Perovskite band-pass photodetector for weak light detection
By constructing a lattice-matched perovskite heterojunction and a Type-II bandgap arrangement, the problem of insufficient signal-to-noise ratio of existing photodetectors under nanowatt-level low light conditions was solved, realizing a filterless self-driven bandpass photodetector with high sensitivity and long-term stability.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- NANJING UNIV OF AERONAUTICS & ASTRONAUTICS
- Filing Date
- 2026-03-17
- Publication Date
- 2026-06-26
AI Technical Summary
Existing photodetectors cannot meet the signal-to-noise ratio requirements under low light conditions at the nanowatt level. They mostly rely on external bias voltage to operate and cannot achieve zero-power self-driven mode. Furthermore, they suffer from material defects and carrier recombination problems, which limit their application in portable and long-distance sensing systems.
By selecting perovskite materials with a lattice mismatch of less than 5% to construct a high-quality heterostructure, a Type-II bandgap arrangement is formed, achieving efficient carrier separation under zero bias voltage. Combined with the CCN mechanism, a filterless bandpass photodetector is realized.
It achieves low defect density and high sensitivity self-driven weak light detection, has nanowatt-level photocurrent response, good long-term stability, is suitable for self-driven operation mode, and simplifies device structure.
Smart Images
Figure CN122294697A_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of photoelectric detection technology, specifically relating to a perovskite bandpass photodetector for weak light detection, which is particularly suitable for photoelectric sensing systems in self-driven operating mode and nanowatt-level weak light detection scenarios. Background Technology
[0002] With the rapid development of IoT, machine vision, deep-sea optical communication, and biomedical imaging technologies, the requirements for photodetectors have shifted from simple light intensity detection to spectrally selective detection with higher resolution. Especially in applications such as multi-channel secure communication, specific-band fluorescence detection, and portable sensing devices, detectors capable of accurately responding to specific band signals, suppressing background noise interference, and operating with low or even zero power consumption have become core components for building high signal-to-noise ratio sensing systems.
[0003] Traditional spectrally selective detectors typically rely on external optical filters to achieve wavelength selection, which not only increases the system's size and complexity but also introduces additional optical losses and manufacturing costs. In recent years, filterless narrowband detectors based on charge collection narrowing (CCN) mechanisms have attracted widespread attention due to their simple structure and ease of integration. However, existing CCN mechanism detectors are mainly based on polycrystalline thin-film materials, which contain numerous grain boundaries and deep-level traps, making carriers susceptible to capture and recombination during transport, severely limiting device performance. Furthermore, to achieve effective carrier extraction, a high reverse bias voltage is usually required, increasing system power consumption, and the high electric field easily induces ion migration problems in perovskite materials, affecting device stability. Limited by material quality and dark current levels, the signal-to-noise ratio of existing devices under nanowatt-level weak light conditions is insufficient to meet the requirements for weak signal detection such as fluorescence detection and deep-sea communication. Most devices rely on external bias voltages for operation and cannot achieve zero-power self-driven detection modes, limiting their application in portable, implantable, and long-distance sensing systems. Therefore, developing a filterless bandpass photodetector that combines low defect density, high sensitivity, weak light detection capability, and self-driven operation is of great scientific significance and application value. Summary of the Invention
[0004] To address the shortcomings of existing technologies, the present invention aims to provide a perovskite bandpass photodetector for weak light detection. By selecting a combination of perovskite materials with appropriate lattice mismatch, a high-quality heterojunction is constructed. The Type-II band arrangement formed at the interface is used to achieve efficient carrier separation under zero bias, thereby obtaining a self-driven bandpass photodetector with weak light detection capability without the need for an external filter.
[0005] To achieve the above objectives, the present invention provides the following technical solution: a perovskite bandpass photodetector for weak light detection, characterized in that it comprises: a transparent conductive substrate, a first perovskite single crystal substrate layer formed on the transparent conductive substrate, the first perovskite material having a first band gap and a first lattice constant, a second perovskite single crystal epitaxial layer formed on the first perovskite single crystal substrate layer, the second perovskite material having a second band gap and a second lattice constant, wherein the second band gap is smaller than the first band gap, and a back electrode formed on the second perovskite single crystal epitaxial layer.
[0006] The first perovskite material and the second perovskite material have the same or similar crystal structures, and the lattice mismatch between them is less than 5%, preferably less than 3%, and more preferably 1.5% to 2.5%, so that a high-quality coherent or semi-coherent heterostructure is formed between them, with an interface defect density of less than 10. 13 cm -3 .
