A multiplication-type organic photodetector based on high-temperature induced interface traps

Abstract

The present invention belongs to the field of organic semiconductor technology, and specifically provides a multiplication-type organic photodetector based on high-temperature induced interface traps, which is used to solve the problems of low response speed, high operating voltage and complex process of existing multiplication-type organic photodetectors. The present invention comprises: a substrate, a transparent conductive cathode, a cathode modification layer, a photosensitive layer, an anode modification layer and an anode layer stacked in sequence from bottom to top; wherein the photosensitive layer is subjected to high-temperature thermal annealing treatment, so that a granular defect morphology is formed on its upper surface as an interface trap, so that photogenerated carriers are trapped and accumulated at the interface, thereby inducing interface energy band bending and tunneling injection of external circuit charges, generating a photomultiplier effect, and thus significantly improving the external quantum efficiency of the device and enhancing the detection performance of the detector; and the defect state morphology can be finely controlled by the thermal annealing temperature, annealing time and thickness of the photosensitive layer; in addition, the preparation process of the present invention is simple, the cost is low, and it is easy to realize industrial production.

Description

Technical Field

[0001] The present invention belongs to the technical field of organic semiconductors, relates to an amplified organic photodetector, and specifically provides an amplified organic photodetector based on high-temperature induced interface traps. Background Art

[0002] In recent years, organic photodetectors have attracted considerable research attention due to their advantageous properties, including tunable response spectra, lightweight, mechanical flexibility, and low cost. Photodetectors with an external quantum efficiency (EQE) greater than 100% are called photomultiplier detectors. In conventional inorganic semiconductor photodetectors, free electrons generated by the dissociation of photogenerated excitons are accelerated in a high electric field to produce superheated electrons, achieving a photomultiplier effect through mechanisms such as collisional excitation or collisional ionization. However, the high exciton binding energy of organic semiconductor materials precludes a similar photomultiplier effect.

[0003] In 1994, Japanese scholars Hiramoto et al. reported for the first time in the document “Hiramoto, M.; Imahigashi, T.; Yokoyama, M., Photocurrent Multiplication In Organic Pigment Films. Appl. Phys. Lett. 1994, 64(2), 187-189.” a multiplication device based on organic material Me-PTC. Its working mechanism is as follows: the interface between the semiconductor and the metal electrode is not absolutely smooth, but there are disordered void defects. Holes are captured and accumulated by these defects during transmission, causing the interface energy band to bend, which in turn causes the external circuit carrier tunneling injection, and ultimately produces a multiplication effect. In 2000, Hiramoto et al. characterized the surface morphology of Me-PTC and its derivatives (n-BU-PTC, PhEt-PTC) by scanning electron microscopy (SEM) in the literature “Nakayama, K.-i.; Hiramoto, M.; Yokoyama, M., Photocurrent multiplication at organic / metal interface and surface morphology of organic films. J. Appl. Phys. 2000, 87(7), 3365-3369.” and confirmed that devices with larger surface roughness have higher multiplication efficiency. Because the surface roughness of the organic film prepared by Hiramoto et al. at that time depended on the intrinsic properties of the material, the defect state at the device interface was uncontrollable, resulting in poor device repeatability. There were not many subsequent related reports (Wang Jian, Zhao Zijin, Yang Kaixuan, Chen Liang, Liu Ming, Zhang Fujun. Research Progress of Multiplication-Type Organic Photodetectors. Acta Polymerica Sinica, 2022, 53(04): 331-353.).

