An organic photodiode and an array thereof and a method for preparing the organic photodiode

Abstract

The present invention relates to a highly sensitive organic photodiode, which includes a photosensitive layer, wherein the photosensitive layer is a bulk heterojunction structure, that is, (i) including a donor material D1 and an acceptor material A1; and a donor material D2-Dn; and the energy gap of the donor material D2-Dn is greater than the energy gap of the donor material D1 and / or the energy gap of the acceptor material A1; or (ii) including a donor material D1 and an acceptor material A1; and an acceptor material A2-An; and the energy gap of the acceptor material A2-An is greater than the energy gap of the donor material D1 and / or the energy gap of the acceptor material A1. The addition of new components in the photosensitive layer effectively reduces the density of impurity defect states in the bulk heterojunction energy gap, suppresses the trap-assisted recombination channel of photogenerated charges, enhances the external quantum efficiency, reduces the dark current, and thus improves the specific detection rate of the device. The present invention also relates to an array composed thereof and a related preparation method.

Description

Technical Field

[0001] The invention belongs to the field of organic photoelectric detectors, and in particular relates to a highly sensitive organic photodiode and an array formed by the organic photodiode, and a method for preparing the organic photodiode. Background Art

[0002] Organic photodiodes, and arrays made of them, are expected to be used in emerging fields such as machine vision, health monitoring, and biometrics. However, although silicon single crystal-based photodiodes have been widely used as key components of image sensors, they still have poor infrared response and complex manufacturing processes, which leads to high preparation costs and limits their further application. Traditional forward-incident complementary metal oxide semiconductor (CMOS) image sensors have a rapid decrease in near-infrared light response efficiency of 700-1000nm due to their thinner photosensitive layers. The external quantum efficiency (EQE) of monochrome image sensors (such as SONY IMX250) at 850nm and 940nm wavelengths is only 18% and 7% (refer to FLIR's image sensor product guide, https: / / www.flir.com / discover / iis / machine-vision / pregius-s).

[0003] On the one hand, in order to improve the light response in the near-infrared region, relevant teams have recently developed back-incident CMOS image sensor arrays, and also developed technologies to integrate photosensitive pixel arrays made of silicon on insulating substrates (SOI) with CMOS readout arrays. However, these image arrays require deep trench etching and complex post-processing processes, which limits the pixel pitch, process yield and device cost of image sensors. Furthermore, even if the above defects are improved, the EQE of these CMOS arrays at a wavelength of 940nm is still less than 30%.

[0004] On the other hand, image sensors for the short-wave infrared (SWIR) band (1000-1700nm) have so far been produced using a hybrid technology in which arrays of photodetectors based on III-V single crystals (usually based on InGaAs) are flip-chip connected to a silicon-based readout circuit. These sensors are very sensitive when operating at low temperatures, but are difficult to use for room temperature measurements due to their high dark conductance, especially in low light conditions. Photodetectors based on III-V single crystals are very expensive for mass production and are limited in pixel size and number of pixels, hindering their use in markets where cost, resolution and / or form factor are critical.

[0005] As an alternative material, organic semiconductors have good mechanical flexibility, adjustable absorption spectrum and easy integration into CMOS or thin-film transistor (TFT) backplanes, providing new opportunities in the fields of wearable electronic devices and artificial intelligence. In the past 20 years, the dark current of organic photodiodes responsive to visible light has been reduced to sub-nA / cm 2 However, for short-wave infrared organic photodiodes with spectral response in the near-infrared band or even above 1000nm, such low dark current density has not been reported. This is because as the material energy gap decreases, the thermal excitation of charges begins to have a non-negligible effect on the dark current. In addition, the charge injection caused by pinholes and defects in the thin film photosensitive layer makes the short-wave infrared organic photodiode have inherent noise and detection rate limitations. In addition, the narrowing of the energy gap also reduces the driving force for exciton dissociation, making it difficult to achieve high external quantum efficiency.

[0006] Therefore, how to make organic photodiodes achieve the characteristics of low dark current and high responsiveness at the same time remains a topic to be developed. Summary of the invention

[0007] The purpose of the present invention is to disclose a highly sensitive organic photodiode and an array thereof, wherein the highly sensitive organic photodiode has extremely high responsiveness and extremely low dark current in the near infrared and short-wave infrared regions, and can greatly improve the organic photodiode's ability to detect weak light in the infrared region. The present invention also relates to a method for preparing the organic photodiode.

[0008] The term "bulk heterojunction structure" in the present invention refers to an interpenetrating network structure with nanoscale phase separation formed by blending donor and acceptor materials.

[0009] The term "donor material" in the present invention refers to a P-type organic semiconductor material.

[0010] The term "acceptor material" in the present invention refers to an N-type organic semiconductor material.

[0011] The term "band gap" in the present invention refers to the optical band gap of a semiconductor material, and its value is obtained by dividing 1240 by the cut-off wavelength of the absorption edge of the semiconductor material.

[0012] The term "spectral response region" in the present invention refers to the effective working optical band of the photodiode and its array, and is defined as the wavelength range where the external quantum efficiency is greater than 10% of the peak efficiency.

[0013] The term "photosensitive layer" in the present invention refers to a thin film layer in a device structure that is responsible for absorbing photons and generating free electrons and holes.

[0014] The term "electron transport hole blocking layer" in the present invention refers to an N-type material layer that has the function of transporting electrons and blocking holes in the structure of an organic semiconductor device.

[0015] The term "hole transport electron blocking layer" in the present invention refers to a P-type material layer that has the function of transporting holes and blocking electrons in the structure of an organic semiconductor device.

[0016] The term "carrier mobility" in the present invention refers to a physical quantity used to describe the speed at which electrons or holes move inside an organic semiconductor material under the action of an electric field.

[0017] The term "lowest unoccupied molecular orbital" in the present invention refers to the molecular orbital with the lowest energy among the molecular orbitals that are not occupied by electrons in the organic semiconductor material, also known as LUMO.

[0018] The term "highest occupied molecular orbital" in the present invention refers to the molecular orbital with the highest energy among the molecular orbitals occupied by electrons in the organic semiconductor material, also known as HOMO.

[0019] The term "patterning process" in the present invention refers to a process of forming a pattern of a certain shape on a thin film layer of a certain material by means of a mask or photolithography.

[0020] An object of the present invention is to provide an organic photodiode with high sensitivity.

[0021] A highly sensitive organic photodiode comprising a photosensitive layer,

[0022] in

[0023] The photosensitive layer is a bulk heterojunction structure,

[0024] The photosensitive layer includes one or more donor materials and one or more acceptor materials;

[0025] The photosensitive layer

[0026] (i) comprising a donor material D1 and an acceptor material A1; and donor materials D2-Dn; and the energy gap of the donor materials D2-Dn is greater than the energy gap of the donor material D1 and / or the energy gap of the acceptor material A1;

[0027] or

[0028] (ii) comprising a donor material D1 and an acceptor material A1; and an acceptor material A2-An; and the energy gap of the acceptor material A2-An is greater than the energy gap of the donor material D1 and / or the energy gap of the acceptor material A1;

[0029] Among them, n≥2.

[0030] Furthermore, the photosensitive layer comprises

[0031] (i) a donor material D1 and an acceptor material A1; and a donor material D2; and the energy gap of the donor material D2 is larger than the energy gap of the donor material D1 and / or the energy gap of the acceptor material A1;

[0032] or

[0033] (ii) a donor material D1 and an acceptor material A1; and an acceptor material A2; and the energy gap of the acceptor material A2 is larger than the energy gap of the donor material D1 and / or the energy gap of the acceptor material A1.

[0034] Furthermore, the photosensitive layer comprises

[0035] A donor material D1 and an acceptor material A1; and an acceptor material A2; and the energy gap of the acceptor material A2 is larger than the energy gap of the donor material D1 and / or the energy gap of the acceptor material A1.

[0036] Furthermore, the photosensitive layer has an amorphous or nanocrystalline structure.

[0037] Furthermore, the thickness of the photosensitive layer is 100-500 nm.

[0038] Furthermore, the thickness of the photosensitive layer is 150-400 nm.

[0039] Furthermore, the highly sensitive organic photodiode is selected from a flip-chip structure or a face-up structure;

[0040] in,

[0041] The inverted structure includes, from bottom to top, a substrate, a cathode close to the substrate, an electron transport hole blocking layer, a photosensitive layer, a hole transport electron blocking layer, an anode close to the encapsulation layer, and an encapsulation layer;

[0042] The upright structure includes, from bottom to top, a substrate, an anode close to the substrate, a hole transport electron blocking layer, a photosensitive layer, an electron transport hole blocking layer, a cathode close to the encapsulation layer, and the encapsulation layer.

[0043] Further, the carrier mobility in the electron transport hole blocking layer is greater than the carrier mobility of the acceptor material in the photosensitive layer;

[0044] The carrier mobility in the hole transport electron blocking layer is greater than the carrier mobility of the donor material in the photosensitive layer.

