Photodetectors based on two-dimensional quantum dots

Abstract

A photodetector (200) includes: a bottom electrode (210); an intermediate layer (220) arranged on the bottom electrode; a light absorbing layer (230) arranged on the intermediate layer, the light absorbing layer having one or more charge transport materials and a plurality of two-dimensional quantum dots (2D QDs) dispersed in the one or more charge transport materials; and a top electrode (240) arranged on the light absorbing layer. A heterostructure photodetector (300) includes: a bottom electrode (310); a first light absorbing layer (320) arranged on the first electrode, the first light absorbing layer having a first light absorbing material; a second light absorbing layer (330) arranged on the first light absorbing layer, the second light absorbing layer having a second light absorbing material; and a top electrode (340) arranged on the second light absorbing layer, at least one of the first or second light absorbing materials being a plurality of two-dimensional quantum dots (2D QDs).

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims the benefit of U.S. Provisional Application No. 62 / 722,006, filed on August 23, 2018, the entire contents of which are incorporated herein by reference. Background of the Invention

[0003] 1. Field of the Invention

[0004] The present invention generally relates to semiconductor nanoparticles, commonly referred to as "quantum dots" (QDs). More particularly, the present invention relates to quantum dots comprising two-dimensional materials and their use in photodetectors.

[0005] 2. Description of the related art including information disclosed pursuant to 37 CFR 1.97 and 1.98.

[0006] A photodetector is a device that generates an electrical signal in response to incident photons. A photodetector or light sensor responds to the intensity of light or other electromagnetic energy incident on it. A solid-state photodetector has a pn junction that converts photons of light into an electric current. The absorbed photons form electron-hole pairs in the depletion region. Photodiodes, photoconductors, and phototransistors are examples of photodetectors. In a sense, solar cells are photodetectors because they convert some of the light energy they absorb into electrical energy, the amount of which can be sensed by appropriate circuitry.

[0007] Photodiodes are typically based on pn junctions. In a photodiode, when photons of sufficient energy strike the device, electron-hole pairs are formed. If absorption occurs in the depletion region of the junction or a diffusion length away from it, the built-in electric field of the depletion region causes carriers to be swept out of the junction, with holes moving toward the anode and electrons moving toward the cathode, thereby generating a photocurrent.

[0008] A photoconductor is a device that detects temporary changes in the conductivity of a semiconductor caused by the illumination of light. The photons generate photoexcited carriers that are extracted by the electric field generated by a bias voltage applied between electrodes.

[0009] A phototransistor is similar to a photodiode, with the addition of another n-type region. A phototransistor comprises a photodiode with internal gain. It can be represented as a bipolar transistor enclosed in a transparent housing so that photons can reach the base-collector junction. Electrons generated by photons in the base-collector junction are injected into the base, thereby amplifying the current.

[0010] Each of these three types of photodetectors has different characteristics and therefore can be used in different applications. Phototransistors and photodiodes detect at similar rates, but phototransistors have a slower response time (microseconds, compared to nanoseconds for photodiodes). Phototransistors have higher gain, while photodiodes have smaller temperature changes.

[0011] Photodetectors can be used in different configurations. A single sensor can detect the overall light level. A 1-D array of photodetectors can be used to measure the distribution of light along a line, as in a spectrophotometer or line scanner. A 2-D array of photodetectors can be used as an image sensor to form an image from the pattern of light incident on it.

[0012] The photodetector or array is typically covered by an illumination window, which may have an anti-reflective coating.

[0013] There are many performance metrics (so called "worthwhile numbers") that can be used to characterize or compare photodetectors. One performance metric is the spectral response (the response of the photodetector as a function of photon frequency). Another performance metric is the quantum efficiency (QE; the number of carriers (electrons or holes) generated per photon). Yet another performance metric is the responsivity (R; the output current divided by the total optical power falling on the photodetector. R = QE / E). 光子 , where E 光子 is the photon energy in eV). Yet another performance indicator is the noise equivalent power (NEP; minimum detectable power, i.e., the optical signal at which the electrical noise ratio in the detector is equal to one (0 dB) when the bandwidth is limited to 1 Hz). Yet another performance indicator is the specific detectivity (D*; detector area A multiplied by the square root of the frequency bandwidth B divided by the noise equivalent power; D* = [√(AB)] / NEP). Yet another performance indicator is the gain (G; the output current of the photodetector divided by the current directly generated by the photons incident on the detector, i.e., the built-in current gain). Yet another performance indicator is the dark current (I d ; the current that flows through the photodetector even in the absence of light). Yet another performance metric is the response time (τ; the time it takes the photodetector to go from 10% to 90% of its final output). Yet another performance metric is the noise spectrum (the inherent noise voltage or current that varies with frequency; this can be expressed in terms of noise spectral density). Yet another performance metric is nonlinearity (the RF output is limited by the nonlinearity of the photodetector). Yet another performance metric is spectral selectivity (the cutoff wavelength beyond which the response signal is comparable to or less than the noise level).

[0014] To achieve high performance of photodetectors, a combination of high responsivity, short response time, high specific density, and a wide spectrally selective wavelength range is desirable.

[0015] There is growing interest in solution-processable photodetectors with sensitivity spanning the ultraviolet (UV) to near-infrared (NIR) range for applications such as imaging sensors. Of particular interest is the 1-1.8 μm range, where water absorption is low.

[0016] The potential use of colloidal quantum dots (QDs) as light absorbers in photodetection applications has been recognized, with research mainly focused on PbS QDs containing toxic lead.

[0017] Due to their combination of optical properties and mechanical flexibility, 2D materials, including graphene and transition metal dichalcogenides (TMDCs), have been studied as light absorbers for photodetection applications. Graphene-based photodetectors have been extensively studied and have been shown to exhibit high carrier mobility, excellent stability, high mechanical strength, and a spectral response spanning the visible to far infrared. However, difficulties in opening the band gap of graphene result in high dark currents, limiting their applicability for photodetection. Layered TMDCs offer many advantages, including band gaps that can be tuned by the number of layers. They are also compatible with complementary metal-oxide-semiconductor (CMOS) technology, which can be used to build integrated circuits, enabling the development of versatile, high-performance photodetectors with low power consumption.

[0018] Due to its narrow thickness (which limits light absorption), it is currently difficult to produce photodetectors with high responsivity, broadband spectrum and high detectivity using a single TMDC. Using highly absorptive sensitizers can help improve light absorption efficiency, but the sensitizer needs to be thin enough to retain the advantages of 2D materials. For efficient charge separation and transfer, high carrier mobility and a band structure that is well matched to the TMDC are also desirable.

[0019] Colloidal QDs have been used as sensitizers in combination with TMDC sheets to achieve sensitive, fast, and broadband photodetectors. For example, PbS QDs have been used in combination with WSe2 nanosheets [C. Hu et al., Adv. Funct. Mater. 2017, 27, 1603605], and CdS / ZnS QDs have been combined with WS2 monolayers [A. Baulesbaa, K. Wang, M. Mahjouri-Somani, M. Tian, ​​AAPuretzky, I. Ivanov, CMRouleau, K. Xiao, BG Sumpter and DB Grohegan, J. Am. Chem. Soc., 2016, 138, 14713].

[0020] Compared to QDs, nanosheets have a larger contact area, so hybrid devices with 2D nanosheets of materials such as graphene and other layered materials together with TMDCs have been studied. For devices with 2D heterostructures as sensitizers, the formation of Schottky barriers at the heterostructure interface can lead to an intrinsic electric field, thereby providing efficient charge transfer at the interface.

[0021] Therefore, both colloidal QDs and 2D nanosheets may offer advantages for photodetector applications.

[0022] Traditionally, crystalline silicon has been used for photodetection applications. However, its absorption is limited to below 1.1 μm, which means that it cannot absorb most of the infrared (IR) spectrum. In addition, its absorption is weak across its spectrum, exceeding only 104 cm at 500 nm. -1 In the ultraviolet region, at wavelengths relevant for detecting skin cancer, ultrashort absorption wavelengths in silicon lead to the creation of electron-hole pairs near highly recombined surface states. This limits the UV sensitivity in standard silicon devices. Therefore, there is great interest in materials that can absorb light beyond the range of silicon.

[0023] Epitaxially grown QDs have been used for photodetection applications, but can be difficult to process. All-organic semiconductors could offer convenient processing for photodetection applications. However, until recently, there were few available small organic molecules or polymers with narrow band gaps suitable for making photodiodes in the near-infrared range.

[0024] QD photodiode devices can be tuned into the near-infrared range beyond the spectral range of organic semiconductors, but a major problem lies in the reliance on QDs based on toxic heavy metals such as lead or cadmium.

[0025] Photodetectors incorporating light absorbers based on 2D materials such as graphene and TMDCs have been explored. Advantages include their unique optical properties and mechanical flexibility. Other desirable properties include high carrier mobility, chemical stability, mechanical strength, and spectral response that can be tuned from the visible region to the far infrared region. In particular, TMDC-based photodetectors can be tuned by varying the number of layers. Heterostructures of two different layered materials have also been explored. Weak van der Waals interactions between two advantageously arranged materials can generate high-quality heterojunctions without problems caused by lattice mismatch between the two materials.