[0004] Inspired by the work of Hiramoto et al., researchers at home and abroad have attempted to use other methods to introduce charge traps to achieve multiplication characteristics. Currently reported multiplication-type organic photodetectors primarily achieve the multiplication effect through two methods: 1) increasing the mass ratio of the donor material to the acceptor material in the photosensitive layer, and 2) introducing a carrier blocking layer / capturing layer into the device. These two methods selectively block a carrier transmission channel in the photosensitive layer, causing it to accumulate at the interface, thereby inducing interface band bending and external circuit carrier tunneling injection, resulting in a multiplication effect. Although several organic multiplication-type photodetectors reported in recent years have achieved significant breakthroughs in performance, they still suffer from problems such as low response speed, high operating voltage, and complex processes. Based on this, the present invention provides a multiplication-type organic photodetector based on high-temperature induced interface traps and a method for preparing the same. Summary of the Invention

[0005] The purpose of the present invention is to address the above-mentioned problems and provide an amplified organic photodetector based on high-temperature induced interface traps to solve the problems in the prior art of uncontrollable surface defect morphology of organic thin films, as well as low response speed, high operating voltage and complex process of the amplified organic photodetector.

[0006] To achieve the above purpose, the technical solution adopted by the present invention is:

[0007] A multiplication-type organic photodetector based on high-temperature induced interface traps comprises: a substrate, a transparent conductive cathode, a cathode modification layer, a photosensitive layer, an anode modification layer and an anode layer stacked in sequence from bottom to top, characterized in that the photosensitive layer undergoes high-temperature thermal annealing treatment to form a granular defect morphology on its upper surface as an interface trap.

[0008] Furthermore, the annealing temperature of the high temperature thermal annealing treatment is 150° C. to 300° C., and the time is 2 min to 300 min.

[0009] Furthermore, the thickness of the photosensitive layer is 100-1000 nm.

[0010] Furthermore, the preparation process of the photosensitive layer is: coating the photosensitive layer mixed solution on the surface of the cathode modification layer to form a thin film, and then performing a high-temperature thermal annealing treatment.

[0011] Furthermore, in the photosensitive layer mixed solution, the organic donor material is one or more of PBDB-T, PM6, and PBDTS-TDZ, the organic acceptor material is Y6, and the mass ratio of the organic donor material to the organic acceptor material is 1:(0.5~10); the organic solvent includes a main solvent and a solvent additive, the main solvent is one or more of chlorobenzene, o-dichlorobenzene, and chloroform, and the solvent additive is one or more of 1,8-diiodooctane (DIO), chloronaphthalene (CN), and nitrobenzene, and the content of the solvent additive is 0.1%~3% (v / v) of the mixed solution; the total concentration in the photosensitive layer mixed solution is 5~100 mg / ml.

[0012] Furthermore, the coating is carried out by spin coating, blade coating, drop coating or spray coating.

[0013] Furthermore, the transparent conductive cathode is an ITO film or a FTO film, the cathode modification layer is made of ZnO, PEIE, TiO2, LiF or SeO2, and the anode modification layer is made of one or more of poly-TPD, PVK, MoO3, P3HT, and PEDOT:PSS.

[0014] Compared with the prior art, the present invention has the following beneficial effects:

[0015] The present invention provides a multiplication-type organic photodetector based on high-temperature induced interface traps. The photosensitive layer is treated by high-temperature thermal annealing to guide the formation of a controllable defect state morphology on its surface. The defect state morphology can be finely controlled by the thermal annealing temperature, annealing time, and thickness of the photosensitive layer. The defect state morphology forms interface traps, causing photogenerated carriers to be trapped and accumulated at the interface, thereby inducing interface energy band bending and tunneling injection of external circuit charges, resulting in a photomultiplier effect. The essential difference from the existing technology (which relies on the Me-PTC system to prepare intrinsic defect state films, increases the mass ratio of donor / acceptor materials in the photosensitive layer, and introduces carrier blocking layers / capture layers) is that the present invention can significantly improve the external quantum efficiency of the device and enhance the detection performance of the detector. At the same time, the device has a low operating voltage and a fast response speed, and the device preparation process is simple and low-cost, making it easy to achieve industrial production. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 This is a schematic structural diagram of the multiplication-type organic photodetector based on high-temperature induced interface traps of the present invention.

[0017] Figure 2 This is an optical microscope image of the surface morphology of the photosensitive layer in the multiplication-type organic photodetector based on high-temperature induced interface traps in Example 1 of the present invention.