[0045] Furthermore, the energy gaps of the materials in the electron transport hole blocking layer and the hole transport electron blocking layer are both larger than the energy gaps of the donor material and the acceptor material in the photosensitive layer.

[0046] Furthermore, the thickness of the electron transport hole blocking layer and the hole transport electron blocking layer are both smaller than the thickness of the photosensitive layer.

[0047] Furthermore, the effective Fermi levels of the electron transport hole blocking layer and the hole transport electron blocking layer correspond to the energy levels of the corresponding charges of the photosensitive layer; for the electron transport hole blocking layer, the energy level difference between the effective Fermi level of its electrons and the bottom of the conduction band of the photosensitive layer (called the lowest unoccupied molecular orbital in organic electronics) is greater than -0.15 eV; for the hole transport electron blocking layer, the energy level difference between the effective Fermi level of its holes and the top of the valence band of the photosensitive layer (called the highest occupied molecular orbital in organic electronics) is less than +0.15 eV. This is to meet the effective transmission of the corresponding charges under room temperature operation.

[0048] Furthermore, the surface defect state density of the electron transport hole blocking layer and the interface between the hole transport electron blocking layer and the photosensitive layer in the effective band gap of the photosensitive layer (between the HOMO of D1 and the LUMO of A1) is less than the bulk defect state density in the corresponding photosensitive layer.

[0049] Further, the material of the electron transport hole blocking layer is selected from organic compound 1, inorganic compound 1, or a combination thereof;

[0050] Wherein, the organic compound 1 is selected from fullerene and its derivatives, 4,7-diphenyl-1,10-phenanthroline, polyethyleneimine, polyethoxyethyleneimine, 2,9-dimethyl-4,7-biphenyl-1,10-phenanthroline, [9,9-dioctylfluorene-9,9-bis(N,N-dimethylaminopropyl)fluorene], bromo-[9,9-dioctylfluorene-9,9-bis(N,N-dimethylaminopropyl)fluorene], 8-hydroxyquinoline lithium, 1,3,5-tri(1-phenyl-1H-benzimidazol-2-yl)benzene, bis(2-methyl-8-quinolinol)-4-(phenylphenol)aluminum, 1,3,5-tri[(3-pyridyl)-phenyl-3-yl]benzene, or a mixture or a composite of the above materials;

[0051] The inorganic compound 1 is selected from zinc oxide, tin oxide, aluminum-doped zinc oxide, magnesium-doped zinc oxide, gallium-doped zinc oxide, titanium oxide, tantalum oxide, zinc sulfide, chromium sulfide, or a mixture or composite of the above materials.

[0052] Further, the material of the hole transport electron blocking layer is selected from organic compound 2, inorganic compound 2, or a combination thereof;

[0053] Wherein, the organic compound 2 is selected from one or more of 4,4'-cyclohexylbis[N,N'-bis(4-methylphenyl)aniline], N,N'-bis(naphthalene-1-yl)-N,N'-bis(phenyl)-benzidine, N,N'-bis(naphthalene-1-yl)-N,N'-bis(phenyl)-2,7-diamino-9,9-spirobifluorene, 2,2',7,7'-tetrakis[N,N-bis(4-methoxyphenyl)amino]-9,9'-spirobifluorene, 4,4',4"-tri(carbazole-9-yl)triphenylamine, poly(4-butyltriphenylamine), polyvinylcarbazole, polystyrene-N,N'-diphenyl-N,N'-bis-(3-methylphenyl)-(1,1)-biphenyl-4,4'-diamineperfluorocyclobutane, poly(3,4-ethylenedioxythiophene) mixed polystyrene sulfonate;

[0054] The inorganic compound 2 is selected from tungsten oxide, molybdenum oxide, vanadium oxide, chromium oxide, nickel oxide, copper oxide, cuprous oxide, cuprous thiocyanate, copper sulfide, copper iodide, or a mixture or a composite of the above materials.

[0055] Furthermore, the cathode has a transmittance greater than 20% in the spectral response region.

[0056] Furthermore, the anode has a transmittance greater than 20% in the spectral response region.

[0057] Furthermore, in the photosensitive layer, at least one of the donor material D1 and the acceptor material A1 has an energy gap of <1.77 eV;

[0058] And when the photosensitive layer exists

[0059] (i) when the donor material is D2-Dn, the absolute value of the energy difference between the highest occupied molecular orbital (HOMO) of the donor material Dm with the lowest energy gap and the highest occupied molecular orbital of the donor material D1 is ≤ 0.15 eV;

[0060] or

[0061] (ii) in the case of acceptor material A2-An, the absolute value of the energy difference between the lowest unoccupied molecular orbital (LUMO) of the lowest unoccupied molecular orbital of the acceptor material Am existing in the acceptor material A2-An and the lowest unoccupied molecular orbital of the acceptor material A1 is ≤0.15 eV.

[0062] Furthermore, when the photosensitive layer contains

[0063] (i) when the donor materials are D2-Dn, the donor material Dm with the lowest energy gap among the donor materials D2-Dn has an energy gap difference of >0.1 eV with the energy gap of the material with a lower energy gap in the donor material D1 or the acceptor material A1;

[0064] or

[0065] (ii) When the acceptor material is A2-An, the acceptor material Am with the lowest energy gap in the acceptor material A2-An has an energy gap difference of >0.1 eV with the energy gap of the material with a lower energy gap in the donor material D1 or the acceptor material A1.

[0066] Furthermore, in the photosensitive layer, the carrier mobility of the donor material D2 or the acceptor material A2 is greater than the carrier mobility of the donor material D1 and the acceptor material A1.

[0067] Further, the donor material D1 includes a conjugated polymer or small molecule based on the specific unit 1;

[0068] Wherein, the specific unit 1 is selected from one or more of the following structures:

[0069]

[0070] Wherein, the R1-R6 are independently selected from an alkyl group having 1 to 40 carbon atoms, or an alkyl derivative having 1 to 40 carbon atoms, including thiophene alkyl derivatives, phenyl alkyl derivatives, etc.;

[0071] One or more carbon atoms on the alkyl derivative are substituted by one or more of hydrogen atoms, oxygen atoms, alkenyl groups, alkynyl groups, aryl groups, hydroxyl groups, amino groups, carbonyl groups, carboxyl groups, ester groups, cyano groups, and nitro groups;

[0072] and / or,

[0073] One or more hydrogen atoms on the alkyl derivative are replaced by one or more of fluorine atoms, chlorine atoms, bromine atoms, and iodine atoms;

[0074] The X1 and X2 are independently selected from one or more of a hydrogen atom, a fluorine atom, a chlorine atom, a cyano group, and a nitro group.

[0075] Furthermore, the donor materials D2-Dn are independently selected from one or more of the following materials.

[0076]

[0077] Further, the receptor material A1 includes a conjugated polymer or small molecule based on the specific unit 2;

[0078] Wherein, the specific unit 2 is selected from one or more of the following structural units:

[0079]

[0080] Wherein, R1, R2, R3, R4, R5 and R6 are independently selected from an alkyl group having 1 to 40 carbon atoms, or an alkyl derivative having 1 to 40 carbon atoms, including thiophene alkyl derivatives, phenyl alkyl derivatives, etc.;

[0081] One or more carbon atoms on the alkyl derivative are substituted by one or more of hydrogen atoms, oxygen atoms, alkenyl groups, alkynyl groups, aryl groups, hydroxyl groups, amino groups, carbonyl groups, carboxyl groups, ester groups, cyano groups, and nitro groups;

[0082] and / or,

[0083] One or more hydrogen atoms on the alkyl derivative are replaced by one or more of fluorine atoms, chlorine atoms, bromine atoms, and iodine atoms;

[0084] The X1, X2, X3, X4, X5 and X6 are independently selected from one or more of a hydrogen atom, a fluorine atom, a chlorine atom, a cyano group and a nitro group.

[0085] Furthermore, the acceptor materials A2-An are independently selected from fullerene electron acceptor materials or non-fullerene electron acceptor materials.

[0086] Furthermore, the receptor materials A2-An are independently selected from one or more of the following materials:

[0087]

[0088]

[0089] Furthermore, the acceptor material A1 and the acceptor material A2 are independently selected from non-fullerene electron acceptor materials.

[0090] Further, the donor material D1, and the acceptor material A1 and the acceptor material A2 are respectively selected from one of the following groups: PTB7-Th, COTIC-4F and Y6; PTB7-Th, COTIC-4F and Y5; PTB7-Th, COTIC-4F and IT-4F; PTB7-Th, COTIC-4F and ITIC; PTB7: COTIC-4F and Y6; PTB7: COTIC-4F and Y5; PTB7: COTIC-4F and IT-4F; PTB7: COTIC-4F and ITIC; PTB7-Th, IEICO-4F and Y6; PTB7-Th, IEICO-4F and Y5; PTB7-Th, IEICO-4F and ITIC TB7-Th, IEICO-4F and IT-4F; PTB7-Th, IEICO-4F and ITIC; PTB7, IEICO-4F and Y6; PTB7, IEICO-4F and Y5; PTB7, IEICO-4F and IT-4F; PTB7, IEICO-4F and ITIC; PBDB-T, IEICO-4F and Y6; PBDB-T, IEICO-4F and Y5; PBDB-T, IEICO-4F and IT-4F; PBDB-T, IEICO-4F and ITIC; PTB7-Th, COi8DFIC and IT-4F; PTB7-Th, COi8DFIC and ITIC.