[0007] The thickness of the first perovskite single crystal substrate is configured to achieve charge collection narrowing self-filtering for short-wavelength photons with energies greater than the first bandgap, i.e., the thickness is sufficient to allow photogenerated carriers generated by short-wavelength photons on the substrate surface to recombine and quench before reaching the heterojunction interface.
[0008] The thickness of the second perovskite single-crystal epitaxial layer is configured to fully absorb target band photons with energy between the first bandgap and the second bandgap.
[0009] The first perovskite material and the second calcareous material form a Type-II band arrangement, i.e., the conduction band bottom energy level difference ΔE. c ≤0.05eV, valence band top energy level difference ΔE v ≥0.5eV enables the generation of a built-in electric field at the interface under zero bias, achieving self-driven separation of photogenerated carriers.
[0010] Compared with the prior art, the advantages of the present invention are as follows:
[0011] (1) This invention selects a first perovskite and a second perovskite with a lattice mismatch of less than 5% to construct a heterojunction. Both have the same crystal structure, similar lattice constants, and similar atomic arrangements. This lattice matching characteristic results in low lattice stress at the interface during epitaxial growth, facilitating the formation of coherent or semi-coherent interfaces, and significantly reducing the density of mismatched dislocations and dangling bonds at the interface. SCLC testing shows that the defect density of the epitaxial layer can be as low as 10-1. 12 ~10 13 cm -3 The defect density is on the order of magnitude lower than that of traditional polycrystalline heterostructures, by 2-3 orders of magnitude. The low defect density effectively suppresses nonradiative recombination of charge carriers, ensuring efficient transport of photogenerated charge carriers.
[0012] (2) Furthermore, by adjusting the thickness of the first perovskite single crystal layer to be much greater than the penetration depth of short-wavelength photons, the surface recombination quenching of short-wavelength photogenerated carriers is achieved using the CCN mechanism, while long-wavelength photons can penetrate deep into the crystal and be collected, thus achieving intrinsic spectral selectivity without the use of an external filter. The band gap of the first perovskite single crystal layer determines the opening wavelength of the detection window, and the band gap of the second perovskite single crystal layer determines the cutoff wavelength of the detection window. The two work together to form a natural bandpass response characteristic, which greatly simplifies the device structure.
[0013] (3) Due to the good lattice matching of the two materials and the low defect state density at the interface, the Type-II band structure can be fully utilized. The near-aligned conduction band bottoms provide a barrier-free transport channel for photogenerated electrons, while the valence band tops are significantly offset, forming a hole-blocking barrier. This band configuration creates a built-in electric field at the interface, enabling the device to achieve spontaneous separation of photogenerated carriers even at zero bias. Simultaneously, thanks to the low-defect interface, the recombination loss of photogenerated carriers during transport is small, with the device achieving a minimum recombination rate of 0.53 μW / cm². 2 Even with nanowatt-level weak light, it can still produce a clearly discernible photocurrent response, with a detectivity of 3×10⁻⁶. 9 Jones and above achieved low-light self-driven detection.
[0014] (4) The all-monocrystalline material system used in this invention completely eliminates grain boundary defects commonly found in polycrystalline thin films, effectively blocks ion migration paths, and suppresses performance degradation under the influence of an electric field. The device exhibits good long-term operational stability with a photocurrent attenuation of less than 2% under continuous periodic illumination for several hours. Attached Figure Description
[0015] Figure 1 This is a schematic diagram of the detector's structure.
[0016] Figure 2 The UV-Vis absorption spectrum, steady-state photoluminescence spectrum, and TRPL curve are for Example 1.
[0017] Figure 3 The ultraviolet photoelectron spectrum of Example 1.
[0018] Figure 4 The spectral response, responsivity, specific detectivity, and IV curves at different wavelengths of the device in Example 1 are shown.
[0019] Figure 5 The image shows the intensity-dependent IV vs. It curves for the device at 560 nm and 660 nm light intensity of Example 1.
[0020] Figure 6 The response speed and stability of the device in Example 1 are shown. Detailed Implementation
[0021] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the following embodiments are for illustrative purposes only and are not intended to limit the scope of protection of this invention.