[0026] Heterostructure devices including CdSe-based 2D nanoplates and graphene have been described. [A. Robin, E. Lhuillier and B. Dubertret, MRS Adv., 2016, 2187; A. Robin, E. Lhuillier, XZ Xu, S. Ithurria, H. Aubin, A. Ouerghi and B. Dubertret, Sci. Rep., 2016, 6, 24909]. The device takes advantage of the strong absorptivity of the nanoplates and the high carrier mobility of graphene. The thickness of the 2D nanoplates is 1-5 nm, and the lateral dimensions are up to 1 μm, making the lateral dimensions much larger than the Bohr radius. The disadvantage of these nanoplates is that they cannot provide bandgap adjustability.

[0027] For photodetectors that incorporate layers of 2D materials, one issue that must be addressed is the elimination of deep trap states that are detrimental to response speed.

[0028] Although many photodetector devices integrating 2D materials have been reported, existing technologies rely on peel-off or CVD deposition processes that are difficult to scale. SUMMARY OF THE INVENTION

[0030] Photodetectors according to aspects of the present disclosure may include a plurality of semiconductor nanoparticles having lateral dimensions within a quantum confinement regime and a thickness of 1 to 5 atomic or molecular monolayers, inclusive ("2D quantum dots" or "2D QDs").

[0031] Some advantages of using QDs in photodetector applications include strong, tunable absorption spectra and solution processability. Some advantages of using 2D materials include high contact area and surface flatness, tunability of absorption via material thickness, high mobility and high transparency.

[0032] By using 2D QDs instead of other conventional forms of QDs (i.e., 0D spherical QDs, 1D QDs (e.g., nanorods), or 3D QDs (e.g., nanocubes, nanopyramids, nanocones, etc.)) and / or 2D layered materials, the combined advantages of QDs and 2D materials can be achieved. Additional absorption tunability can be achieved by modifying the QD thickness, and 2D QDs can be composed of non-toxic materials, thereby alleviating concerns about the toxicity of QDs based on heavy metals such as cadmium and lead.

[0033] Solution-processable photodetectors are of particular benefit in sensor applications.

[0034] In a first aspect of the present invention, a photodetector is provided, comprising: a first electrode; an interlayer arranged on the first electrode; a light absorbing layer arranged on the interlayer, the light absorbing layer comprising: one or more charge transport materials; and a plurality of two-dimensional quantum dots (2D QDs) dispersed in the one or more charge transport materials; and a second electrode arranged on the light absorbing layer.

[0035] The thickness of the intermediate layer can be in the range of about 1 nm to about 1000 nm. The light absorbing layer can include about 10 volume % to about 95 volume % of 2D QDs. The light absorbing layer can include about 5 volume % to about 90 volume % of one or more charge transport materials. The thickness of the light absorbing layer can be in the range of about 10 nm to about 2 microns. The 2D QD can have a thickness of about 1 to about 5 atomic or molecular monolayers and a lateral size sufficient to keep the 2D QD within the quantum confinement range.

[0036] In a second aspect of the present invention, a heterostructure photodetector is provided, which includes: a first electrode; a first light absorption layer arranged on the first electrode, the first light absorption layer including a first light absorption material; a second light absorption layer arranged on the first light absorption layer, the second light absorption layer including a second light absorption material; and a second electrode arranged on the second light absorption layer.

[0037] The heterostructure photodetector may further include an intermediate layer arranged between the first electrode and the first light absorbing layer. The heterostructure photodetector may further include a transition layer arranged between the first light absorbing layer and the second light absorbing layer, the transition layer including a combination of a first light absorbing material and a second light absorbing material. The first light absorbing material may be a plurality of two-dimensional quantum dots (2D QDs), a plurality of two-dimensional nanosheets (2D nanosheets), or a plurality of conventional QDs. The first light absorbing material may be a plurality of two-dimensional quantum dots (2D QDs). The first light absorbing material may be a plurality of two-dimensional nanosheets (2D nanosheets). The first light absorbing material may be a plurality of conventional QDs. The second light absorbing material may be a plurality of 2D QDs, a plurality of 2D nanosheets, or a plurality of conventional QDs. The second light absorbing material may be a plurality of 2D QDs. The second light absorbing material may be a plurality of 2D nanosheets. The second light absorbing material may be a plurality of conventional QDs. In an embodiment, the first light absorbing material is a plurality of 2D nanosheets and the second light absorbing material is a plurality of 2DQDs. In an embodiment, the first light absorbing material is a plurality of first 2D QDs and the second light absorbing material is a plurality of second 2DQDs. In an embodiment, the first light absorbing material is a plurality of 2D QDs and the second light absorbing material is a plurality of conventional QDs. It is possible that the first light absorbing material is a plurality of conventional QDs and the second light absorbing material is a plurality of 2D QDs. It is possible that the first light absorbing material is a plurality of 2D QDs and the second light absorbing material is a plurality of 2D nanosheets. The valence band and conduction band of the first light absorbing material may deviate from the valence band and conduction band of the second light absorbing material to generate a built-in electric field. The combined thickness of the first light absorbing layer and the second light absorbing layer may be in the range of about 50nm to about 800nm. It is possible that one of the first light absorbing layer and the second light absorbing layer further includes a charge transport material. It is possible that one of the first light absorbing material and the second light absorbing material is a plurality of 2D nanosheets having a thickness of 1 to 10 atomic or molecular monolayers and a lateral dimension extending beyond the quantum confinement range. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 Shown are the chemical structures of various charge transport polymers that can be combined with 2D QDs to produce 2D QD-sensitized organic photodiodes according to aspects of the present disclosure.

[0040] Figure 2 is a schematic diagram of a photodetector device including 2D QDs within an organic photodiode according to aspects of the present disclosure.

[0041] Figure 3 is a schematic diagram of a heterostructure photodetector including a first layer of 2D QDs and a second layer of 2D nanosheets according to aspects of the present disclosure.

[0042] Figure 4 is a schematic diagram of a heterostructure photodiode according to aspects of the present disclosure, the heterostructure photodiode comprising a first layer of 2D QDs and a second layer of 2D QDs.

[0043] Figure 5 is a schematic diagram of a heterostructure photodetector including a first layer of conventional QDs and a second layer of 2D QDs according to aspects of the present disclosure.

[0044] Figure 6 is a schematic diagram of a heterostructure photodetector including a first layer of 2D QDs and a second layer of conventional QDs according to aspects of the present disclosure.

[0045] Figure 7 is a schematic diagram of a heterostructure photodetector including a first layer of 2D nanosheets and a second layer of 2D QDs according to aspects of the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0047] The following description of the embodiments is merely exemplary in nature and is in no way intended to limit the subject matter of the present disclosure, its application, or uses.

[0048] As used throughout, ranges are used as shorthand for describing each value within the range. Any value within the range can be selected as the endpoint of the range. Unless otherwise indicated, all percentages and amounts expressed herein and elsewhere in the specification are understood to refer to weight percentages.

[0049] For the purpose of this specification and the appended claims, unless otherwise indicated, all numbers used in the specification and the claims indicating quantities, percentages or ratios and other numerical values ​​should be understood to be modified by the term "about" in all cases. The use of the term "about" applies to all numerical values, whether or not explicitly stated. The term generally refers to a numerical range that a person of ordinary skill in the art would consider to have a reasonable deviation amount (i.e., having an equivalent effect or result) from the stated numerical value. For example, the term can be interpreted as including deviations of ±10%, alternatively ±5%, and alternatively ±1% of a given numerical value, provided that such deviations do not change the ultimate effect or result of the value. Therefore, unless otherwise indicated, the numerical parameters set forth in this specification and the appended claims are approximate values ​​that may vary depending on the ideal properties attempted to be obtained by the present invention.

[0050] It should be noted that, as used in this specification and the appended claims, the singular forms "a", "an", and "the" include plural references unless clearly and unambiguously limited to one referent. As used herein, the term "include" and its grammatical variants are intended to be non-restrictive, so that the recitation of items in a list does not exclude other similar items that can be replaced or added to the listed items. For example, as used in this specification and the following claims, the terms "comprise" (and its forms, derivatives, or variants, such as "comprising" and "comprises"), "include" (and its forms, derivatives, or variants, such as "including" and "includes") and "have" (and its forms, derivatives, or variants, such as "having" and "have") are inclusive (i.e., open-ended) and do not exclude additional elements or steps. Therefore, these terms are intended to cover not only the one or more elements or steps that are recorded, but also other elements or steps that are not explicitly recorded. Furthermore, as used herein, the use of the terms “a” or “an” when used in conjunction with an element may mean “one”, but it is also consistent with the meaning of “one or more”, “at least one” and “one or more than one”. Therefore, without more limitations, an element preceded by “a” or “an” does not preclude the presence of additional identical elements.