[0091] Furthermore, the mass ratio of the donor material D1, the acceptor material A1 and the acceptor material A2 is 1:(0.75-1.5):(0.0075-1.5), wherein the mass fraction of the acceptor material A2 in (acceptor material A1+acceptor material A2) is 1-50%.

[0092] Furthermore, the mass fraction of the acceptor material A2 in (acceptor material A1+acceptor material A2) is 5-40%.

[0093] Another object of the present invention is to provide an organic photodiode array, wherein the photosensitive pixels thereof include the above-mentioned highly sensitive organic photodiodes.

[0094] Furthermore, the substrate includes a pixel readout circuit composed of silicon-based complementary metal oxide semiconductor transistors or thin film transistors.

[0095] Furthermore, the pixel size is less than 50 μm.

[0096] Further, the organic photodiode array comprises the cathode close to the substrate or the anode close to the substrate, and a photosensitive layer;

[0097] in,

[0098] The size of the photosensitive pixel of the organic photodiode array is consistent with the cathode close to the substrate or the anode close to the substrate;

[0099] The cathode close to the substrate or the anode close to the substrate is patterned;

[0100] The photosensitive layer is not patterned.

[0101] Another object of the present invention is to provide a method for preparing the above-mentioned highly sensitive organic photodiode or the above-mentioned organic photodiode array, comprising the following steps:

[0102] (1) Substrate cleaning and readout circuit preparation;

[0103] (2) cathode film formation and photolithography patterning or anode film formation and photolithography patterning;

[0104] (3) Film formation of electron transport hole blocking layer or preparation of hole transport electron blocking layer;

[0105] (4) Preparation of photosensitive layer;

[0106] (5) Formation of hole transport electron blocking layer or preparation of electron transport hole blocking layer;

[0107] (6) Preparation of anode or cathode;

[0108] (7) Preparation of encapsulation layer.

[0109] Furthermore, the preparation of the photosensitive layer is selected from solution film formation or vacuum thermal evaporation deposition.

[0110] Furthermore, the preparation of the electron transport hole blocking layer and the hole transport electron blocking layer are independently selected from one or more of solution film formation, sol-gel film formation, vacuum thermal evaporation, atomic layer deposition, chemical vapor deposition, electrodeposition, and anodization.

[0111] Furthermore, the preparation of the cathode and the anode are independently selected from one or more of vacuum thermal evaporation, electron beam evaporation, molecular beam evaporation or plasma sputtering, atomic layer deposition or liquid film formation followed by reduction conversion, electroplating or electrodeposition.

[0112] Furthermore, the encapsulation layer is prepared by one of vacuum thermal evaporation, chemical vapor deposition, atomic layer deposition, plasma sputtering, and liquid film formation.

[0113] The present invention has the following beneficial effects:

[0114] (1) The organic photodiode disclosed in the present invention has a photosensitive layer of a multi-component blended bulk heterojunction structure, which is based on a donor material D1, an acceptor material A1, and contains other donor materials D2-Dn / other acceptor materials A2-An, and the energy gap of the donor materials D2-Dn / acceptor materials A2-An is limited to be greater than the energy gap of the donor material D1 and / or the energy gap of the acceptor material A1. It is surprisingly found that compared with the photosensitive layer of the bulk heterojunction structure of the two-component blend (containing only the donor material D1 and the acceptor material A1), the former has a more complementary absorption spectrum; and the introduction of other donor materials / other acceptor materials promotes the generation, transmission and extraction of charges in the photosensitive layer, thereby significantly improving the external quantum efficiency, spectral responsivity and light response speed of the organic photodiode in the long wavelength region (especially the infrared band greater than 700nm).

[0115] (2) Compared with the photosensitive layer of the bulk heterojunction structure of the two-component blend (containing only the donor material D1 and the acceptor material A1), in the photosensitive layer of the present invention, the addition of other donor materials / other acceptor materials forms a multi-component blended bulk heterojunction structure, and the neutralization effect makes the organic photodiode of the present invention have a lower doping concentration, a higher depletion layer width and a lower trap state density, so that the trap-assisted recombination inside the device is suppressed, the photosensitivity is improved, and the parallel resistance of the device is increased. These factors synergistically promote the reduction of dark current and noise spectral density, further improving the signal-to-noise ratio and specific detection rate of the device; in addition, the addition of other donor materials / other acceptor materials effectively suppresses the thermal noise, shot noise and 1 / f noise of the organic photodiode.

[0116] (3) As is known to all, as the energy gap decreases, thermal excitation of charges at room temperature becomes a factor that cannot be ignored. Inorganic single-crystal semiconductor devices used for short-wave infrared require an external refrigerator to achieve the specific detection rate required for practical applications. The high-sensitivity organic photodiode disclosed in the present invention has a reverse saturation dark current density of less than 10nA / cm at room temperature. 2 , can reach sub nA / cm at low bias 2 The device ideal factor is less than 1.6; the room temperature zero bias external quantum efficiency in the infrared region is higher than 50%, the room temperature external quantum efficiency under one volt bias is higher than 60%, and the room temperature specific detection rate is greater than 10 13 Jones. The above series of parameter results have reached or exceeded the room temperature performance of inorganic silicon single crystal, germanium single crystal and indium gallium arsenide single crystal photodetectors, and even reached their performance under refrigeration and low temperature. These amorphous or nanocrystalline thin-film organic photodiodes not only create conditions for various applications of artificial intelligence, but also provide new topics for material physics and device physics.

[0117] (4) The high-sensitivity organic photodiodes of the present invention can form an organic photodiode array, which can be directly integrated on the backplane of a TFT or CMOS by solution processing, and can be prepared into an image sensor array without patterning the photosensitive layer by photolithography or the like. The pixel of this diode array can be simply defined by the size and shape of the anode / cathode close to the substrate, that is, the size of the anode / cathode close to the substrate is consistent, and the etching of other layers between the anode / cathode close to the substrate and the anode / cathode close to the encapsulation layer is omitted. And this structure is essentially different from the image detector prepared by inorganic semiconductor wafers. Conventional forward-incident and back-incident CMOS and charge-coupled device (CCD) image sensor arrays require patterning between each pixel in the photosensitive layer to reduce signal crosstalk between pixels. These photolithography patterns involve deep groove etching and complex post-processing processes, which limit pixel spacing, process yield and device cost. When thin-film organic photodiodes are used as image sensor pixels, the crosstalk between pixels is greatly reduced due to the reduction in pixel thickness. Therefore, this organic photodiode array simplifies the structure and preparation process of the image sensor, enhances the responsiveness and response range and reduces the preparation cost, reduces the signal crosstalk between adjacent pixels, improves the sensitivity of the device to weak light, and improves the signal-to-noise ratio of the image sensor array. Preferably, when the photosensitive layer is amorphous or nanostructured, it fundamentally solves the stress problem in inorganic semiconductor single crystal devices, which is conducive to the preparation of low-cost, high-yield, high-stability photodetectors and image sensor arrays.

[0118] (5) It is worth mentioning that when the other donor materials / other acceptor materials added to the photosensitive layer are only acceptor materials, and the acceptor materials are non-fullerene structure acceptor materials, it is surprisingly found that the organic photodiode in the present invention has significant technical effects. Specifically, it has higher external quantum efficiency, lower dark current density, higher responsiveness and higher specific detection rate in the visible to infrared region, that is, it has higher sensitivity to weak light signals. Compared with fullerene structure acceptor materials, these non-fullerene structure acceptor materials have higher charge state density near the energy gap. This energy level structure leads to strong light absorption near the energy gap, and the light absorption coefficient is as high as 10 4 -10 5 cm -1 level. BRIEF DESCRIPTION OF THE DRAWINGS

[0119] Figure 1 A schematic diagram of the device structure of a highly sensitive organic photodiode in Example 1 of the present invention is shown.

[0120] Figure numerals: 1-substrate; 2-cathode or anode; 3-electron transport hole blocking layer or hole transport electron blocking layer; 4-photosensitive layer; 5-hole transport electron blocking layer or electron transport hole blocking layer; 6-anode or cathode; 7-encapsulation layer.

[0121] Figure 2 A schematic diagram showing the energy levels of the photosensitive layer in the highly sensitive organic photodiode in Example 1 is shown.

[0122] Figure 3 A cross-sectional view of the organic photodiode image array in Example 6-7 is shown.