[0022] This invention selects a first perovskite material and a second perovskite material to construct a heterojunction based on the principle of lattice matching. The two materials should have the same or similar crystal structures and close lattice constants. Their lattice constants are determined by X-ray diffraction, and the lattice mismatch is calculated using the formula:
[0023]
[0024] In the formula: a sub and a epi These are the lattice constants of the corresponding crystal planes of the substrate and the epitaxial layer, respectively.
[0025] When the mismatch is less than 5%, coherent or semi-coherent interfaces are easily formed, and less than 3% is even better. In a preferred embodiment of the present invention, the first perovskite material is MAPbBr3 (lattice constant). The second perovskite material is MAPbI3 (lattice constant). The mismatch is approximately 2.0%, which meets the requirements for high-quality epitaxy.
[0026] Example 1
[0027] In this embodiment, cubic perovskite material MAPbBr3 is selected as the first perovskite (wide bandgap) and MAPbI3 is selected as the second perovskite (narrow bandgap). The simplified preparation process is as follows:
[0028] First, a MAPbBr3 single-crystal substrate was prepared using a spatial confinement method. Then, a MAPbI3 epitaxial layer was grown on the substrate using liquid-phase epitaxy. Finally, an Au electrode was deposited via thermal evaporation to obtain a detector with an ITO / MAPbBr3 / MAPbI3 / Au structure, as shown below. Figure 1 .
[0029] Band structure determination:
[0030] The band structure parameters of the two materials were determined using ultraviolet-visible absorption spectroscopy and ultraviolet photoelectron spectroscopy, such as... Figure 2-3 MAPbBr3: Secondary electron cutoff edge E cutoff =16.16eV, starting edge of valence band E onset =1.05 eV, combined with the He I light source energy of 21.22 eV, the Fermi level EF is calculated to be -5.06 eV, and the valence band peak E VBM= -6.11 eV. The optical band gap E is obtained by fitting the absorption spectrum Tauc. g =2.22eV, conduction band bottom E CBM = -3.89 eV. MAPbI3: E cutoff =16.67eV, E onset =0.85eV, therefore E F = -4.55eV, E VBM = -5.40eV, E g =1.52eV, E CBM = -3.88eV.
[0031] Based on the above data, a band structure diagram of the heterojunction was constructed, showing that the conduction band bottoms of the two materials are almost aligned (ΔE). C =0.01eV), with a valence band top difference of 0.71eV, forming a typical Type-II band arrangement. A built-in electric field is formed at the interface, pointing from MAPbI3 to MAPbBr3, providing power for self-driven carrier separation. TRPL tests show that the average carrier lifetime of the heterojunction (43.42ns) is significantly shorter than that of pure MAPbBr3 single crystal (64.52ns), confirming the efficient photogenerated carrier transfer at the interface.
[0032] Photoelectric performance testing:
[0033] The normalized spectral response of the device was measured at zero bias, such as Figure 4 (a) The results show that the device exhibits a flat bandpass response in the 540-800 nm band, with a steep short-wavelength cutoff edge and a long-wavelength cutoff edge located near 800 nm, consistent with the intrinsic absorption edge of MAPbI3. The response in the short-wavelength region (<540 nm) is completely suppressed, proving that the MAPbBr3 substrate effectively filters out short-wavelength photons through the CCN mechanism. This filterless bandpass response characteristic stems from the synergistic effect of the intrinsic absorption of the two materials and the CCN mechanism.
[0034] At zero bias, the device achieves a peak responsivity of 6 mA / W at 780 nm, corresponding to a specific detectivity of 3 × 10⁻⁶. 9 Jones meets the requirements for low-light detection, such as Figure 4 (b) and (c). The device exhibits significantly different responses to different wavelengths of light. 560nm and 660nm light (within the bandpass) generate significant photocurrents, while the response to 850nm light (outside the bandpass) almost coincides with the dark current, such as... Figure 4 (d)
[0035] And in Figure 4As shown in (a), a characteristic fluctuation appears in the spectral response curve near 650 nm. This is due to the inherent emission peak of the halogen tungsten lamp used in the test at this wavelength, resulting in a local enhancement of the incident light power. The device generates a real-time, matched photocurrent response to this power change, which precisely demonstrates its transient sensitivity and accurate tracking capability to optical signals. Subsequent calculations of the responsivity and specific detectivity reveal that the local dip at this location reflects the typical sublinear response behavior of the device under weak light conditions, further verifying its stable and discernible photoelectric conversion capability even under nanowatt-level weak light excitation.