[0051] For more than 20 years, the study of the properties of colloidal QDs and their optoelectronic devices has been of great interest. Recently, people have become increasingly interested in the unique properties of two-dimensional quantum dots (2D QDs). As used herein, "2D quantum dots" or "2D QDs" refer to semiconductor nanoparticles with a thickness of about 1-5 atomic or molecular monolayers and a lateral dimension that causes nanoparticles to be within the quantum confinement range-that is, the electronic properties of the nanoparticles are different from the electronic properties of the bulk material. As can be understood, the lateral dimensions that provide electronic properties indicating the quantum confinement range for nanoparticles can vary between nanoparticles with different compositions. However, such lateral dimensions can generally be 1 to 100 nm. As used herein, the term "2D nanosheet" is used to describe particles with a thickness of 1 to 10 atomic or molecular monolayers, and wherein the lateral dimensions are large enough that they extend beyond the quantum confinement range. As used herein, "monolayer quantum dots" or "monolayer QDs" refer to semiconductor nanoparticles with a thickness of a single monolayer and a lateral dimension that causes nanoparticles to be within the quantum confinement range. Compared with conventional zero-dimensional (0D) QDs, 2D QDs have a much higher surface area to volume ratio, which increases as the number of monolayers decreases. The highest surface area to volume ratio is observed for monolayer QDs. This can lead to 2D QDs with surface chemistry that is very different from conventional QDs, which can be used in many applications. To date, most studies on 2D QDs have focused on layered materials, such as carbon-based materials (e.g., graphene and graphene oxide) and TMDC (especially MoS2, MoSe2, WS2 and WSe2) QDs. However, recently, people have been interested in the synthesis of 2D nanoparticles of conventional semiconductor materials such as II-VI (group) semiconductors [E. Lhuillier et al., Acc. Chem. Res., 2015, 48, 22; A. Riedinger et al., Nat. Mater., 2017, 16, 743].

[0052] In some embodiments, the photodetector is a photodiode. Photodiodes are typically based on pn junctions. In a photodiode, when photons of sufficient energy strike the device, electron-hole pairs are formed. If absorption occurs in the depletion region of the junction or a diffusion length away from it, the built-in electric field of the depletion region causes carriers to be swept out of the junction, with holes moving toward the anode and electrons moving toward the cathode, thereby generating a photocurrent.

[0053] In some embodiments, the photodetector is a photoconductor. A photoconductor is a device that detects temporary changes in the conductivity of a semiconductor produced by light irradiation. Photons generate photoexcited carriers that are extracted by the electric field generated by a bias voltage applied between the anode and cathode electrodes of the photodetector.

[0054] In some embodiments, the photodetector is a phototransistor with a base-collector junction. A phototransistor is similar to a photodiode, with an additional n-type region added. A phototransistor includes a photodiode with internal gain. It can be represented as a bipolar transistor enclosed in a transparent housing so that photons can reach the base-collector junction. Electrons generated by photons in the base-collector junction are injected into the base, thereby amplifying the current.

[0055] Each of these three types of photodetectors has different properties and can therefore be used in different applications. Phototransistors and photodiodes have similar detection rates, but phototransistors have slower response times (microseconds, compared to nanoseconds for photodiodes). Phototransistors have higher gain, while photodiodes exhibit smaller temperature changes.

[0056] In at least one embodiment, a 2D QD-sensitized organic photodiode is used. In at least one embodiment, a heterostructure photodetector comprising a 2D QD and a 2D nanosheet layer (i.e., having lateral dimensions well beyond the quantum confinement range) is used. In at least one embodiment, a heterostructure photodetector comprising a first 2D QD layer and a second layer of 2D QDs of other materials is used. In at least one embodiment, a heterostructure photodetector comprising a conventional QD layer and a 2D QD layer is used.

[0057] Figure 2 is a schematic diagram of a photodetector 200 according to aspects of the present disclosure. The photodetector 200 includes a bottom electrode 210, an intermediate layer 220 disposed on the bottom electrode 210, a layer 230 including 2D QDs dispersed in a charge transport material disposed on the intermediate layer 220, and a top electrode 240 disposed on the layer 230 containing 2D QDs. Figure 2 In the device configuration shown, one or more of the top and bottom electrodes 210, 240 can be transparent to allow light to pass therethrough. The bottom electrode 210 can include a transparent conductive oxide, such as indium tin oxide (ITO) and aluminum-doped zinc oxide (AZO). The top electrode 240 can include one or more low work function metals, such as aluminum and silver.

[0058] The intermediate layer 220 is used to improve the electrical contact with the bottom electrode 210 below. The intermediate layer 220 can be made of any suitable material, such as, for example, poly (3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS), MoO3, and metal oxides with zinc, titanium, vanadium or nickel. The thickness of the intermediate layer 220 can be in the range of about 1 nm to about 1000 nm, alternatively about 10 nm to about 1000 nm, and alternatively about 100 nm to about 1000 nm.

[0059] exist Figure 2 As schematically shown in , a layer 230 comprising 2D QDs dispersed in a charge transport material can be produced by dispersing (by blending or mixing) 2D QDs in one or more organic charge transport materials (electron and / or hole accepting and transporting organic materials) to form a heterojunction. Examples of suitable charge transport materials include, but are not limited to: [6,6]-phenyl-C61-butyric acid methyl ester (PCBM), poly (3-hexylthiophene) (P3HT), poly (N-octyldithieno [3,2-b:2'3'd] pyrrole-alternate (alt) -5,6-bis (octyloxy) benzo [c] [1,2,5] thiadiazole) (PDTPBT), poly [(9,9-dioctylfluorenyl-2,7-diyl-co (4,40-(N-4-sec- butylphenyl))diphenylamine)] (TFB), poly (N,N'-bis (4-butylphenyl)-N,N'-bis (phenyl)-benzidine) (poly-TPD), poly (2-methoxy-5 (2'-ethylhexyloxy)-1,4-phenylethylene vinylene) (MEH-PPV), poly (2,5-bis (2'-ethylhexyloxy)-1,4-phenylethylene vinylene) (DEH-PPV), poly [2,6-(4,4'-bis (2-ethylhexyl) dithieno[3,2-b:2',3'-d]silole-alt-4,7(2,1,3-benzothiadiazole) (PSBTBT), poly[2,6-(4,4-bis(2-ethylhexyl)4H-cyclopenta[2,1-b;3,4-b']dithiophene)-alt-4,7-(2,1,3-benzothiadiazole)] (PCPDTBT), poly(2,3-didecyl-quinoxaline-5,8-diyl-alt-N-octyldithieno[3,2 -b:2'3'-d]pyrrole)(PDTPQx), dithieno[3,2-b:2,3-d]pyrrole (DTP), poly(9,9-n-dihexyl-2,7-fluorenylidenevinylene-alternative-2,5-thienylenevinylene) (PFT), ethoxylated polyethyleneimine (PEIE), 1-1-bis[(di-4-methylphenylaminophenyl]cyclohexane (TAPC), C60, multi-walled carbon nanotubes and other polymers, some of which have structures in Figure 1 In Figure 1 The number average molar mass M of PDTPBT is n It can be found at about 17 kg mol -1 to about 19 kgmol -1 In addition, Figure 1 In the PDBF, M n It can be found in about 11 kg mol -1 About 13 kg mol -1 In addition, Figure 1 In the PDTD, M nIt can be used at about 30 kg mol -1 About 35 kg mol -1 In addition, Figure 1 In the PDTT, M n It can be used at about 30 kg mol -1 About 35 kg mol -1 In addition, Figure 1 In PDFT, M n It can be about 35kgmol -1 About 40 kg mol -1 In addition, Figure 1 In the PBDTTPD n It can be found in about 10 kg mol -1 to about 35 kgmol -1 In addition, Figure 1 In the experiment, the M of PBDT-T8-TPD n It can be found in about 35 kg mol -1 About 40 kg mol -1 In addition, Figure 1 In the case of P3HT, M n It can be used at about 50 kg mol -1 About 80 kg mol -1 Finally, in Figure 1 In the PBDT-T-FDP, M n It can be used at about 50 kg mol -1 About 60 kg mol -1 within the range.

[0060] Another material suitable for use as an organic material in a 2D-sensitized organic photodiode is spiro-OMeTAD, which can provide both UV detection and hole transport properties (see Guo et al., J Mater. Chem. C, 2018, 6, 2573). As discussed above, an intermediate layer, such as but not limited to poly (3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS), can be used to improve the electrical connection to the bottom contact. Alternative suitable materials may include solution-processable MoO3 or V2O x to replace PEDOT.

[0061] In some cases, the layer 230 containing 2D QDs includes about 10 volume % to about 95 volume % of 2D QDs and about 5 volume % to about 90 volume % of one or more charge transport materials. In some cases, the layer 230 containing 2D QDs includes about 20 volume % to about 90 volume %, alternatively about 30 volume % to about 85 volume %, alternatively about 40 volume % to about 80 volume %, alternatively about 50 volume % to about 75 volume % and alternatively about 60 volume % to about 70 volume % of 2D QDs. In some cases, the layer 230 containing 2D QDs includes about 10 volume % to about 80 volume %, alternatively about 15 volume % to about 70 volume %, alternatively about 20 volume % to about 60 volume %, alternatively about 25 volume % to about 50 volume % and alternatively about 30 volume % to about 40 volume % of one or more charge transport materials.

[0062] The thickness of the 2D QD-containing layer 230 may be in a range from about 10 nm to about 2 micrometers, alternatively from about 50 nm to about 1 micrometer, and alternatively from about 100 nm to about 750 nm, and alternatively from about 200 nm to about 500 nm.