[0123] Description of the drawings: 301 - pixel readout circuit; 302 - lower electrode (cathode or anode) array; 303 - electron transport hole blocking layer or hole transport electron blocking layer; 304 - photosensitive layer; 305 - hole transport electron blocking layer or electron transport hole blocking layer; 306 - upper electrode (anode or cathode) layer; 307 - encapsulation layer.

[0124] Figure 4 (a) shows the external quantum efficiency test graphs of Examples 1-3 and Comparative Example 1 in Test Example 1; Figure 4 (b) shows the external quantum efficiency test graph of Test Example 1, Examples 4-5 and Comparative Example 2.

[0125] Figure 5 (a) shows the response test graph of Examples 1-3 and Comparative Example 1 in Test Example 1; Figure 5 (b) shows the response test diagram of Examples 4-5 and Comparative Example 2 in Test Example 1.

[0126] Figure 6 (a) shows the specific detection rate test diagram of Examples 1-3 and Comparative Example 1 in Test Example 1; Figure 6 (b) shows the relative detection rate test diagram of Examples 4-5 and Comparative Example 2 in Test Example 1.

[0127] Figure 7 (a) shows the dark current test graph of Examples 1-3 and Comparative Example 1 in Test Example 1; Figure 7 (b) shows the dark current test graph of Test Example 1, Examples 4-5 and Comparative Example 2.

[0128] Figure 8 The noise spectral density test graphs of Examples 1-3 and Comparative Example 1 in Test Example 2 are shown.

[0129] Fig. 9 The capacitance test diagrams of Examples 1-3 and Comparative Example 1 in Test Example 2 are shown. DETAILED DESCRIPTION

[0130] In order to more clearly illustrate the technical solution of the present invention, the following examples are listed. Unless otherwise stated, the raw materials, reactions and post-treatment methods shown in the examples are common raw materials on the market and technical methods well known to those skilled in the art.

[0131] In an embodiment of the present invention, the substrate can be made of various insulating materials or high-resistance semiconductor materials, and it can have a flat surface or a curved surface of a specific shape. For an organic photodiode array used in an image sensor, the substrate is a readout circuit integrated with pixels. For a diode array with a high photosensitive pixel density, the substrate integrated with the pixel readout circuit is usually made on a single crystal silicon substrate using a CMOS process. For a diode array with a medium and low photosensitive pixel density, the substrate can be a readout circuit integrated with a thin film transistor on a glass, ceramic or plastic substrate. For image arrays of ultra-large scale and high photosensitive pixel density, the pixel readout circuit on the substrate can also be made of a hybrid circuit of CMOS and TFT.

[0132] Both the anode and cathode can be selected from a variety of materials. Among them:

[0133] For the bottom-incident organic photodiode and its array, the cathode / anode close to the substrate is transparent or partially transparent in the required wavelength range, and the optical transmittance of the electrode is higher than 20%. The cathode / anode close to the substrate can be a transparent metal oxide (such as indium tin oxide, zinc oxide and aluminum-doped zinc oxide, etc.), or a nitride (such as titanium nitride) and a nitride oxide of the corresponding metal. In addition, the anode / cathode close to the encapsulation layer can be a thicker metal material, which can be, but is not limited to, aluminum, silver, titanium, tantalum, molybdenum, copper, chromium, gold and nickel, etc.

[0134] For top-incident organic photodiodes and arrays thereof, the cathode / anode near the substrate can be used to reflect incident light in the required wavelength range to optimize the photosensitivity in a specific band, and the required conductivity and optical reflectivity can be obtained simultaneously by selecting a suitable metal material. In addition, the anode / cathode near the encapsulation layer is transparent or partially transparent in the required wavelength range, and the optical transmittance of the electrode is higher than 20%. In addition to thin metals and transparent metal oxides, the transparent or partially transparent anode / cathode near the encapsulation layer can be realized using nano-metal particles or nano-metal wire mesh.

[0135] For organic photodiodes and arrays of bidirectional incident structures, the anode / cathode layers close to the substrate and the encapsulation layer need to have high transmittance (higher than 20%) to the detection wavelength. It is worth noting that such organic thin film photodiodes and arrays can be prepared on substrates of various types, materials and shapes of confocal surfaces, and can be used for bidirectional light detection or omnidirectional three-dimensional detection.

[0136] Above the anode / cathode near the encapsulation layer is an encapsulation layer to ensure that the organic photodiode or photodiode array works stably under various usage environments and during the target life. If the organic photodiode or photodiode array is bottom-incident, this encapsulation layer does not need to be optically transparent. If the organic photodiode or photodiode array is top-incident, this encapsulation layer should be transparent in the working band and the optical transmittance should be above 50%.

[0137] This encapsulation layer can be formed by various vacuum coating methods, such as thermal evaporation, molecular beam coating or plasma sputtering, atomic layer deposition. It can also be prepared by liquid film forming methods, such as drop coating, dip coating, spin coating and various printing methods. In addition to selecting a single material, the encapsulation layer can also be formed by alternating multiple layers of film. In addition to improving the encapsulation performance, this alternating film structure can also be used to optimize the optical resonant cavity structure of the thin film photodiode in the working band, thereby optimizing its photosensitivity and specific detection rate.

[0138] Commonly used inorganic packaging materials include silicon oxide, silicon nitride, silicon oxynitride, aluminum oxide, zirconium oxide, magnesium oxide, zirconium oxide and magnesium fluoride. Commonly used organic packaging materials include polymethyl methacrylate, polyethylene oxide, polystyrene, polyvinyl pyrrolidone, polycarbonate, polyacrylic acid, epoxy resin, polyparaxylene and polysiloxazane.

[0139] The energy gaps of all donor materials and acceptor materials in the embodiments of the present invention are tested by ultraviolet-visible absorption spectroscopy. The specific method is to dissolve the donor material or the acceptor material in chloroform or chlorobenzene solvent, process the dissolved solution onto a quartz plate by spin coating, and use the obtained film for absorption spectrum testing. The optical energy gap is obtained by dividing 1240 by the absorption edge cutoff wavelength of the material.

[0140] The energy level of the lowest unoccupied molecular orbital and the energy level of the highest occupied molecular orbital of all donor materials and acceptor materials in the embodiments of the present invention are tested by cyclic voltammetry. Specifically, the oxidation and reduction potentials of the materials are measured by a three-electrode method, with Ag / Ag + As a reference electrode, anhydrous tetrabutylammonium hexafluorophosphate was used as the electrolyte.

[0141] The carrier mobility of all donor materials and acceptor materials in the embodiments of the present invention is tested by the space charge limited current method. The specific method is to prepare the corresponding single carrier device, and use a source meter to test the current-voltage characteristics of the device in the dark state, and obtain the carrier mobility by fitting the secondary region.

[0142] The light transmittance of the anode / cathode near the substrate and the anode / cathode near the encapsulation layer in the device light response region in the embodiment of the present invention is tested using a spectrometer. The specific method is to first prepare a metal film with the same thickness as the device electrode on a quartz wafer by vacuum thermal evaporation, and measure the transmission spectrum of the electrode.

[0143] Example 1

[0144] The device structure of the high-sensitivity organic photodiode in this embodiment is as follows: Figure 1 As shown, from bottom to top are glass substrate (2 mm), cathode (150 nm), electron transport hole blocking layer (30 nm), photosensitive layer (210 nm), hole transport electron blocking layer (12 nm), anode (150 nm) and encapsulation layer.

[0145] The cathode is made of indium tin oxide (ITO); the electron transport hole blocking layer is made of zinc oxide (the carrier mobility in this material is tested to be ~10 -1 cm 2 V -1 S -1 ); the hole transport electron blocking layer is molybdenum oxide (the carrier mobility in this material is tested to be ~10 -3 cm 2 V -1 S -1 ); the anode is metallic silver; and the encapsulation layer is epoxy resin.

[0146] The photosensitive layer adopts a ternary blended bulk heterojunction structure, which is a nanocrystalline structure. The donor material D1 is PTB7-Th, the acceptor material A1 is COTIC-4F, and the acceptor material A2 is Y6. The mass ratio of D1, A1 and A2 is 1:1.05:0.45.

[0147] The energy gap of donor material D1, PTB7-Th, is calculated to be 1.55 eV; the carrier mobility in this material is tested to be 2×10 -4 cm 2 V -1 S -1 ;

[0148] The energy gap of acceptor material A1, COTIC-4F, is calculated to be 1.10 eV; its LUMO energy level is -4.16 eV; and the carrier mobility in this material is tested to be 7×10 -5 cm 2 V -1 S -1 ;

[0149] The energy gap of the acceptor material A2, Y6, is calculated to be 1.33 eV; its LUMO energy level is -4.10 eV; the carrier mobility in this material is tested to be 5×10 -4 cm 2 V -1 S -1 .

[0150] The transmittance of the cathode of the high-sensitivity organic photodiode in the photosensitive layer is measured to be greater than 90%;

[0151] The transmittance of the anode of the high-sensitivity organic photodiode in the photosensitive layer is measured to be greater than 20%.