[0018] Figure 3Schematic diagram of the contact and carrier transport between the photosensitive layer and the anode modification layer / electrode before and after high-temperature annealing in the present invention.

[0019] Figure 4 Schematic diagram of the working mechanism of the organic photodetector producing the multiplication effect in the present invention.

[0020] Figure 5 This is a spectrum-EQE curve diagram of the multiplication-type organic photodetector based on high-temperature induced interface traps in Example 1 of the present invention. DETAILED DESCRIPTION

[0021] In order to make the objectives, technical solutions, and advantages of the present invention more clearly understood, the present invention is further described in detail below with reference to the accompanying drawings and embodiments. It is obvious that the embodiments described are only part of the embodiments of the present invention, not all of them; all other embodiments derived by persons of ordinary skill in the art based on the embodiments of the present invention without creative effort are also within the scope of protection of the present invention.

[0022] Example 1

[0023] This embodiment provides an amplified organic photodetector based on high temperature induced interface traps, the structure of which is as follows: Figure 1 As shown, it includes: a substrate, a transparent conductive cathode, a cathode modification layer, a photosensitive layer, an anode modification layer and an anode layer stacked in sequence from bottom to top, wherein the photosensitive layer is subjected to high-temperature thermal annealing treatment to form a granular defect morphology on its upper surface as an interface trap.

[0024] This embodiment also provides a method for preparing the above-mentioned multiplication-type organic photodetector based on high-temperature induced interface traps, which specifically includes the following steps:

[0025] Step 1: Cleaning the substrate and drying it with nitrogen after cleaning;

[0026] Step 2: preparing a transparent conductive cathode on the surface of the substrate by magnetron sputtering, thermal evaporation, electron beam evaporation, spin coating, screen printing, spray coating or doctor blade coating, and then cleaning it with ultraviolet ozone;

[0027] Preferably, the substrate is glass or a transparent flexible substrate, and the transparent conductive cathode is an ITO film or an FTO film. In this embodiment, the transparent conductive cathode is ITO, and the substrate and the transparent conductive cathode together constitute an ITO conductive glass.

[0028] Step 3: preparing a cathode modification layer on the surface of the transparent conductive cathode by spin coating, screen printing, spray coating or doctor blade coating;

[0029] Preferably, the cathode modification layer is made of ZnO, PEIE, TiO2, LiF or SeO2; in this embodiment, a ZnO precursor solution is spin-coated on the surface of the transparent conductive cathode ITO, and a thermal annealing treatment is performed under an atmospheric environment to prepare an electron transport layer, i.e., a cathode modification layer; the spin coating speed is 4000 rpm and the time is 40 seconds, and the thermal annealing temperature is 200°C and the time is 30 minutes;

[0030] Step 4: preparing a photosensitive layer on the surface of the cathode modification layer by spin coating, blade coating, drop coating or spray coating, and performing high-temperature thermal annealing after spin coating to obtain the photosensitive layer;

[0031] Preferably, in the spin coating, doctor blade coating, drop coating or spray coating process, the photosensitive layer mixed solution contains an organic semiconductor material having temperature-dependent aggregation behavior, wherein the organic donor material is one or more of PBDB-T, PM6, and PBDTS-TDZ, the organic acceptor material is Y6, and the mass ratio of the organic donor material to the organic acceptor material is 1:(0.5-10); the organic solvent in the photosensitive layer mixed solution contains a main solvent and a solvent additive, wherein the main solvent is one or more of chlorobenzene, o-dichlorobenzene, and chloroform, and the solvent additive is one or more of 1,8-diiodooctane (DIO), chloronaphthalene (CN), and nitrobenzene, and the content of the solvent additive is 0.1% to 3% (v / v) of the mixed solution; the total concentration in the photosensitive layer mixed solution is 5 to 100 mg / ml;

[0032] Preferably, the annealing temperature of the high temperature thermal annealing treatment is 150° C. to 300° C. and the time is 2 min to 300 min;

