-500, FB3330-150, FB3750-500, and FB4000-500, all from Thorlabs) were used to select the wavelength of the MIR light incident on the sample. The measured transmission spectra of the MIR fdters are plotted in Figure 12. An optical chopper was used to turn on and off the MIR beam at a frequency of 100 Hz, unless otherwise specified. A CaF2 lens was used to focus the MIR laser onto the sample with a spot size of 90 pm in diameter. A neutral-density filter wheel was used to vary the power of the MIR laser incident on the sample.

[0238] The samples were probed by a high-power green light-emitting diode (LED) source (SOLIS-505C, Thorlabs). The output from the LED was wavelength-filtered by a 500-nm bandpass filter (10BPF10-500, Newport) or a 510-nm bandpass filter (FBH510-10, Thorlabs). The probe-light reflected by the sample was directed into a photomultiplier tube (Hl 0722-20, Hamamatsu), whose voltage output was measured by a lock-in amplifier (SR860, Stanford Research Systems) with the optical chopper providing the reference signal. The control voltage of the PMT was adjusted to yield a constant output voltage (-0.5 volts) throughout the measurements to enable comparison between different samples.

[0239] Optical Pump-Probe Imaging Measurements

[0240] The pump pulses were produced from the MIR OPA (the same as that used in the TR experiments) and focused onto the sample using a CaF2 lens (Figure 22E). A mask made of patterned indium-tin-oxide film was used to partially block the MIR beam impinging on the sample. The monochromatic probe pulses were produced from a supercontinuum laser (NKT Compact; 1-2 ns pulse width) and an acousto-optic tunable filter (NKT SuperK SELECT). The probe laser was electronically delayed from the pump by a digital delay generator (DG645) and was directed onto the sample using a microscope objective (5*, 0.14 NA, Mitutoyo). The probe light reflected off the sample was directed to and imaged by a CMOS camera (PixeLINK PL- 0753). The camera was synced with the pump laser but was operated at a reduced framerate of 250 Hz. An optical chopper operating at 125 Hz was used to turn on and off the pump light. By performing heat transport simulations, we compare the heat dissipation rates of a suspended Si pad, the geometry of which is taken from literature, and a 1-pm thick PEA thin film deposited on a PET substrate. An impulsive temperature increase of the Si pad and the PEA film is introduced at zero time. Although the Si pad (250 nm thick) is thinner than the PEA layer, the three orders-of-magnitude lower K of PEA can also constrain in-plane heat spreading, in addition to slowing down the vertical heat flow.

[0241] The disclosures of each and every patent, patent application, and publication cited herein are hereby incorporated herein by reference in their entirety. While this invention has been disclosed with reference to specific embodiments, it is apparent that other embodiments and variations of this invention may be devised by others skilled in the art without departing from the true spirit and scope of the invention. The appended claims are intended to be construed to include all such embodiments and equivalent variations.

Claims

CLAIMSWhat is claimed is:

1. A thin-layer device for detection of mid-infrared light (MIR) comprising a layer of a metal halide perovskite (MHP) fdm on a substrate layer, wherein the substrate layer comprises a low-thermal conductivity polymer or a thin inorganic membrane.

2. The device of claim 1, wherein the MHP comprises a lead halide and an ammonium salt.

3. The device of claim 2, wherein the lead halide is selected from PbCl2, PbBr2, and Pbl2.

4. The device of claim 2, wherein the ammonium salt is selected from the group consisting of MeNHiCl, MeNH3Br, MeNH3I, EtNH3Cl, EtNH3Br, EtNH3I, n-PrNHsCl, n- PrNH3Br, n-PrNH3I, i-PrNH3Cl, i-PrNH3Br, i-PrNH3I, n-BuNH3Cl, n-BuNH3Br, n-BuNH3I, i- BuNHsCl, i-BuNH3Br, i-BuNEM, s-BuNH3Cl, s-BuNH3Br, s-BuNHsI, t-BuNH3Cl, t-BuNH3Br, t-BuNH3I, PhCH2NH3Cl, PhCH2NH3Br, PhCH2NH3I, PhCH2CH2NH3Cl, PhCH2CH2NH3Br, PhCH2CH2NH3I, PhCH2CH2CH2NH3Cl, PhCH2CH2CH2NH3Br, and PhCH2CH2CH2NH3I.