[0152] The method for preparing the above-mentioned highly sensitive organic photodiode comprises the following steps:

[0153] S1. The ITO conductive substrate was ultrasonically treated and cleaned with isopropyl alcohol, detergent, deionized water, and acetone in sequence, with each treatment lasting 20 minutes. The cleaned ITO conductive substrate was then placed in an oven at 60°C and dried for 5 hours; the ITO conductive substrate was then subjected to plasma surface treatment (vacuum degree: 2 mPa; duration: 20 seconds);

[0154] S2. Dissolve 0.4 g zinc acetate in a mixed solvent of 4 ml 2-methoxyethanol and 110 μl ethanolamine, and then heat and stir at 50°C for 10 h to obtain a sol-gel zinc oxide precursor solution. Spin-coat the solution at 3300 rpm for 30 s, and anneal on a hot plate at 150°C for 30 min to obtain a 30 nm thick zinc oxide film.

[0155] S3. PTB7-Th is selected as the donor material D1, COTIC-4F is selected as the acceptor material A1, and Y6 is selected as the acceptor material A2. The three are blended in the above mass ratio and added into a mixed solvent of chlorobenzene and 1-chloronaphthalene (98:2, v / v), so that the mass concentrations of PTB7-Th, COTIC-4F and Y6 are 10 mg / ml, 10.5 mg / ml and 4.5 mg / ml respectively. The mixture is stirred at 65°C for 3 hours, and then spin-coated onto the zinc oxide film at a speed of 700 rpm for 1 minute, and thermally annealed at 100°C for 10 minutes to finally obtain a photosensitive layer film of a specified thickness.

[0156] S4. The above structure is transferred to a thermal evaporation device at 5×10 -7 Under vacuum conditions of torr, a molybdenum oxide film of a specified thickness is formed. The photosensitive layer is deposited on the above-mentioned photosensitive layer film by thermal evaporation at a rate of.

[0157] S5. In 5×10 -7Under vacuum conditions of 0.1 torr, a silver film of a specified thickness was thermally evaporated on a molybdenum oxide film as an anode to obtain a highly sensitive organic photodiode.

[0158] Figure 1 A schematic diagram of the device structure of a highly sensitive organic photodiode in Example 1 of the present invention is shown. Figure 2 The energy level schematic diagram of the photosensitive layer in the highly sensitive organic photodiode in Example 1 is shown, from which the following conclusions can be drawn:

[0159] (1) The donor material D1, the acceptor material A1 and the acceptor material A2 form a gradient energy level arrangement, which is conducive to the dissociation of photogenerated excitons at the donor-acceptor interface and the transmission of free electrons and holes generated by the dissociation to the corresponding electrodes; (2) According to research, when the LUMO energy level difference between the acceptor material A2 and the acceptor material A1 is less than 0.15 eV, it is conducive to reducing non-radiative recombination losses, improving the open circuit voltage and built-in electric field of the device, and thus increasing the charge generation and transmission efficiency inside the device; Figure 2 The LUMO energy level difference between the acceptor material A2 and the acceptor material A1 is only 0.06 eV, which can effectively achieve the above purpose; (3) The acceptor material A2 has a larger optical energy gap than the acceptor material A1. The addition of the acceptor material A2 can increase the effective energy gap of the photosensitive layer and reduce the charge generation caused by the device through the thermal emission mechanism; on the other hand, it can increase the barrier for charge injection and reduce the charge injection under reverse bias, thereby reducing the dark current density; (4) The energy gaps of the electron transport hole blocking layer and the hole transport electron blocking layer are both higher than those of the donor material D1, the acceptor material A1 and the acceptor material A2, which is beneficial to increase the injection barrier between the electrode and reduce charge injection.

[0160] The electron transport hole blocking layer or the hole transport electron blocking layer can be selected from organic semiconductors, inorganic compound semiconductor materials or a combination thereof. Its function is to transport the corresponding charge to the corresponding electrode and block the opposite charge from reaching this electrode. The selection method includes: (a) the optical band gap of the electron transport hole blocking layer and the hole transport electron blocking layer is greater than the lowest optical band gap of the photosensitive layer, preferably greater than 0.3 eV; (b) Figure 2As shown, the effective Fermi levels of the electron transport hole blocking layer and the hole transport electron blocking layer correspond to the energy levels of the corresponding charges in the photosensitive layer; for the electron transport hole blocking layer, the energy difference between the effective Fermi level of its electrons and the LUMO (sometimes called the lowest unoccupied molecular orbital in organic electronics) of the photosensitive layer is greater than -0.15 eV; for the hole transport electron blocking layer, the energy difference between the effective Fermi level of its holes and the HOMO (sometimes called the highest occupied molecular orbital in organic electronics) of the photosensitive layer is less than +0.15 eV. This energy level difference condition satisfies the effective transmission of corresponding charges at room temperature; (c) the mobility or charge density of the corresponding charges transmitted by the electron transport hole blocking layer and the hole transport electron blocking layer is greater than the mobility of the corresponding charges in the photosensitive layer or the photoexcited charge density, so as to satisfy that the voltage drop on the photosensitive layer under working conditions is much greater than the voltage drop on the electron transport hole blocking layer or the hole transport electron blocking layer; (d) the surface defect state density at the interface between the electron transport hole blocking layer or the hole transport electron blocking layer and the photosensitive layer in the effective band gap of the photosensitive layer (between the HOMO of D1 and the LUMO of A1) is less than the body defect state density in the corresponding photosensitive layer.

[0161] Example 2

[0162] The device structure, materials used, and device preparation method in this embodiment are the same as those in Embodiment 1. The only difference is that the acceptor material A2 in Embodiment 1 is replaced by IT-4F, and the mass ratio of D1:A1:A2 is 1:1.2:0.3.

[0163] The energy gap of acceptor material A2, IT-4F, is calculated to be 1.48 eV; its LUMO energy level is -4.14 eV; and the carrier mobility in this material is tested to be 3×10 -4 cm 2 V -1 S -1 .

[0164] Other parameters of the same materials used are the same as those in Example 1.

[0165] Example 3

[0166] The device structure, materials used, and device preparation method in this embodiment are the same as those in Example 1. The only difference is that the acceptor material A2 in Example 1 is replaced by PC 71 BM, and the mass ratio of D1:A1:A2 is 1:1.2:0.3.

[0167] Acceptor material A2, PC 71 The energy gap of BM is calculated to be 2.13 eV; its LUMO energy level is -4.20 eV; and the carrier mobility in this material is tested to be 6×10 -4 cm 2V -1 S -1 ;

[0168] Other parameters of the same materials used are the same as those in Example 1.

[0169] Example 4

[0170] The device structure, materials used, and device preparation method in this embodiment are the same as those in Example 1. The only difference is that the preparation method S3 in Example 1 is replaced by the following processing conditions:

[0171] S3: PTB7-Th as donor material D1, COi8DFIC as acceptor material A1, and IT-4F as acceptor material A2 were blended in a mass ratio of 1:1.25:0.25, and added into a mixed solvent of chlorobenzene and 1,8-diiodooctane (99:1, v / v), so that the mass concentrations of PTB7-Th, COi8DFIC, and IT-4F were 10 mg / ml, 12.5 mg / ml, and 2.5 mg / ml, respectively. The mixture was heated and stirred at 70°C for 5 hours, and then the solution was spin-coated onto a zinc oxide film at a speed of 1000 rpm for 1 minute, and thermally annealed at 120°C for 10 minutes, and finally a photosensitive layer film of a specified thickness was obtained.

[0172] The energy gap of the acceptor material A1, COi8DFIC, is calculated to be 1.31 eV; its LUMO energy level is -4.09 eV; the carrier mobility of this material is tested to be 1×10 -4 cm 2 V -1 S -1 .

[0173] Other parameters of the same materials used are the same as those in Example 1.

[0174] Example 5

[0175] The device structure, materials used, and device preparation method in this embodiment are the same as those in embodiment 4. The only difference is that the acceptor material A2 in embodiment 4 is replaced by PC 71 BM.

[0176] Other parameters of the same materials used are the same as those in Example 4.

[0177] Example 6

[0178] This embodiment provides an organic photodiode array composed of the high-sensitivity organic photodiodes in the above embodiment 1. The device structure of the organic photodiode array is as follows: Figure 3As shown in the figure, the organic photodiode array includes, from bottom to top, a pixel readout circuit 301 made of silicon-based complementary metal oxide semiconductor transistors (MOSFET) on a single crystal silicon substrate, and each pixel readout circuit is connected to a cathode array 302 that defines the pixel size. Above the cathode array are an electron transport hole blocking layer 303, a photosensitive layer 304, a hole transport electron blocking layer 305, an anode layer 306, and an encapsulation layer 307. From 303 to 307, they are all continuous structures in the entire array area, and no patterning between pixels is required.