[0063] Figure 3 is a schematic diagram of a heterostructure photodetector 300 according to aspects of the present disclosure. The heterostructure photodetector 300 includes a bottom electrode 310, and a first layer 320 having 2D nanosheets disposed on the bottom electrode 310, a second layer 330 having 2D QDs disposed on the first layer 320 containing the 2D nanosheets, and a top electrode 340 disposed on the second layer 330 containing the 2D QDs. In this configuration, one or more of the top and bottom electrodes 310, 340 may be transparent to allow light to pass therethrough. To form a heterojunction, the 2D QDs and 2D nanosheets in the layers 320, 330 are selected so that the conduction band and valence band of the 2D QDs deviate from the conduction band and valence band of the 2D nanosheets to form a built-in electric field. This can be achieved by selecting 2D QD and 2D nanosheet materials with different semiconductor bandgaps, and / or adjusting the lateral size of the second 2D QD and / or 2D nanosheet, and / or adjusting the thickness of the 2D QD and / or 2D nanosheet, and / or functionalizing the surface of one or both of the 2D QD and 2D nanosheet with different ligands that change the bandgaps of the materials. The junction width can control the wavelength of light absorbed.

[0064] The thickness of each of the layer 320 containing 2D nanosheets and the layer 330 containing 2D QDs can be independently in the range of about 10 nm to about 1 micron, alternatively about 25 nm to about 750 nm, alternatively about 50 nm to about 500 nm, alternatively about 75 nm to about 400 nm, and alternatively about 100 nm to about 300 nm. Preferably, the combined thickness of the layer 320 containing 2D nanosheets and the layer 330 containing 2D QDs is about 50 nm to about 800 nm, more preferably about 100 nm to about 700 nm, and even more preferably about 200 nm to about 600 nm. In some cases, the layer 320 containing 2D nanosheets and the layer 330 containing 2D QDs have the same or substantially the same thickness. In other cases, the layer 330 containing 2D QDs is thicker than the layer 320 containing 2D nanosheets. In other cases, the layer 320 containing 2D nanosheets is thicker than the layer 330 containing 2D QDs.

[0065] The layer 330 containing 2D QDs can be prepared to have the same or substantially similar composition as the layer 230 containing 2D QDs. Like the layer 230 containing 2D QDs, the layer 320 containing 2D nanosheets includes about 10% to about 95% by volume of 2D nanosheets and about 5% to about 90% by volume of one or more charge transport materials. In some cases, the layer 320 containing 2D nanosheets includes about 20% to about 90% by volume, alternatively about 30% to about 85% by volume, alternatively about 40% to about 80% by volume, alternatively about 50% to about 75% by volume, and alternatively about 60% to about 70% by volume of 2D nanosheets. In some cases, layer 320 containing 2D nanosheets includes about 10 vol % to about 80 vol %, alternatively about 15 vol % to about 70 vol %, alternatively about 20 vol % to about 60 vol %, alternatively about 25 vol % to about 50 vol %, and alternatively about 30 vol % to about 40 vol % of one or more charge transport materials.

[0066] In some cases, the heterostructure photodetector 300 may further include an intermediate layer (not shown) disposed between the bottom electrode 310 and the layer 320 containing 2D nanosheets. The intermediate layer may be made of the same material as the intermediate layer 220 of the photodetector 200. Figure 3, a layer 320 containing 2D nanosheets and a layer 330 containing 2D QDs are shown as separate layers. In some cases, a transition layer (not shown) may be disposed between the layer 320 containing 2D nanosheets and the layer 330 containing 2D QDs, the transition layer having a combination of 2D nanosheets and 2D QDs. In some cases, the relative amounts of 2D nanosheets and 2D QDs may be uniform or substantially uniform over the entire thickness of the transition layer. In some cases, the transition layer may exhibit a gradient in which the amount of 2D nanosheets decreases from the layer 320 containing 2D nanosheets to the layer 330 containing 2D QDs. In some cases, the transition layer may exhibit a gradient in which the amount of 2D QDs increases from the layer 320 containing 2D nanosheets to the layer 330 containing 2D QDs.

[0067] Figure 4 is a schematic diagram of another heterostructure photodetector 400 according to aspects of the present disclosure. The heterostructure photodetector 400 includes a bottom electrode 410, and a first layer 420 with 2D QDs disposed on the bottom electrode 410, a second layer 430 with 2D QDs disposed on the first layer 420 containing 2D QDs, and a top electrode 440 disposed on the second layer 430 containing 2D QDs. In this configuration, one or more of the top and bottom electrodes 410, 420 can be transparent to allow light to enter the device. To form a heterojunction, the 2D QDs of the first layer 420 and the 2D QDs of the second layer 430 are selected so that the conduction band and valence band of the 2D QDs in the first layer 420 deviate from the conduction band and valence band of the 2D QDs in the second layer 430. This can be achieved by selecting first and second 2D QDs of materials having different semiconductor bandgaps, and / or adjusting the lateral dimensions of the first and second 2D QDs, and / or adjusting the thickness of the first and second 2D QDs, and / or functionalizing the surface of one or both of the first and second 2D QDs with different ligands that change the bandgaps of the materials. In some cases, the chemical composition of each of the first and second 2D QDs can be the same or substantially the same, but the first and second 2D QDs are different in one or more of the lateral dimensions, thickness, and surface functionalization. The junction width can control the wavelength of light absorbed.

[0068] The composition and / or thickness of each 2D QD-containing layer 420, 430 can vary as described above for the 2D QD-containing layer 230. Preferably, the combined thickness of the 2D QD-containing layers 420, 430 is from about 50 nm to about 800 nm, more preferably from about 100 nm to about 700 nm, and even more preferably from about 200 nm to about 600 nm. In some cases, each 2D QD-containing layer 420, 430 has the same or substantially the same thickness. In other cases, the 2D QD-containing layer 420 is thicker than the 2D QD-containing layer 430. In other cases, the 2D QD-containing layer 430 is thicker than the 2D QD-containing layer 420.

[0069] In some cases, the heterostructure photodetector 400 may further include an intermediate layer (not shown) disposed between the bottom electrode 410 and the layer 420 containing 2DQDs. The intermediate layer may be made of the same material as the intermediate layer 220 of the photodetector 200. Figure 4 , the layer 420 containing 2D QDs and the layer 430 containing 2D QDs are shown as separate layers. In some cases, a transition layer (not shown) can be arranged between the layer 420 containing 2D QDs and the layer 430 containing 2D QDs, the transition layer having a combination of a first 2D QD (i.e., the 2D QDs of layer 420) and a second 2D QD (i.e., the 2D QDs of layer 430). In some cases, the relative amount of the first 2D QD and the second 2D QD can be uniform or substantially uniform throughout the thickness of the transition layer. In some cases, the transition layer can exhibit a gradient, wherein the amount of the first 2D QD decreases from the layer 420 containing 2D QDs to the layer 430 containing 2D QDs. In some cases, the transition layer can exhibit a gradient, wherein the amount of the second 2D QD increases from the layer 420 containing 2D QDs to the layer 430 containing 2D QDs.

[0070] Figure 5is a schematic diagram of yet another heterostructure photodetector 500 according to aspects of the present disclosure. The heterostructure photodetector 500 includes a bottom electrode 510, a first layer 520 having 2D QDs disposed on the bottom electrode 510, and a second layer 530 having conventional QDs disposed on the first layer 520 containing 2D QDs, and a top electrode 540 disposed on the second layer 530 containing conventional QDs. In this configuration, one or more of the top and bottom electrodes 510, 540 may be transparent to allow light to enter the device. To form a heterojunction, the first 2D QD layer 520 and the second conventional QD layer 530 are selected so that the conduction band and valence band of the first 2D QD layer deviate from the conduction band and valence band of the second conventional QD layer. This can be achieved by selecting conventional QDs and 2D QDs of materials with different semiconductor bandgaps, and / or adjusting the diameter of the conventional QDs, and / or adjusting the lateral size of the 2D QDs, and / or adjusting the thickness of the 2D QDs, and / or functionalizing the surface of one or both of the 2D QDs and conventional 2D QDs with different ligands that change the bandgaps of the materials. The junction width can control the wavelength of light absorbed.

[0071] The layer 520 containing 2D QDs can be prepared to have the same or substantially similar composition as the layer 230 containing 2D QDs. Like the layer 230 containing 2D QDs, the layer 520 containing 2D nanosheets includes about 10 volume % to about 95 volume % of 2D nanosheets and about 5 volume % to about 90 volume % of one or more charge transport materials. In some cases, the layer 530 containing conventional QDs includes about 20 volume % to about 90 volume %, alternatively about 30 volume % to about 85 volume %, alternatively about 40 volume % to about 80 volume %, alternatively about 50 volume % to about 75 volume %, and alternatively about 60 volume % to about 70 volume % of conventional QDs. In some cases, layer 530 containing conventional QDs includes about 10 vol % to about 80 vol %, alternatively about 15 vol % to about 70 vol %, alternatively about 20 vol % to about 60 vol %, alternatively about 25 vol % to about 50 vol %, and alternatively about 30 vol % to about 40 vol % of one or more charge transport materials.