5. The device of claim 4, wherein the MHP is (PhCH2CH2NH3)2Pbl46. The device of claim 1, wherein the low-thermal conductivity polymer has a thermal conductivity less than about 0.25 W m’1K’1.

7. The device of claim 6, wherein the low-thermal conductivity polymer is one or more selected from the group consisting of nylon-6 (PA6), polyetheretherketone (PEEK), polytetrafluoroethylene (PTFE), poly (dimethyl siloxane) (PDMS), polysulfone (PSU), polymethylmethacrylate (PMMA), polycarbonate (PC), polyvinylchloride (PVC), polyvinylidene difluoride (PVDF), polyethylene terephthalate (PET), polystyrene (PS), polypropylene (PP), polyethylene (PE), and polyimide (PI).

8. The device of claim 7, wherein the low-thermal conductivity polymer is PET.

9. The device of claim 7, wherein the MHP is (PhCH2CH2NHs)2Pbl4.

10. The device of claim 9, wherein a thickness of the MHP layer is between 100 nm and 10,000 nm.

11. The device of claim 10, wherein the thickness of the MHP layer is between 500 nm and 1,000 nm.

12. The device of claim 11, wherein the thickness of the MHP layer is about 940 nm.

13. The device of claim 9, wherein the device further comprises an enhancement layer comprising infrared-absorbing nanocrystals on the MHP face opposite the PET.

14. The device of claim 13, wherein the infrared-absorbing nanocrystals comprise cadmium oxide (CdO).

15. The device of claim 14, wherein the infrared-absorbing nanocrystals further comprises one or more dopants selected from the group consisting of indium, fluorine, gold, silver, and aluminum.

16. The device of claim 15, wherein a thickness of the enhancement layer is between 100 nm and 300 nm.

17. The device of claim 16, wherein the thickness of the enhancement layer is about 150 nm.

18. The device of claim 13, wherein the device further comprises a barrier layer comprising aluminum oxide (AI2O3) between the MHP layer and the enhancement layer.

19. The device of claim 1 , wherein the substrate layer comprises a thin inorganic membrane comprising one or more selected from the group consisting of aluminum oxide, silicon oxide, aluminum nitride, and silicon nitride.

20. The device of claim 19, wherein the inorganic membrane comprises silicon nitride.

21. The device of claim 20, wherein the device further comprises a support layer on the silicon nitride face opposite the MHP layer.

22. The device of claim 21, wherein the support layer comprises silicon.

23. The device of claim 22, wherein the support layer comprises at least one opening exposing the surface of the silicon nitride.

24. The device of claim 23, wherein the MHP is (PhCH2CH2NH3)2Pbl4.

25. The device of claim 24, wherein a thickness of the MHP layer is between 100 nm and 10,000 nm.

26. The device of claim 25, wherein the thickness of the MHP layer is between 500 nm and 1,000 nm.

27. The device of claim 26, wherein the thickness of the MHP layer is about 940 nm.

28. The device of claim 27, wherein the device further comprises an enhancement layer comprising infrared-absorbing nanocrystals.

29. The device of claim 28, wherein the infrared-absorbing nanocrystals comprise cadmium oxide (CdO).

30. The device of claim 29, wherein the infrared-absorbing nanocrystals further comprise one or more dopants selected from the group consisting of indium, fluorine, gold, silver, and aluminum.

31. The device of claim 30, wherein a thickness of the enhancement layer is between 100 nm and 300 nm.

32. The device of claim 31, wherein the thickness of the enhancement layer is about 150 nm.

33. The device of claim 28, wherein the enhancement layer is on the MHP face opposite the silicon nitride.

34. The device of claim 28, wherein the enhancement layer is on the exposed surface of the silicon nitride.

35. The device of claim 32, wherein the device further comprises a second substrate layer comprising silicon nitride on the support face opposite the first layer of silicon nitride.

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