[0179] Among them, the cathode array is an aluminum, titanium or titanium-aluminum alloy electrode with a thickness of 100nm, the electron transport hole blocking layer is a zinc oxide film (30nm), the material composition of the photosensitive layer refers to the material of the photosensitive layer of Example 1, the hole transport electron blocking layer is a molybdenum oxide film (10nm), the anode layer is a stacked structure of a silver electrode (10nm) and a molybdenum oxide film (50nm), and the encapsulation layer is an epoxy resin.

[0180] The transmittance of the anode of the high-sensitivity organic photodiode array in the range of 300-1100 nm is measured to be greater than 60%.

[0181] The array has a pixel size of 25 μm and a pixel number of 1×256 or 1×512, and imaging tests have been performed on it. Figure 3 The organic photodiode array shown, in which the pixels are defined only by the bottom electrode, can be used for digital camera applications with high pixel density.

[0182] The method for preparing the above-mentioned highly sensitive organic photodiode array comprises the following steps:

[0183] S1. The pixel readout circuit composed of silicon-based complementary metal oxide semiconductor transistors was transferred to the evaporation glove box. -7 Under vacuum conditions of torr, an aluminum metal electrode array of a specified thickness is deposited by thermal evaporation;

[0184] S2-S4. The preparation method of the zinc oxide film, the photosensitive layer film and the molybdenum oxide film is the same as that in Example 1.

[0185] S5. In 5×10 -7 Under vacuum conditions of 0.1 torr, a silver film of specified thickness is thermally evaporated on the molybdenum oxide film. After evaporating the silver electrode, wait for 5 to 10 minutes, and then evaporate another layer of molybdenum oxide film of specified thickness as an optical adjustment layer. The anode of this stacked structure can increase the transmittance of the electrode in the infrared region, thereby obtaining a highly sensitive organic photodiode array.

[0186] Example 7

[0187] The device structure, materials used, and device fabrication method in this embodiment are the same as those in Embodiment 6. The only difference is that the pixel readout circuit 301 in Embodiment 6 is replaced by a pixel readout circuit composed of thin-film transistors (TFTs) on a glass substrate.

[0188] Comparative Example 1

[0189] The device structure, materials used, and device fabrication method in this embodiment are the same as those in Embodiment 1. The only difference is that the photosensitive layer in Comparative Example 1 is a binary blend bulk heterojunction structure, which includes a donor material D1 of PTB7-Th and an acceptor material A1 of COTIC-4F, and the mass ratio of the donor material D1 to the acceptor material A1 is 1:1.5.

[0190] Comparative Example 2

[0191] The device structure, materials used, and device fabrication method in this embodiment are the same as those in Embodiment 4. The only difference is that the photosensitive layer in Comparative Example 2 is a binary blend bulk heterojunction structure, which includes a donor material D1 of PTB7-Th and an acceptor material A1 of COi8DFIC, and the mass ratio of the donor material D1 to the acceptor material A1 is 1:1.

[0192] Test Example 1

[0193] In order to test the technical effects of the photosensitive layers in the above embodiments and comparative examples on organic photodiodes, the following tests were carried out.

[0194] The volt-ampere characteristics of the organic photodiodes in the embodiments and comparative examples can be described by an ideal p-n junction or p-i-n junction under a forward bias of 0 < V < 0.5V, and the current density and forward bias follow an exponential relationship. Under a forward bias exceeding 0.6V, the J-V is limited by space charge limited transport and ultimately limited by the series resistance of the diode. The volt-ampere characteristic nodes in the dark state within the entire measurement range can be described by the following Shockley equation:

[0195]

[0196] where J0 is the saturation dark current density, n is the ideality factor, k is the Boltzmann constant, T is the temperature, and R sh is the parallel resistance.

[0197] EQE and responsivity tests: These were carried out using the method in the literature (DOI: 10.1063 / 5.0018274). The obtained results are respectively as Figure 4 (a), Figure 4 (b), Figure 5 (a) and Figure 5(b) As shown. It can be clearly seen from the figure that compared with the binary blended photosensitive layer structure in Comparative Examples 1 and 2, the ternary blended photosensitive layer structure with the addition of acceptor material A2, i.e., Examples 1-5, shows stronger external quantum efficiency and responsivity in the full band range from visible to infrared. This is because: on the one hand, the addition of acceptor material A2 increases the grain correlation length of the molecular stacking of the blended film and improves the crystallinity; on the other hand, the electron mobility of acceptor material A2 itself is higher than that of acceptor material A1, so the addition of acceptor material A2 can improve the charge transport and extraction in the photosensitive layer, thereby enhancing EQE and responsivity.

[0198] It is worth mentioning that, compared with the device in which the acceptor material A2 is fullerene (i.e., Example 3 and Example 5), the device in which the acceptor material A2 is non-fullerene (i.e., Example 1, Example 2, and Example 4) respectively exhibits more ideal EQE and responsivity. This is because: (1) Compared with the fullerene acceptor material A2, the photoluminescence spectrum of the non-fullerene acceptor material A2 can overlap with the absorption spectrum of the acceptor material A1, that is, there is a Förster energy transfer between the non-fullerene acceptor material A2 and the acceptor material A1, which reduces the non-radiative recombination and provides an additional dissociation interface for the photogenerated excitons, thereby enhancing the EQE response of the device; (2) Compared with the fullerene acceptor material A2, the non-fullerene acceptor material A2 and the acceptor material A1 are more likely to form an acceptor alloy phase due to their similar structures, which is conducive to the formation of appropriate phase separation and promotes the dissociation of excitons and the transfer of charges; (3) Such non-fullerene electron acceptor material A2 has a direct energy gap and has a stronger electronic state density near the energy gap. (4) The non-fullerene acceptor material A2 has a higher absorption coefficient in the visible to infrared region, which can enhance the device’s ability to capture infrared light.

[0199] Detection rate test: The method in the literature (DOI: 10.1063 / 5.0018274) was used. The results are as follows Figure 6 (a) and Figure 6(b) As shown in the figure. It can be clearly seen that compared with Comparative Examples 1 and 2, the addition of acceptor material A2 has increased the specific detection rate of the device by more than one order of magnitude (see Examples 1-3 and Examples 4-5), and thus the sensitivity of the device to the optical signal has also been greatly improved. In particular, the specific detection rates of Examples 1-2 and Example 4 are significantly improved compared with the corresponding specific detection rates of Examples 3 and 5, which shows that compared with the fullerene acceptor material A2, the non-fullerene acceptor material A2 has a more obvious effect on improving the specific detection rate of the device, which is due to: (1) Compared with the fullerene acceptor material A2, the non-fullerene acceptor material A2 can significantly improve the spectral responsivity of the device; (2) Compared with the fullerene acceptor material A2, the non-fullerene acceptor material A2 can more significantly reduce the dark current density of the device, improve the signal-to-noise ratio of the device and the rectification ratio of the diode.

[0200] Dark current test: The method in the literature (DOI:10.1063 / 5.0018274) was used. The results are as follows Figure 7 (a) and Figure 7 (b) As shown in the figure. It can be clearly seen from the figure that compared with comparative examples 1-2, the dark current density of Examples 1-5 under reverse bias is reduced by 1 to 2 orders of magnitude, and the dark current density of Examples 3 and 5 is higher than the dark current density of the corresponding Examples 1-2 and 4. This shows that the non-fullerene acceptor material A2 can more significantly reduce the dark current of the organic photodiode. This is because compared with the fullerene acceptor material A2, the non-fullerene acceptor material A2 has a more regular planar structure, and the defect state density caused by its energy disorder or structural disorder is often lower, and the lower defect state density can reduce the trap-assisted recombination of the device in the dark state and reduce the generation of recombination current.

[0201] Through the above Shockley equation, we tested and fitted the dark current characteristics of different embodiments, and the results of the corresponding parameters are shown in Table 1.

[0202] Table 1 Results of relevant parameters of organic photodiodes of Examples 1-5 and Comparative Examples 1-2

[0203]

[0204]

[0205] Note: The responsivity and specific detectivity in Comparative Example 1 and Examples 1-3 are taken from the values ​​at a wavelength of 1050 nm in the corresponding responsivity spectra and specific detectivity spectra, while the responsivity and specific detectivity in Comparative Example 2 and Examples 4-5 are taken from the values ​​at a wavelength of 940 nm.

[0206] The test results show that compared with the two-component organic photodiode of Comparative Example 1-2, the reverse saturation dark current density of the devices of Examples 1-3 and Examples 4-5 is suppressed, and the value is less than 2nA / cm 2 , the parallel resistance is increased by about one order of magnitude, and the ideal factors of Examples 1-3 are all less than 1.6. The decrease in reverse saturation dark current density indicates that the addition of acceptor material A2 reduces the theoretical minimum dark current density of the device, while the increase in parallel resistance indicates that the addition of acceptor material A2 can reduce charge injection under reverse bias, which is consistent with the reduction in dark current. In addition, the organic photodiode in Example 1 exhibits the highest responsivity (0.45 A / W) and specific detectivity (3.4×10 13 Jones), which is higher than the responsivity (0.23 A / W) and specific detectivity (9.0×10 12 Jones). Similarly, the specific detection rates of Example 2 and Example 4 are also higher than those of the corresponding Example 3 and Example 5, which is due to the fact that the non-fullerene acceptor material A2 has a more obvious inhibitory effect on the reverse saturation dark current of the device, and at the same time has a greater improvement in the responsiveness and parallel resistance of the device.