[0033] Preferably, the thickness of the photosensitive layer is 100 to 1000 nm;

[0034] In this example, an organic donor material PBDB-T and an organic acceptor material Y6 were dissolved in a solvent of chlorobenzene (CB) at a mass ratio of 1:1.2, and 0.5% / v / v chloronaphthalene (CN) was added to obtain a photosensitive layer mixed solution with a total concentration of 50 mg / ml. A photosensitive layer was formed on the surface of the cathode modification layer by spin coating under a nitrogen atmosphere, and then subjected to a high-temperature thermal annealing treatment at 250°C for 10 minutes to obtain a photosensitive layer with a thickness of approximately 500 nm. The spin coating speed was 1500 rpm for 40 seconds.

[0035] Step 5, preparing an anode modification layer (anode modification layer) on the surface of the photosensitive layer by vacuum evaporation or solution method;

[0036] Preferably, the anode modification layer is one or more of poly-TPD, PVK, MoO3, P3HT, and PEDOT:PSS. In this embodiment, the hole transport layer MoO3, i.e., the anode modification layer, is evaporated on the surface of the photosensitive layer at a pressure of 10-4 Pa, thickness is 10nm;

[0037] Step 6: preparing a metal anode on the surface of the anode modification layer by vacuum evaporation, and encapsulating it to obtain an organic photodetector;

[0038] Preferably, the metal anode is one or more of Ag, Al and Au. In this embodiment, the metal anode Ag is evaporated on the surface of the hole transport layer at a pressure of 10 -4 Pa, thickness is 100nm.

[0039] Based on the above preparation method, this embodiment obtains an amplification-type organic photodetector based on high-temperature induced interface traps, whose structure is glass substrate / ITO / ZnO / PBDB-T:Y6 / MoO3 / Ag.

[0040] The mechanism of the present invention is as follows: in the photosensitive layer film that has not been subjected to high temperature thermal annealing treatment, the donor and the acceptor present a uniform nanoscale phase separation morphology, and the film surface is smooth and flat with low roughness (such as Figure 2 As shown in the middle left figure), the photosensitive layer and the anode modification layer / electrode layer (MoO3 / Ag layer) are in close contact, and the carrier transmission is not hindered (as shown in the middle left figure). Figure 3 High-temperature thermal annealing can enhance the diffusion and aggregation of the donor and acceptor material molecules in the photosensitive layer, causing them to form agglomerates in the photosensitive layer and grow based on them as nuclei, ultimately forming a granular defect morphology on the surface of the photosensitive layer, and significantly increasing the roughness of the film (such as Figure 2 As shown in the middle right figure), the contact between the photosensitive layer and the anode modification layer / electrode layer (MoO3 / Ag layer) is no longer close, but there are many defect holes. The carriers cannot be transmitted to the interior of the photosensitive layer or the anode electrode through the defects, and are trapped and accumulated at the defects (as shown in the figure). Figure 3 (as shown in the middle right picture).

[0041] When a positive bias is applied to the device, due to the incomplete contact between the photosensitive layer and the anode modification layer / electrode layer, the holes injected from the anode in the dark state cannot be transferred to the interior of the photosensitive layer through the defects (such as Figure 4 As shown in the middle left figure), the device has a lower dark current under positive bias; under light, the photogenerated electrons generated in the photosensitive layer are transmitted to the interface between the photosensitive layer and the anode modification layer / electrode layer under the action of positive bias, but cannot be transmitted to the anode through the defects and accumulate at the defects. In other words, the defects on the surface of the photosensitive layer form interface traps, which trap and accumulate the photogenerated electrons, induce the bending of the interface energy band, and the holes in the external circuit are injected from the anode through tunneling, thereby producing a photomultiplier effect (as shown in the figure). Figure 4 (as shown in the middle right picture).