[0072] In some cases, the heterostructure photodetector 500 may further include an intermediate layer (not shown) disposed between the bottom electrode 510 and the layer 520 containing 2DQDs. The intermediate layer may be made of the same material as the intermediate layer 220 of the photodetector 200. Figure 5, a layer 520 containing 2D QDs and a layer 530 containing conventional QDs are shown as separate layers. In some cases, a transition layer (not shown) may be disposed between the layer 520 containing 2D QDs and the layer 530 containing conventional QDs, the transition layer having a combination of 2D QDs (i.e., 2D QDs of layer 520) and conventional QDs (i.e., conventional QDs of layer 530). In some cases, the relative amounts of 2D QDs and conventional QDs may be uniform or substantially uniform throughout the thickness of the transition layer. In some cases, the transition layer may exhibit a gradient in which the amount of 2D QDs decreases from the layer 520 containing 2D QDs to the layer 530 containing conventional QDs. In some cases, the transition layer may exhibit a gradient in which the amount of conventional QDs increases from the layer 520 containing 2D QDs to the layer 530 containing conventional QDs.

[0073] Figure 6 6 is a schematic diagram of yet another heterostructure photodetector 600 according to aspects of the present disclosure. The heterostructure photodetector 600 includes a bottom electrode 610, a first layer 620 having conventional QDs disposed on the bottom electrode 610, and a second layer 630 having 2D QDs disposed on the first layer 620 containing conventional QDs, and a top electrode 640 disposed on the second layer 630 containing 2D QDs. In this configuration, one or more of the top and bottom electrodes 610, 640 may be transparent to allow light to enter the device. To form a heterojunction, the first layer 620 containing conventional QDs and the second layer 630 containing 2D QDs are selected so that the conduction band and valence band of the conventional QDs deviate from the conduction band and valence band of the 2D QDs. This can be achieved by selecting conventional QDs and 2D QDs of materials with different semiconductor bandgaps, and / or adjusting the diameter of the conventional QDs, and / or adjusting the lateral size of the 2D QDs, and / or adjusting the thickness of the 2D QDs, and / or functionalizing the surface of one or both of the 2D QDs and conventional 2D QDs with different ligands that change the bandgaps of the materials. The junction width can control the wavelength of light absorbed.

[0074] The composition and / or thickness of the conventional QD-containing layer 620 and the 2D QD-containing layer 630 can vary as described above for the conventional QD-containing layer 520 and the 2D QD-containing layer 520, respectively. Preferably, the combined thickness of the conventional QD-containing layer 620 and the 2D QD-containing layer 630 is from about 50 nm to about 800 nm, more preferably from about 100 nm to about 700 nm, and even more preferably from about 200 nm to about 600 nm. In some cases, each of the conventional QD-containing layer 620 and the 2D QD-containing layer 630 has the same or substantially the same thickness. In other cases, the QD-containing layer 620 is thicker than the 2D QD-containing layer 630. In other cases, the 2D QD-containing layer 630 is thicker than the QD-containing layer 620.

[0075] In some cases, the heterostructure photodetector 600 may also include an intermediate layer (not shown) disposed between the bottom electrode 610 and the conventional QD-containing layer 620. The intermediate layer may be made of the same material as the intermediate layer 220 of the photodetector 200. Figure 6 , a layer 620 containing conventional QDs and a layer 630 containing 2D QDs are shown as separate layers. In some cases, a transition layer (not shown) may be disposed between the layer 620 containing conventional QDs and the layer 630 containing 2D QDs, the transition layer having a combination of conventional QDs (i.e., conventional QDs of layer 620) and 2D QDs (i.e., 2D QDs of layer 630). In some cases, the relative amounts of conventional QDs and 2D QDs may be uniform or substantially uniform throughout the thickness of the transition layer. In some cases, the transition layer may exhibit a gradient in which the amount of conventional QDs decreases from the layer 620 containing conventional QDs to the layer 630 containing 2D QDs. In some cases, the transition layer may exhibit a gradient in which the amount of 2D QDs increases from the layer 620 containing conventional QDs to the layer 630 containing 2D QDs.

[0076] Figure 7is a schematic diagram of a heterostructure photodetector 700 according to aspects of the present disclosure. The heterostructure photodetector 700 includes a bottom electrode 710, and a first layer 720 with 2D QDs disposed on the bottom electrode 710, a second layer 730 with 2D nanosheets disposed on the first layer 720 containing 2D QDs, and a top electrode 740 disposed on the second layer 730 containing 2D nanosheets. In this configuration, one or more of the top and bottom electrodes 710, 740 can be transparent to allow light to enter the device. To form a heterojunction, the 2D QDs and 2D nanosheets in the layers 720, 730 are aligned so that the conduction band and valence band of the 2D QDs deviate from the conduction band and valence band of the 2D nanosheets to form a built-in electric field. This can be achieved by selecting 2D QD and 2D nanosheet materials with different semiconductor bandgaps, and / or adjusting the lateral size of the second 2D QD and / or 2D nanosheet, and / or adjusting the thickness of the 2D QD and / or 2D nanosheet, and / or functionalizing the surface of one or both of the 2D QD and 2D nanosheet with different ligands that change the bandgaps of the materials. The junction width can control the wavelength of light absorbed.

[0077] The composition and / or thickness of the layer 720 containing 2D QDs and the layer 730 containing 2D nanosheets can be varied as described above for the layer 330 containing 2D QDs and the layer 320 containing 2D nanosheets, respectively. Preferably, the combined thickness of the layer 720 containing 2D QDs and the layer 730 containing 2D nanosheets is from about 50 nm to about 800 nm, more preferably from about 100 nm to about 700 nm, and even more preferably from about 200 nm to about 600 nm. In some cases, each of the layer 720 containing 2D QDs and the layer 730 containing 2D nanosheets has the same or substantially the same thickness. In other cases, the layer 720 containing 2D QDs is thicker than the layer 730 containing 2D nanosheets. In other cases, the layer 730 containing 2D nanosheets is thicker than the layer 720 containing 2D QDs.

[0078] In some cases, the heterostructure photodetector 700 may further include an intermediate layer (not shown) disposed between the bottom electrode 710 and the layer 720 containing 2DQDs. The intermediate layer may be made of the same material as the intermediate layer 220 of the photodetector 200. Figure 7, a layer 720 containing 2D QDs and a layer 730 containing 2D nanosheets are shown as separate layers. In some cases, a transition layer (not shown) may be disposed between the layer 720 containing 2D QDs and the layer 730 containing 2D nanosheets, the transition layer having a combination of 2D QDs (i.e., the 2D QDs of the layer 720) and 2D nanosheets (i.e., the 2D nanosheets of the layer 730). In some cases, the relative amounts of 2D QDs and 2D nanosheets may be uniform or substantially uniform over the entire thickness of the transition layer. In some cases, the transition layer may exhibit a gradient in which the amount of 2D QDs decreases from the layer 720 containing 2D QDs to the layer 730 containing 2D nanosheets. In some cases, the transition layer may exhibit a gradient in which the amount of 2D nanosheets increases from the layer 720 containing 2D QDs to the layer 730 containing 2D nanosheets.

[0079] 2D QDs according to aspects of the present disclosure can be colloidally synthesized and deposited via solution processing. Suitable 2D QD materials include, but are not limited to:

[0080] Graphene, graphene oxide and reduced graphene oxide;

[0081] TMDCs, such as, for example, WO2; WS2; WSe2; WTe2; MnO2; MoO2; MoS2; MoSe2; MoTe2; NiO2; NiTe2; NiSe2; VO2; VS2; VSe2; TaS2; TaSe2; RuO2; RhTe2; PdTe2; HfS2; NbS2; NbSe2; NbTe2; FeS2; TiO2; TiS2; TiSe2; and ZrS2;

[0082] Transition metal trichalcogenides, such as, for example, TaO3; MnO3; WO3; ZrS3; ZrSe3; HfS3; and HfSe3;

[0083] Group 13-16 (III-VI) compounds, such as, for example, InS; InSe; GaS; GaSe; and GaTe;

[0084] Group 15-16 (IV-VI) compounds, such as, for example, Bi2Se3; and B i2 Te3;

[0085] Nitrides, such as, for example, h-BN;

[0086] Oxides, such as LaVO3; LaMnO3; V2O5; LaNbO7; Ca2Nb3O 10 ; Ni(OH)2; and Eu(OH)2; layered copper oxides; mica; and bismuth strontium calcium copper oxide (BSCCO);

[0087] Phosphides, such as, for example, Li7MnP4; and MnP4; and

[0088] 2D allotropes of Group 14 elements, such as, for example, silicone; germanene; and stanene.

[0089] In the foregoing materials, adjacent layers are held together by van der Waals interactions, which can be easily broken by techniques such as exfoliation techniques (e.g., liquid phase exfoliation (LPE)) to form 2D flakes. In alternative embodiments, 2D QDs may include traditionally non-layered semiconductor materials, including but not limited to:

[0090] Group 12-16 (II-VI) semiconductors, such as, for example, ZnS; ZnSe; CdS; CdSe; CdTe;

[0091] Group 13-15 (III-V) materials, such as, for example, AlN, AlP, AlAs, GaN; GaP; GaAs; InN; InP; InAs;

[0092] Group 15-16 (V-VI) materials, such as, for example, PbS, PbSe, PbTe; and

[0093] Group I-III-VI materials, such as, for example, CuGaS2; CuGaSe2; CuGa(S,Se)2; CuInS2, CuInSe2; CuIn(S,Se)2; Cu(In,Ga)S2; Cu(In,Ga)Se2; Cu(In,Ga)(S,Se)2; CuInTe2; AgInS2; and AgInSe2, including their dopants and alloys.