[0036] Using monochromatic light at 560nm and 660nm, gradually decreasing from higher to extremely low intensities, the IV and It responses of the device were tested, such as... Figure 5 The results show that even with an incident light power density as low as 0.53 μW / cm², 2 The device can still generate a clearly distinguishable photocurrent signal with a photocurrent amplitude of several hundred picoamperes, significantly higher than the dark current noise (<10). -10 A). The photocurrent increases linearly with increasing light intensity, exhibiting excellent low-light linear response characteristics. This nanowatt-level low-light detection capability is attributed to the low defect density of the lattice-matched heterojunction and the efficient carrier separation of the Type-II band.
[0037] The device's IV curve does not pass through the origin near zero bias, exhibiting photovoltaic (PV) characteristics. Under zero bias, the photocurrent is significantly higher than the dark current, demonstrating that the built-in electric field effectively separates photogenerated carriers, achieving energy-free self-driven detection. Under 560nm and 660nm illumination, the open-circuit voltage is approximately 0.8V, and the short-circuit current increases with increasing light intensity, further confirming the PV working mechanism.
[0038] The transient photocurrent response of the device was tested under pulsed light excitation, such as Figure 6 (a) The rise time required to rise from 10% to 90% of the peak value is 557 ms, and the fall time required to fall from 90% to 10% is 754 ms. The response speed is slower than that of thin film devices, which is a physical manifestation of the longer carrier transit time in thick film single crystal devices, but it still meets the requirements of steady-state optical detection and low-frequency imaging applications.
[0039] The device underwent continuous periodic optical switching testing for 3 hours, such as... Figure 6 (b) The results show that the photocurrent remains highly stable over 3 hours with a decay of less than 2%, the dark current baseline shows no drift, and the waveform maintains a perfect rectangular characteristic. This excellent long-term stability is due to the elimination of grain boundary ion migration channels by the all-single-crystal structure, and the lattice-matched heterojunction suppressing performance degradation under the influence of an electric field.
[0040] The above description is merely a specific embodiment of this application, enabling those skilled in the art to understand or implement this application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of this application. This application is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features claimed herein.
Claims
1. A perovskite bandpass photodetector for weak light detection, characterized in that, include: Transparent conductive substrate; A first perovskite single crystal substrate layer is formed on the transparent conductive substrate, wherein the first perovskite material has a first band gap and a first lattice constant; A second perovskite single crystal epitaxial layer is formed on the first perovskite single crystal substrate layer. The second perovskite material has a second band gap and a second lattice constant, and the second band gap is smaller than the first band gap. The back electrode is formed on the second perovskite single crystal epitaxial layer.
2. The perovskite bandpass photodetector according to claim 1, characterized in that, The conduction band bottom energy level difference ΔE between the first perovskite material and the second perovskite material C ≤0.05eV, valence band top energy level difference ΔE V ≥0.5eV.
3. The low-light self-driven bandpass photodetector according to claim 1, characterized in that, The lattice mismatch between the first perovskite material and the second perovskite material is 1.5% to 2.5%.
4. The perovskite bandpass photodetector according to claim 1, characterized in that, The thickness of the first perovskite single crystal substrate is configured to be sufficient to cause photogenerated carriers generated by short-wavelength photons on the substrate surface to recombine and quench before reaching the heterojunction interface, and the thickness of the second perovskite single crystal epitaxial layer is configured to fully absorb target wavelength photons with energy between the first bandgap and the second bandgap.
5. The perovskite bandpass photodetector according to claim 1, characterized in that, The detector achieves a bandpass response at zero bias to wavelengths between the first and second band gaps.
6. The perovskite bandpass photodetector according to claim 1, characterized in that, The peak responsivity of the bandpass response is ≥5 mA / W, and the specific detectivity is ≥3×10⁻⁶. 9 Jones.
7. The perovskite bandpass photodetector according to claim 1, characterized in that, The detector operates at a power density ≤1μW / cm² under zero bias. 2 The incident light produces a resolvable photocurrent response.
8. The perovskite bandpass photodetector according to claim 1, characterized in that, The defect density at the heterojunction interface was measured to be 9.88 × 10⁻⁶ using the space charge-confined current method. 12 cm -3 .
9. The perovskite bandpass photodetector according to claim 1, characterized in that, The detector exhibits a photocurrent attenuation of less than 2% under continuous 3-hour periodic illumination.
10. An application of a perovskite bandpass photodetector as described in any one of claims 1 to 9 in multispectral imaging, biofluorescence detection, deep-sea optical communication, or Internet of Things sensing.