[0042] The beneficial effects of the present invention are verified by testing below:

[0043] The spectral response of the multiplication type organic photodetector based on high temperature induced interface traps obtained in this embodiment was tested using the DSR100 wide spectrum photoelectric test system. The test band was 300-1000nm and the test bias voltage was 1-10V. The spectrum-EQE curve of the device was Figure 5 As shown; it can be seen from the figure that even at a bias voltage as low as 1V, the organic photodetector of the present invention still has an EQE of more than 100%, has a wide spectrum of light response and has a photomultiplier effect; and, by appropriately increasing the bias voltage, the device can obtain an EQE of more than 1000%.

[0044] Example 2

[0045] This embodiment provides an amplified organic photodetector based on high-temperature induced interface traps. The only difference between this embodiment and the first embodiment is that the photosensitive layer material, thickness, and high-temperature thermal annealing treatment time are different. Specifically,

[0046] The organic donor material PM6 and the organic acceptor material Y6 were dissolved in a solvent of chlorobenzene (CB) at a mass ratio of 1:1, and 0.3% / v / v chloronaphthalene (CN) was added to obtain a photosensitive layer mixed solution with a total concentration of 30 mg / ml. A photosensitive layer was prepared on the surface of the cathode modification layer by spin coating under a nitrogen atmosphere, and then subjected to high-temperature thermal annealing at 250°C for 60 minutes to obtain a photosensitive layer with a thickness of approximately 200 nm. The spin coating speed was 2000 rpm and the time was 40 seconds.

[0047] The high-temperature induced interface trap multiplication type organic photodetector obtained in this embodiment was tested, and the results were similar to those in Example 1.

[0048] The above description is only a specific embodiment of the present invention. Any feature disclosed in this specification, unless otherwise stated, can be replaced by other equivalent or alternative features with similar purposes; all disclosed features, or all steps in the methods or processes, except for mutually exclusive features and / or steps, can be combined in any way.

Claims

1. A multiplication-type organic photodetector based on high-temperature induced interface traps, comprising: The substrate, transparent conductive cathode, cathode modification layer, photosensitive layer, anode modification layer and anode layer are stacked in sequence from bottom to top, characterized in that the photosensitive layer is subjected to high-temperature thermal annealing treatment to form a granular defect morphology on its upper surface as an interface trap, and the annealing temperature of the high-temperature thermal annealing treatment is 250°C and the time is 10min to 60min.

2. The multiplication-type organic photodetector based on high-temperature induced interface traps according to claim 1, characterized in that: The thickness of the photosensitive layer is 100-1000 nm.

3. The multiplication-type organic photodetector based on high-temperature induced interface traps according to claim 1, characterized in that: The preparation process of the photosensitive layer is as follows: coating the photosensitive layer mixed solution on the surface of the cathode modification layer to form a thin film, and then performing high-temperature thermal annealing treatment.

4. The multiplication-type organic photodetector based on high-temperature induced interface traps according to claim 3, characterized in that: In the photosensitive layer mixed solution, the organic donor material is one or more of PBDB-T, PM6, and PBDTS-TDZ, the organic acceptor material is Y6, and the mass ratio of the organic donor material to the organic acceptor material is 1:(0.5-10); the organic solvent includes a main solvent and a solvent additive, the main solvent is one or more of chlorobenzene, o-dichlorobenzene, and chloroform, and the solvent additive is one or more of 1,8-diiodooctane (DIO), chloronaphthalene (CN), and nitrobenzene, and the content of the solvent additive is 0.1% to 3% (v / v) of the mixed solution; the total concentration in the photosensitive layer mixed solution is 5 to 100 mg / ml.

5. The multiplication-type organic photodetector based on high-temperature induced interface traps according to claim 3, characterized in that: The coating is carried out by spin coating, blade coating, drop coating or spray coating.

6. The multiplication-type organic photodetector based on high-temperature induced interface traps according to claim 1, characterized in that: The transparent conductive cathode is an ITO film or an FTO film, the cathode modification layer is made of ZnO, PEIE, TiO2, LiF or SeO2, and the anode modification layer is made of one or more of poly-TPD, PVK, MoO3, P3HT, and PEDOT:PSS.

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