[0094] For example, 2D QDs of the aforementioned materials can be formed via physical or chemical cutting methods. Specifically, zero-dimensional (0D), one-dimensional (1D) or three-dimensional (3D) of the desired shape, size and composition can be formed, followed by treatment, such as chemical treatment, such as reflow, LPE and reflow or intercalation and stripping, to form uniformly sized 2D QDs according to the inherent shape of the 3D or OD nanoparticles. The method is scalable and can be used for mass production of 2D QDs with uniformity. As used herein, "cutting" of nanoparticles means separating the nanoparticles into two or more parts. The term is not intended to imply any limitation on the separation method and may include physical and chemical methods of separation. Physical separation methods may include, but are not limited to: mechanical stripping (so-called "Scotch tape method"), delamination, grinding and mixing. As used herein, "chemical cutting" of nanoparticles means separating the nanoparticles into two or more parts, wherein the separation is achieved by chemical treatment. In certain embodiments, chemical treatment may include: applying heat, pressure, vacuum, ultrasound and / or stirring to a solution or dispersion of nanoparticles; chemical etching; and intercalation. Non-limiting examples of chemical cleavage methods include: refluxing the nanoparticles in solution; LPE of the nanoparticles followed by refluxing; or intercalation and exfoliation of the nanoparticles.

[0095] Any suitable technique can be used to cut 0D, 1D or 3D nanoparticles into 2D QDs. Suitable examples include chemical and physical stripping methods. In one embodiment, the cutting of prefabricated nanoparticles is carried out by chemical methods such as LPE, which includes ultrasonic treatment of prefabricated nanoparticles in a solvent. The surface tension of the solvent can be selected to match the material to be stripped. In some embodiments, the stripped nanoparticles are subsequently refluxed in solution.

[0096] In some embodiments, the cutting of 0D, 1D or 3D nanoparticles can be performed by refluxing the prefabricated nanoparticles in the solution without prior peeling. Those of ordinary skill in the art will recognize that the reflux temperature of the 0D, 1D or 3D nanoparticle solution will depend on the boiling point of the solvent in which the solution is formed. Without wishing to be limited by any particular theory, a possible mechanism is that the application of heat can cause the layers within the 0D, 1D or 3D nanoparticles to thermally expand; refluxing the solution can form a gas that chemically cuts the layers apart. In some embodiments, the solution includes a coordinating solvent. Examples of suitable coordinating solvents include, but are not limited to, saturated alkyl amines, such as, for example, C6-C 50Alkylamines; unsaturated fatty amines, such as, for example, oleylamine; fatty acids, such as, for example, myristic acid, palmitic acid, and oleic acid; phosphines, such as, for example, trioctylphosphine (TOP); phosphine oxides, such as, for example, trioctylphosphine oxide (TOPO); alcohols, such as, for example, hexadecanol, benzyl alcohol, ethylene glycol, propylene glycol; and may include primary, secondary, tertiary, and branched solvents. In some embodiments, the solution includes a non-coordinating solvent, such as, but not limited to, C 11 -C 50 Alkanes. In some embodiments, the boiling point of the solvent is from 150° C. to 600° C., such as from 160° C. to 400° C., or more specifically from 180° C. to 360° C. In a particular embodiment, the solvent is hexadecylamine.

[0097] In other embodiments, the cutting of the preformed nanoparticles is performed by an intercalation and stripping method. The intercalation and stripping of TMDC multilayer nanostructures can be completed using a Lewis base intercalation method. The first intercalation and stripping process can be performed in the following manner: the preformed nanoparticles are stirred in a first solvent for a first time period in the presence of a first intercalation agent and a second intercalation agent. Optionally, a second solvent can be subsequently added and then stirred for a second time period. In some embodiments, the second intercalation and stripping process is performed in the following manner: the product of the first intercalation and stripping process is mixed with a third intercalation agent and a third solvent and stirred for a third time period. Optionally, a fourth solvent can be subsequently added and then stirred for a fourth time period. The first intercalation agent and the second intercalation agent may include hydrocarbon compounds, wherein the hydrocarbon chain length of the first intercalation agent is different from the hydrocarbon chain length of the second intercalation agent. The third intercalation agent may be the same or different from the first and / or second intercalation agent. Suitable first, second and third intercalation agents may include, but are not limited to:

[0098] Lewis bases, such as amines, such as, for example, propylamine, hexylamine; alkoxides, such as, for example, sodium methoxide, sodium ethoxide; carboxylates, such as, for example, sodium hexanoate; and amino alcohols, such as, for example, 3-amino-1-propanol;

[0099] Aminothiols, such as, for example, mercaptoethylamine, 6-amino-1-hexanethiol and 8-amino-1-octanethiol;

[0100] Amino acids, including alkyl amino acids, such as, for example, 3-aminopropionic acid (β-alanine), 6-aminocaproic acid, 8-aminooctanoic acid; and

[0101] Metal salts, such as, for example, having the general formula MX n Those wherein M is Mo, Cd, Zn or In and X is a halide ion (especially Cl - Br - and I - ), acetate, octanoate, palmitate, laurate, myristate or oleate. Another suitable metal salt is [MoCl5]2.

[0102] Typically, the choice of one or more solvents in which the intercalation and stripping processes are performed will depend on the choice of nanoparticles and intercalation agents. During intercalation and stripping, it is desirable that the nanoparticles are fully dispersed or dissolved in one or more solvents. It is also desirable that the one or more intercalation agents are soluble in one or more solvents. The second solvent may be different from the first solvent. The third solvent may be the same as the first solvent or the second solvent, or may be different from both the first solvent and the second solvent. In some cases, suitable solvents include polar aprotic solvents, such as, for example, dimethyl sulfoxide (DMSO), N-methylformamide (NMF) and acetonitrile. In some cases, suitable solvents include polar protic solvents, such as, for example, propanol and isopropanol.

[0103] The first time period can be in the range of about 1 hour to about 1 month, alternatively about 2 hours to about 2 weeks and alternatively about 4 hours to about 3 days. The second time period can be in the range of about 1 hour to about 2 months, alternatively about 2 days to about 2 weeks and alternatively about 1 week to about 3 weeks. The third time period can be in the range of about 1 hour to about 1 month, alternatively about 2 hours to about 2 weeks and alternatively about 4 hours to about 3 days. The fourth time period can be in the range of about 1 hour to about 2 months, alternatively about 2 days to about 2 weeks and alternatively about 1 week to about 3 weeks. Generally, the time period will depend on factors such as the following: the selection of one or more solvents and one or more intercalation agents, the strength of the bonding in the nanoparticles and the concentration of the nanoparticles in the solvent relative to the intercalation agent, and a longer time period can obtain a higher 2D nanosheet yield.

[0104] In some embodiments, the first and / or second and / or subsequent intercalation and exfoliation processes can be achieved using ultrasonic treatment.Using ultrasonic treatment instead of stirring can help shorten one or more time periods required to achieve the chemical cutting process.

[0105] Other cutting techniques can be used to cut 0D, 1D or 3D nanoparticles into 2D QDs, such as but not limited to etching techniques. According to a specific embodiment, the 2D QDs can then be separated from the solution by techniques such as but not limited to centrifugation; filtration; dialysis or column chromatography. The resulting 2D nanosheets can be dispersed in a solvent to form an ink, which can be deposited using conventional solution-based deposition techniques to form a film, such as but not limited to: drop casting, spin coating, slit coating, spraying, slit dye coating, inkjet printing or doctor blade coating. The inherent uniformity in the properties of 2D QDs can result in a high degree of uniformity in the resulting film. The film thickness can be controlled by, for example, changing the concentration of the ink and / or by changing the size of the 2D QDs.

[0106] The layer of 2D nanosheets can be formed using techniques such as, but not limited to, mechanical exfoliation, chemical vapor deposition (CVD), atomic layer deposition (ALD); molecular beam epitaxy (MBE); lateral heteroepitaxy; and vapor-solid growth. Suitable 2D nanosheets for the layer containing 2D nanosheets include, but are not limited to:

[0107] Graphene, graphene oxide and reduced graphene oxide;

[0108] TMDCs, such as, for example, WO2; WS2; WSe2; WTe2; MnO2; MoO2; MoS2; MoSe2; MoTe2; NiO2; NiTe2; NiSe2; VO2; VS2; VSe2; TaS2; TaSe2; RuO2; RhTe2; PdTe2; HfS2; NbS2; NbSe2; NbTe2; FeS2; TiO2; TiS2; TiSe2; and ZrS2;

[0109] Transition metal trichalcogenides, such as, for example, TaO3; MnO3; WO3; ZrS3; ZrSe3; HfS3; and HfSe3;

[0110] Group 13-16 (III-VI) compounds, such as, for example, InS; InSe; GaS; GaSe; and GaTe;

[0111] Group 15-16 (IV-VI) compounds, such as, for example, Bi2Se3; and Bi2Te3;

[0112] Nitrides, such as, for example, h-BN;

[0113] Oxides, such as LaVO3; LaMnO3; V2O5; LaNbO7; Ca2Nb3O 10 ; Ni(OH)2; and Eu(OH)2; layered copper oxides; mica; and BSCCO;

[0114] Phosphides, such as, for example, Li7MnP4; and MnP4; and

[0115] 2D allotropes of Group 14 elements, such as, for example, silicene; germanene; and stanene.