[0207] Test Example 2

[0208] In order to further understand the deep-seated mechanism of the reduction of dark current density in Examples 1-3 relative to Comparative Example 1, the following test was performed.

[0209] Noise spectral density test: The method in the literature (DOI:10.1063 / 5.0018274) was used. The results are as follows Figure 8As shown. It is generally believed that the dark state noise of organic photodiodes includes thermal noise, shot noise and 1 / f noise, among which thermal noise and shot noise are frequency-independent, and the two are collectively referred to as white noise, while 1 / f noise is inversely proportional to frequency, so it is also called low-frequency noise. At present, there is still controversy in academia about the generation mechanism and influencing factors of 1 / f noise. Therefore, the noise spectrum test is very helpful for analyzing the 1 / f noise and total noise of the device. It can be clearly seen from the figure that the device noise of comparative example 1 has a very obvious frequency dependence in the low-frequency range, indicating that when the device with a two-component photosensitive layer works in the low-frequency band, its 1 / f noise will dominate, and in the range of 10-25Hz, the noise of comparative example 1 changes less with frequency, and its total noise is mainly composed of thermal noise and shot noise. In contrast, the noise of the devices of Examples 1-3 in the low-frequency range does not have frequency dependence. In addition, in the range of 10-25Hz, the noise spectrum density of Examples 1-3 is lower than the noise spectrum density of Comparative Example 1. This shows that the total noise of the device of Examples 1-3 is only composed of thermal noise and shot noise. The above analysis further illustrates that the addition of acceptor material A2 not only reduces the amplitude of noise (including thermal noise and shot noise), but also effectively eliminates the 1 / f noise in the low-frequency region. The simultaneous suppression of these three parts of noise promotes the reduction of the dark current of the device and the improvement of the specific detection rate, that is, the sensitivity of the device to weak light is improved.

[0210] In addition, compared with Example 3, the noise spectral density of the devices in Example 1 and Example 2 in the low-frequency range is lower, which indicates that compared with the fullerene acceptor material A2, the addition of the non-fullerene acceptor material A2 can more effectively reduce the 1 / f noise of the device, which is consistent with the trend of reducing the dark current.

[0211] Capacitance test: The method in the literature (DOI:10.1063 / 5.0018274) was used. The results are as follows Fig. 9 As shown. It can be clearly seen from the figure that compared with the device of comparative example 1, the devices of Examples 1-3 all show a larger slope in the linear region at 0-0.4V, which means that the addition of acceptor material A2 reduces the doping concentration of the photosensitive layer and increases the depletion layer width of the device, which synergistically leads to a reduction in dark current. It is worth mentioning that the device of Example 1 has a larger slope than the device of Example 3, which means that compared with the fullerene acceptor material A2, the non-fullerene acceptor material A2 can further reduce the doping concentration of the device and increase the depletion layer width. Fig. 9 The test results show that the total effective defect state density of the bulk defect state in the photosensitive layer and the surface defect state at the interface between the electron blocking layer and the hole blocking layer is less than 1×10 15 cm -3 .

[0212] The measurement results of the above device volt-ampere characteristics and capacitance prove that the addition of the third component in the photosensitive layer effectively reduces the impurity defect state density within the bulk heterojunction energy gap, suppresses the trap-assisted recombination channel of photogenerated charges, enhances the external quantum efficiency, reduces the dark current, and thereby improves the device's specific detectivity.

[0213] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above and that the present invention can be implemented in other specific forms without departing from the spirit or essential features of the present invention. Therefore, the embodiments should be considered exemplary and non-restrictive in all respects, and the scope of the present invention is defined by the appended claims rather than the above description, and it is intended that all changes falling within the meaning and scope of the equivalent elements of the claims be included in the present invention.

[0214] In addition, it should be understood that although the present specification is described according to implementation modes, not every implementation mode contains only one independent technical solution. This description of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment may also be appropriately combined to form other implementation modes that can be understood by those skilled in the art.

Claims

1. A highly sensitive organic photodiode, characterized in that: The highly sensitive organic photodiode comprises a photosensitive layer, in The photosensitive layer is a bulk heterojunction structure, The photosensitive layer includes one or more donor materials and one or more acceptor materials; The photosensitive layer (i) comprising a donor material D1 and an acceptor material A1; and donor materials D2-Dn; and the energy gap of the donor materials D2-Dn is greater than the energy gap of the donor material D1 and / or the energy gap of the acceptor material A1; or (ii) comprising a donor material D1 and an acceptor material A1; and an acceptor material A2-An; and the energy gap of the acceptor material A2-An is greater than the energy gap of the donor material D1 and / or the energy gap of the acceptor material A1; Where n≥2; In the photosensitive layer, at least one of the donor material D1 and the acceptor material A1 has an energy gap of less than 1.77 eV; And when the photosensitive layer exists (i) when the donor material is D2-Dn, the absolute value of the energy difference between the highest occupied molecular orbital of the donor material Dm with the lowest energy gap and the highest occupied molecular orbital of the donor material D1 is ≤ 0.15 eV; or (ii) in the case of acceptor material A2-An, the absolute value of the energy difference between the lowest unoccupied molecular orbital of the acceptor material Am with the lowest energy gap and the lowest unoccupied molecular orbital of the acceptor material A1 is ≤0.15 eV.

2. The highly sensitive organic photodiode according to claim 1, characterized in that: The photosensitive layer includes (i) a donor material D1 and an acceptor material A1; and a donor material D2; and the energy gap of the donor material D2 is greater than the energy gap of the donor material D1 and / or the energy gap of the acceptor material A1; or (ii) a donor material D1 and an acceptor material A1; and an acceptor material A2; and the energy gap of the acceptor material A2 is larger than the energy gap of the donor material D1 and / or the energy gap of the acceptor material A1.

3. The highly sensitive organic photodiode according to claim 2, characterized in that: The photosensitive layer includes A donor material D1 and an acceptor material A1; and an acceptor material A2; and the energy gap of the acceptor material A2 is larger than the energy gap of the donor material D1 and / or the energy gap of the acceptor material A1.

4. The highly sensitive organic photodiode according to claim 3, characterized in that: The photosensitive layer has an amorphous or nanocrystalline structure.

5. The highly sensitive organic photodiode according to claim 3, characterized in that: The thickness of the photosensitive layer is 100-500 nm.

6. The highly sensitive organic photodiode according to claim 5, characterized in that: The thickness of the photosensitive layer is 150-400 nm.

7. The highly sensitive organic photodiode according to claim 1, characterized in that: The highly sensitive organic photodiode is selected from a flip-chip structure or a face-up structure; in, The inverted structure includes, from bottom to top, a substrate, a cathode close to the substrate, an electron transport hole blocking layer, a photosensitive layer, a hole transport electron blocking layer, an anode close to the encapsulation layer, and an encapsulation layer; The upright structure includes, from bottom to top, a substrate, an anode close to the substrate, a hole transport electron blocking layer, a photosensitive layer, an electron transport hole blocking layer, a cathode close to the encapsulation layer, and the encapsulation layer.

8. The highly sensitive organic photodiode according to claim 7, characterized in that: The carrier mobility in the electron transport hole blocking layer is greater than the carrier mobility of the acceptor material in the photosensitive layer; The carrier mobility in the hole transport electron blocking layer is greater than the carrier mobility of the donor material in the photosensitive layer.

9. The highly sensitive organic photodiode according to claim 7, characterized in that: The energy gaps of the materials in the electron transport hole blocking layer and the hole transport electron blocking layer are both greater than the energy gaps of the donor material and the acceptor material in the photosensitive layer.

10. The highly sensitive organic photodiode according to claim 9, characterized in that: The thickness of the electron transport hole blocking layer and the hole transport electron blocking layer are both smaller than the thickness of the photosensitive layer.

11. The highly sensitive organic photodiode according to claim 7, characterized in that: The material of the electron transport hole blocking layer is selected from organic compound 1, inorganic compound 1, or a combination thereof; Wherein, the organic compound 1 is selected from fullerene and its derivatives, 4,7-diphenyl-1,10-phenanthroline, polyethyleneimine, polyethoxyethyleneimine, 2,9-dimethyl-4,7-biphenyl-1,10-phenanthroline, [9,9-dioctylfluorene-9,9-bis(N,N-dimethylaminopropyl)fluorene], bromo-[9,9-dioctylfluorene-9,9-bis(N,N-dimethylaminopropyl)fluorene], 8-hydroxyquinoline lithium, 1,3,5-tri(1-phenyl-1H-benzimidazol-2-yl)benzene, bis(2-methyl-8-quinolinol)-4-(phenylphenol)aluminum, 1,3,5-tri[(3-pyridyl)-phenyl-3-yl]benzene, or a mixture or a composite of the above materials; The inorganic compound 1 is selected from zinc oxide, tin oxide, aluminum-doped zinc oxide, magnesium-doped zinc oxide, gallium-doped zinc oxide, titanium oxide, tantalum oxide, zinc sulfide, chromium sulfide, or a mixture or composite of the above materials.