[0116] For devices containing a layer of conventional QDs, the QD layer may be formed from materials including, but not limited to, the following:

[0117] IIA-VIB (2-16) materials consisting of a first element from Group 2 of the periodic table and a second element from Group 16 of the periodic table, and also including ternary and quaternary materials and doped materials. Nanoparticle materials include, but are not limited to: MgS, MgSe, MgTe, CaS, CaSe, CaTe, SrS, SrSe, SrTe, BaS, BaSe, BaTe;

[0118] IIB-VIB (12-16) materials, which consist of a first element from Group 12 of the periodic table and a second element from Group 16 of the periodic table, and also include ternary and quaternary materials and doped materials. Nanoparticle materials include, but are not limited to: ZnS, ZnSe, ZnTe, CdS, CdSe, CdTe, HgS, HgSe, HgTe;

[0119] II-V materials consisting of a first element from Group 12 of the periodic table and a second element from Group 15 of the periodic table, and also including ternary and quaternary materials and doped materials. Nanoparticle materials include, but are not limited to: Zn3P2, Zn3As2, Cd3P2, Cd3As2, Cd3N2, Zn3N2;

[0120] III-V materials consisting of a first element from group 13 of the periodic table and a second element from group 15 of the periodic table, and also including ternary and quaternary materials and doped materials. Nanoparticle materials include, but are not limited to: BP, AlP, AlAs, AlSb; GaN, GaP, GaAs, GaSb; InN, InP, InAs, InSb, AlN, BN;

[0121] III-IV materials consisting of a first element from Group 13 of the periodic table and a second element from Group 14 of the periodic table, and also including ternary and quaternary materials and doped materials. Nanoparticle materials include, but are not limited to: B4C, Al4C3, Ga4C;

[0122] III-VI materials consisting of a first element from Group 13 of the periodic table and a second element from Group 16 of the periodic table, and also including ternary and quaternary materials. Nanoparticle materials include, but are not limited to: Al2S3, Al2Se3, Al2Te3, Ga2S3, Ga2Se3, GeTe; In2S3, In2Se3, Ga2Te3, In2Te3, InTe;

[0123] IV-VI materials consisting of a first element from Group 14 of the periodic table and a second element from Group 16 of the periodic table, and also including ternary and quaternary materials and doped materials. Nanoparticle materials include, but are not limited to: PbS, PbSe, PbTe, SnS, SnSe, SnTe;

[0124] V-VI materials consisting of a first element from Group 15 of the periodic table and a second element from Group 16 of the periodic table, and also including ternary and quaternary materials and doped materials. Nanoparticle materials include, but are not limited to: Bi2Te3, Bi2Se3, Sb2Se3, Sb2Te3; and

[0125] Nanoparticle materials consisting of a first element from any group of transition metals in the periodic table and a second element from group 16 of the periodic table, and also including ternary and quaternary materials and doped materials. Nanoparticle materials include, but are not limited to: NiS, CrS, CuInS2, AgInS2.

[0126] In some cases, in heterostructure devices according to aspects of the present disclosure, the relative bandgaps of the semiconductor materials can be selected to form a Type I heterostructure, such as a WSe2 2D QD with a MoTe2 2D QD layer or a MoTe2 2D nanosheet layer. In some cases, the relative bandgaps of the semiconductor materials can be selected to form a Type II heterostructure, such as a PbS QD with a WSe2 2D QD layer, or a MoS2 2D QD with a WSe2 2D QD layer or a WSe2 nanosheet layer.

[0127] In some cases, the thickness of one or more of the 2D layers can be a single monolayer. Making the sensitizer as thin as possible can be beneficial to maximize charge screening effects, flexibility, and device transparency. A thickness close to the absorption depth may be desirable to maximize the absorption of incident light. However, for stronger absorption, thicker devices may also be required. Adjusting the thickness of the material also provides a means of controlling its band gap. Therefore, in some cases, one or more of the 2D layers can be 1-5 monolayers. In some cases, the 2D nanosheet layer can be a monolayer. Compared to a few layers or bulk materials, a monolayer can provide advantageous properties. For example, transition metal dichalcogenides exhibit a transition from an indirect band gap to a direct band gap when a monolayer is formed.

[0128] A variety of strategies can be implemented to enhance charge transport within the 2D QD layer. For example, the inherent 2D QD ligands can be replaced with shorter chain ligands. As used herein, "short-chain ligands" refer to ligands with hydrocarbon chains of eight carbons or less. Suitable short-chain ligands include, but are not limited to, alkanethiols such as 1-octanethiol, 1-heptylthiol, 1-hexylthiol, 1-pentylthiol, 1-butanethiol, 1-propanethiol; alkylamines such as methylamine, ethylamine, propylamine, butylamine, octylamine, allylamine; and carboxylic acids such as octanoic acid, heptanoic acid, hexanoic acid, pentanoic acid, butyric acid, and propionic acid. Other suitable ligands may include pyridine and pyrrolidone. In some cases, bridging ligands may be used to improve connectivity between adjacent 2D QDs. Suitable examples include, but are not limited to, bidentate ligands such as ethanedithiol or 3-mercaptopropionic acid.

[0129] Another strategy to improve the connectivity between 2D QDs can include the use of chalcogen ligands. In this method, by removing organic surface ligands and passivating the QD surface with chalcogen ligands, the QDs can be "necked". In some cases, adjacent QDs can be fused. A film can be formed using fused 2D QDs, wherein the 2D QDs include ligands on the unfused portions of their outer surfaces. Fusion can cause the 2D QDs to substantially maintain their respective properties while being connected via regions through which current can easily flow. In one embodiment, the synthesized 2D QDs can be ligand exchanged to replace the intrinsic ligands with shorter, more volatile ligands. The ligand-exchanged 2D QDs can then be solution deposited, and the short-chain ligands are then removed to bring the 2D QDs very close together, so that some of the 2D QDs are in contact with their neighbors. This is called "necking". Subsequently, the necked 2D QDs can be annealed to fuse the 2D QDs together. Typically, the fused 2D QDs and the connections between them will not contain defect states, which allows current to flow easily between them.

[0130] When conventional QDs are used (such as in conventional QD-containing layer 530 of photodetector 500 or conventional QD-containing layer 620 of photodetector 600), the conventional QDs may be core, core-shell, or core-multi-shell QDs with a size in the range of 2-100 nm. The material of the core may include:

[0131] IIA-VIA (2-16) materials consisting of a first element from Group 2 of the periodic table and a second element from Group 16 of the periodic table, and also including ternary and quaternary materials and doped materials. Nanoparticle materials include, but are not limited to: MgS, MgSe, MgTe, CaS, CaSe, CaTe, SrS, SrSe, SrTe, BaS, BaSe, BaTe;

[0132] IIB-VIA (12-16) materials, which consist of a first element from Group 12 of the periodic table and a second element from Group 16 of the periodic table, and also include ternary and quaternary materials and doped materials. Nanoparticle materials include, but are not limited to: ZnO, ZnS, ZnSe, ZnTe, CdS, CdSe, CdTe, HgS, HgSe, HgTe;

[0133] II-V materials consisting of a first element from Group 12 of the periodic table and a second element from Group 15 of the periodic table, and also including ternary and quaternary materials and doped materials. Nanoparticle materials include, but are not limited to: Zn3P2, Zn3As2, Cd3P2, Cd3As2, Cd3N2, Zn3N2;

[0134] III-V materials consisting of a first element from group 13 of the periodic table and a second element from group 15 of the periodic table, and also including ternary and quaternary materials and doped materials. Nanoparticle materials include, but are not limited to: BP, AlP, AlAs, AlSb; GaN, GaP, GaAs, GaSb; InN, InP, InAs, InSb, AlN, BN;

[0135] III-IV materials consisting of a first element from Group 13 of the periodic table and a second element from Group 14 of the periodic table and also including ternary and quaternary materials and doped materials. Nanoparticle materials include, but are not limited to: B4C, A14C3, Ga4C;

[0136] III-VI materials consisting of a first element from Group 13 of the periodic table and a second element from Group 16 of the periodic table, and also including ternary and quaternary materials. Nanoparticle materials include, but are not limited to: Al2S3, Al2Se3, Al2Te3, Ga2S3, Ga2Se3, GeTe; In2S3, In2Se3, Ga2Te3, In2Te3, InTe;

[0137] IV-VI materials consisting of a first element from Group 14 of the periodic table and a second element from Group 16 of the periodic table, and also including ternary and quaternary materials and doped materials. Nanoparticle materials include, but are not limited to: PbS, PbSe, PbTe, SnS, SnSe, SnTe;

[0138] V-VI materials consisting of a first element from Group 15 of the periodic table and a second element from Group 16 of the periodic table, and also including ternary and quaternary materials and doped materials. Nanoparticle materials include, but are not limited to: Bi2Te3, Bi2Se3, Sb2Se3, Sb2Te3; and

[0139] Nanoparticle materials consisting of a first element from any group of transition metals in the periodic table and a second element from group 16 of the periodic table, and also including ternary and quaternary materials and doped materials. Nanoparticle materials include, but are not limited to: NiS, CrS, CuInS2, AgInS2.

[0140] For the purpose of the specification and claims, the term doped nanoparticles refers to the above nanoparticles and a dopant consisting of one or more main group or rare earth elements, most commonly transition metals or rare earth elements, such as but not limited to zinc sulfide with manganese, such as zinc sulfide doped with Mn + ZnS nanoparticles.

[0141] For the purpose of the specification and claims, the term "ternary material" refers to the above QDs, but as three-component materials. The three components are usually a combination of elements from the above groups, examples being (Zn x Cd x-1 S) m L n Nanocrystals (wherein L is a capping agent).

[0142] For the purpose of the specification and claims, the term "quaternary material" refers to the above nanoparticles, but it is a four-component material. The four components are usually a combination of elements from the above groups, examples are (Zn x Cd x-1 S y Se y-l ) m L n Nanocrystals (wherein L is a capping agent).

[0143] In most cases, the material for any shell or subsequent number of shells grown on a conventional QD core will have a lattice type material similar to the core material, i.e., a material with a high degree of lattice match to the core material so that it can be epitaxially grown on the core, but is not necessarily limited to materials of such compatibility. In most cases, the material for any shell or subsequent number of shells grown on an existing core will have a wider band gap than the core material, but is not necessarily limited to materials of such compatibility. The material for any shell or subsequent number of shells grown on a core includes materials, which include:

[0144] IIA-VIA (2-16) materials consisting of a first element from Group 2 of the periodic table and a second element from Group 16 of the periodic table, and also including ternary and quaternary materials and doped materials. Nanoparticle materials include, but are not limited to: MgS, MgSe, MgTe, CaS, CaSe, CaTe, SrS, SrSe, SrTe;

[0145] IIB-VIA (12-16) materials, which consist of a first element from Group 12 of the periodic table and a second element from Group 16 of the periodic table, and also include ternary and quaternary materials and doped materials. Nanoparticle materials include, but are not limited to: ZnS, ZnSe, ZnTe, CdS, CdSe, CdTe, HgS, HgSe, HgTe;

[0146] II-V materials consisting of a first element from Group 12 of the periodic table and a second element from Group 15 of the periodic table, and also including ternary and quaternary materials and doped materials. Nanoparticle materials include, but are not limited to: Zn3P2, Zn3As2, Cd3P2, Cd3As2, Cd3N2, Zn3N2;

[0147] III-V materials consisting of a first element from group 13 of the periodic table and a second element from group 15 of the periodic table, and also including ternary and quaternary materials and doped materials. Nanoparticle materials include, but are not limited to: BP, AlP, AlAs, AlSb; GaN, GaP, GaAs, GaSb; InN, InP, InAs, InSb, AlN, BN;

[0148] III-IV materials consisting of a first element from Group 13 of the periodic table and a second element from Group 14 of the periodic table, and also including ternary and quaternary materials and doped materials. Nanoparticle materials include, but are not limited to: B4C, A14C3, Ga4C;

[0149] III-VI materials consisting of a first element from Group 13 of the periodic table and a second element from Group 16 of the periodic table, and also including ternary and quaternary materials. Nanoparticle materials include, but are not limited to: Al2S3, Al2Se3, Al2Te3, Ga2S3, Ga2Se3, In2S3, In2Se3, Ga2Te3, In2Te3;

[0150] IV-VI materials consisting of a first element from Group 14 of the periodic table and a second element from Group 16 of the periodic table, and also including ternary and quaternary materials and doped materials. Nanoparticle materials include, but are not limited to: PbS, PbSe, PbTe, SnS, SnSe, SnTe;

[0151] V-VI materials consisting of a first element from Group 15 of the periodic table and a second element from Group 16 of the periodic table, and also including ternary and quaternary materials and doped materials. Nanoparticle materials include, but are not limited to: Bi2Te3, Bi2Se3, Sb2Se3, Sb2Te3; and

[0152] Nanoparticle materials consisting of a first element from any group of transition metals in the periodic table and a second element from group 16 of the periodic table, and also including ternary and quaternary materials and doped materials. Nanoparticle materials include, but are not limited to: NiS, CrS, CuInS2, AgInS2.

[0153] The aforementioned strategies for increasing connectivity within 2D QD layers can also be applied to conventional QD layers.

[0154] Photodetector devices according to aspects of the present disclosure can be integrated with complementary metal-oxide-semiconductor (CMOS) circuits. Devices including 2D QDs can be fabricated using CMOS technology, for example by spin coating a 2D QD layer onto a prefabricated CMOS electronic readout circuit. Integration into CMOS circuits may be desirable to form small pixels, thereby enabling high-resolution sensors.

[0155] In some cases, multiple pixels with spectral sensitivities in different regions can be monolithically integrated. The spectral sensitivity of each pixel can be tuned by varying the lateral size and / or thickness of the 2D QDs.

[0156] In some cases, the phototransistor device according to aspects of the present disclosure can be gated. Gating acts as a control mechanism and allows for increased functionality because the gate voltage can be varied to act as a switch or amplifier. In particular, the high carrier mobility of 2D materials can be advantageous because the gain is proportional to the carrier mobility.

[0157] The foregoing presents specific embodiments that embody the principles of the present invention. Those skilled in the art will be able to design alternatives and variations that, even if not explicitly disclosed herein, embody those principles and are therefore within the scope of the present invention. Although specific embodiments of the present invention have been shown and described, they are not intended to limit the content covered by this patent. Those skilled in the art will appreciate that, as literally and equally covered by the appended claims, various changes and modifications can be made without departing from the scope of the present invention.

Claims

1. A heterostructure photodetector, the heterostructure photodetector include: a first electrode; a first light absorbing layer disposed on the first electrode, the first light absorbing layer comprising a first light absorbing material; a second light absorbing layer disposed on the first light absorbing layer, the second light absorbing layer comprising a second light absorbing material; as well as a second electrode disposed on the second light absorbing layer; wherein at least one of the first light absorbing material and the second light absorbing material is a plurality of two-dimensional quantum dots (2D QDs); Each of the 2D QDs has a thickness of 1 to 5 atomic or molecular monolayers and a lateral size sufficient to keep the 2D QD within quantum confinement; and The 2D QD is made of a material selected from the following: transition metal dichalcogenides, transition metal trichalcogenides, nitrides, oxides, phosphides, Group 12-16 semiconductor compounds, Group 13-15 semiconductor compounds, Group 15-16 semiconductor compounds, CuGaS 2 , CuGaSe 2 , CuGa(S,Se) 2 , CuInS 2 , CuInSe 2 , CuIn(S,Se) 2 , Cu(In,Ga)S 2 , Cu(In,Ga)Se 2 , Cu(In,Ga)(S,Se) 2 、CuInTe 2 、AgInS 2 and AgInSe 2 ;as well as A heterojunction is formed between the first light absorbing layer and the second light absorbing layer, wherein the valence band and conduction band of the first light absorbing material deviate from the valence band and conduction band of the second light absorbing material to generate a built-in electric field. 2 . The heterostructure photodetector according to claim 1 , further comprising an intermediate layer disposed between the first electrode and the first light absorbing layer. 3 . The heterostructure photodetector according to claim 1 , further comprising a transition layer disposed between the first light absorbing layer and the second light absorbing layer, the transition layer comprising a combination of the first light absorbing material and the second light absorbing material.

4. The heterostructure photodetector according to claim 1, wherein the first light absorbing material is a plurality of two-dimensional quantum dots (2D QDs), a plurality of two-dimensional nanosheets (2D nanosheets), or a plurality of conventional QDs. 5 . The heterostructure photodetector according to claim 1 , wherein the second light absorbing material is a plurality of 2D QDs, a plurality of 2D nanosheets, or a plurality of conventional QDs. 6 . The heterostructure photodetector of claim 1 , wherein the first light absorbing material is a plurality of 2D nanosheets and the second light absorbing material is a plurality of 2D QDs. 7 . The heterostructure photodetector of claim 1 , wherein the first light absorbing material is a plurality of first 2D QDs and the second light absorbing material is a plurality of second 2D QDs.

8. The heterostructure photodetector of claim 1, wherein the first light absorbing material is a plurality of 2D QDs and the second light absorbing material is a plurality of conventional QDs.

9. The heterostructure photodetector of claim 1, wherein the first light absorbing material is a plurality of conventional QDs and the second light absorbing material is a plurality of 2D QDs.

10. The heterostructure photodetector of claim 1, wherein the first light absorbing material is a plurality of 2D QDs and the second light absorbing material is a plurality of 2D nanosheets. 11 . The heterostructure photodetector of claim 1 , wherein a combined thickness of the first light absorbing layer and the second light absorbing layer is in a range of 50 nm to 800 nm. 12 . The heterostructure photodetector of claim 1 , wherein one of the first light absorbing layer and the second light absorbing layer further comprises a charge transport material.

13. The heterostructure photodetector of claim 1, wherein one of the first light absorbing material and the second light absorbing material is a plurality of 2D nanosheets having a thickness of 1 to 10 atomic or molecular monolayers and a lateral dimension extending beyond the quantum confinement range.

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