12. The highly sensitive organic photodiode according to claim 7, characterized in that: The material of the hole transport electron blocking layer is selected from organic compound 2, inorganic compound 2, or a combination thereof; Wherein, the organic compound 2 is selected from one or more of 4,4'-cyclohexylbis[N,N'-bis(4-methylphenyl)aniline], N,N'-bis(naphthalene-1-yl)-N,N'-bis(phenyl)-benzidine, N,N'-bis(naphthalene-1-yl)-N,N'-bis(phenyl)-2,7-diamino-9,9-spirobifluorene, 2,2',7,7'-tetrakis[N,N-bis(4-methoxyphenyl)amino]-9,9'-spirobifluorene, 4,4',4"-tri(carbazole-9-yl)triphenylamine, poly(4-butyltriphenylamine), polyvinylcarbazole, polystyrene-N,N'-diphenyl-N,N'-bis-(3-methylphenyl)-(1,1)-biphenyl-4,4'-diamineperfluorocyclobutane, poly(3,4-ethylenedioxythiophene) mixed polystyrene sulfonate; The inorganic compound 2 is selected from tungsten oxide, molybdenum oxide, vanadium oxide, chromium oxide, nickel oxide, copper oxide, cuprous oxide, cuprous thiocyanate, copper sulfide, copper iodide, or a mixture or a composite of the above materials.

13. The highly sensitive organic photodiode according to claim 7, characterized in that: The cathode has a transmittance greater than 20% in the spectral response region.

14. The highly sensitive organic photodiode according to claim 7, characterized in that: The anode has a transmittance greater than 20% in the spectral response region.

15. The highly sensitive organic photodiode according to claim 1, characterized in that: When the photosensitive layer contains (i) when the donor materials are D2-Dn, the donor material Dm with the lowest energy gap among the donor materials D2-Dn has an energy gap difference of >0.1 eV with the energy gap of the material with a lower energy gap in the donor material D1 or the acceptor material A1; or (ii) When the acceptor material is A2-An, the acceptor material Am with the lowest energy gap in the acceptor material A2-An has an energy gap difference of >0.1 eV with the energy gap of the material with a lower energy gap in the donor material D1 or the acceptor material A1.

16. The highly sensitive organic photodiode according to claim 7, characterized in that: In the photosensitive layer, the carrier mobility of the donor material D2 or the acceptor material A2 is greater than the carrier mobility of the donor material D1 and the acceptor material A1.

17. The highly sensitive organic photodiode according to claim 7, characterized in that: The donor material D1 includes a conjugated polymer or small molecule based on a specific unit 1; Wherein, the specific unit 1 is selected from one or more of the following structures: Wherein, said R1-R6 are independently selected from alkyl groups having 1 to 40 carbon atoms; The X1 and X2 are independently selected from one or more of a hydrogen atom, a fluorine atom, a chlorine atom, a cyano group, and a nitro group.

18. The highly sensitive organic photodiode according to claim 7, characterized in that: The donor materials D2-Dn are independently selected from one or more of the following materials:

19. The highly sensitive organic photodiode according to claim 7, characterized in that: The receptor material A1 includes a conjugated polymer or small molecule based on a specific unit 2; Wherein, the specific unit 2 is selected from one or more of the following structural units: Wherein, R1, R2, R3, R4, R5 and R6 are independently selected from alkyl groups having 1 to 40 carbon atoms; The X1, X2, X3, X4, X5 and X6 are independently selected from one or more of a hydrogen atom, a fluorine atom, a chlorine atom, a cyano group and a nitro group.

20. The highly sensitive organic photodiode according to claim 7, characterized in that: The acceptor materials A2-An are independently selected from fullerene electron acceptor materials or non-fullerene electron acceptor materials.

21. The highly sensitive organic photodiode according to claim 20, characterized in that: The receptor materials A2-An are independently selected from one or more of the following structural formulas:

22. The highly sensitive organic photodiode according to claim 7, characterized in that: The acceptor material A1 and the acceptor material A2 are independently selected from non-fullerene electron acceptor materials.

23. The highly sensitive organic photodiode according to claim 22, characterized in that: The donor material D1, and the acceptor material A1 and the acceptor material A2 are selected from one of the following groups: PTB7-Th, COTIC-4F and Y6; PTB7-Th, COTIC-4F and Y5; PTB7-Th, COTIC-4F and IT-4F; PTB7-Th, COTIC-4F and ITIC; PTB7: COTIC-4F and Y6; PTB7: COTIC-4F and Y5; PTB7: COTIC-4F and IT-4F; PTB7: COTIC-4F and ITIC; PTB7-Th, IEICO-4F and Y6; PTB7-Th, IEICO-4F and Y5; PTB7 -Th, IEICO-4F and IT-4F; PTB7-Th, IEICO-4F and ITIC; PTB7, IEICO-4F and Y6; PTB7, IEICO-4F and Y5; PTB7, IEICO-4F and IT-4F; PTB7, IEICO-4F and ITIC; PBDB-T, IEICO-4F and Y6; PBDB-T, IEICO-4F and Y5; PBDB-T, IEICO-4F and IT-4F; PBDB-T, IEICO-4F and ITIC; PTB7-Th, COi8DFIC and IT-4F; PTB7-Th, COi8DFIC and ITIC.

24. The highly sensitive organic photodiode according to claim 23, characterized in that: The mass ratio of the donor material D1, the acceptor material A1 and the acceptor material A2 is 1:(0.75-1.5):(0.0075-1.5), wherein the mass fraction of the acceptor material A2 in (acceptor material A1+acceptor material A2) is 1-50%.

25. The highly sensitive organic photodiode according to claim 23, characterized in that: The mass fraction of the acceptor material A2 in (acceptor material A1+acceptor material A2) is 5-40%.

26. An organic photodiode array, characterized in that: The photosensitive picture element of the high-sensitivity organic photodiode array comprises the high-sensitivity organic photodiode according to any one of claims 7-25.

27. The organic photodiode array according to claim 26, characterized in that: The substrate includes a pixel readout circuit composed of a silicon-based complementary metal oxide semiconductor transistor or a thin film transistor.

28. The organic photodiode array according to claim 26, characterized in that: The photosensitive pixel comprises a highly sensitive organic photodiode according to claim 26; The pixel size is less than 50 μm.

29. The organic photodiode array according to claim 28, characterized in that: The organic photodiode array comprises the cathode close to the substrate or the anode close to the substrate, and a photosensitive layer; in, The size of the photosensitive pixel of the organic photodiode array is consistent with the cathode close to the substrate or the anode close to the substrate; The cathode close to the substrate or the anode close to the substrate is patterned; The photosensitive layer is not patterned.

30. A method for preparing a highly sensitive organic photodiode according to any one of claims 7 to 25 or an organic photodiode array according to claim 27, characterized in that: The following steps are involved: (1) Substrate cleaning and readout circuit preparation; (2) cathode film formation and photolithography patterning or anode film formation and photolithography patterning; (3) Film formation of electron transport hole blocking layer or preparation of hole transport electron blocking layer; (4) Preparation of photosensitive layer; (5) Formation of hole transport electron blocking layer or preparation of electron transport hole blocking layer; (6) Preparation of anode or cathode; (7) Preparation of encapsulation layer.

31. The method for preparing a highly sensitive organic photodiode or an organic photodiode array according to claim 30, characterized in that: The photosensitive layer is prepared by a method selected from solution film formation or vacuum thermal evaporation deposition.

32. The method for preparing a highly sensitive organic photodiode or an organic photodiode array according to claim 30, characterized in that: The preparation of the electron transport hole blocking layer and the hole transport electron blocking layer are independently selected from one or more of solution film formation, sol-gel film formation, vacuum thermal evaporation, atomic layer deposition, chemical vapor deposition, electrodeposition, and anodization.

33. The method for preparing a highly sensitive organic photodiode or an organic photodiode array according to claim 30, characterized in that: The cathode and the anode are prepared independently by one or more methods selected from vacuum thermal evaporation, electron beam evaporation, molecular beam evaporation or plasma sputtering, atomic layer deposition or liquid film formation followed by reduction conversion, electroplating or electrodeposition.

34. The method for preparing a highly sensitive organic photodiode or an organic photodiode array according to claim 30, characterized in that: The encapsulation layer is prepared by vacuum thermal evaporation, chemical vapor deposition, atomic layer deposition, plasma sputtering, and liquid film formation.

Images