An organic photodiode with photovoltaic / duplication dual operation mode

Abstract

This invention belongs to the field of organic semiconductor technology, specifically an organic photodiode with dual photovoltaic / multiplication modes. It comprises, from bottom to top, a transparent substrate layer, a first transparent conductive electrode, a first barrier layer, a photosensitive layer, a second barrier layer, and a second electrode. The upper surface of the photosensitive layer has carrier traps for capturing charge carriers. Under forward bias, the carrier traps on the photosensitive layer surface induce carrier tunneling injection into the external circuit, enabling it to operate in PM mode. In this mode, the external quantum efficiency is high, suitable for weak light detection, and avoids the need for a preamplifier circuit. Under reverse bias, the barrier layers on both sides of the photosensitive layer prevent the tunneling injection of charge carriers into the external circuit, enabling it to operate in PV mode. In this mode, the external quantum efficiency is limited, suitable for strong light detection, and avoids problems such as heat dissipation and breakdown caused by high power consumption.

Description

Technical Field

[0001] This invention belongs to the field of organic semiconductor technology, specifically relating to an organic photodiode with photovoltaic / multiplication dual operating modes, suitable for both strong light detection and weak light detection. Background Technology

[0002] Photodiodes have advantages such as low dark current, fast response, small size and easy integration, and are widely used in imaging systems such as CCD / CMOS arrays. Organic photodiodes, in particular, have attracted much attention due to their unique advantages such as flexibility, tunable response spectrum, light weight and low cost.

[0003] Due to the rectification characteristics of photodiodes, the dark current of the device is very high under forward bias, making it unable to detect optical signals. Therefore, photodiodes typically operate under reverse bias based on the photovoltaic (PV) effect. For example, the high-sensitivity perovskite photodetector disclosed in the paper "Recent progress on highly sensitive perovskite photodetectors, J. Mater. Chem. C 2019, 7, 1741" has a low external quantum efficiency (EQE) of no more than 100% when operating in PV mode, as it is equipped with a preamplifier circuit. When detecting weak light signals, the photocurrent generated by a single pixel in a CCD / CMOS array can be as low as pA, but the setup of the preamplifier circuit complicates the imaging system design and increases costs.

[0004] OPDs with photomultiplication (PM) effect have an EQE far greater than 100%, exhibiting strong detection capability for weak light signals and eliminating the need for preamplifier circuits, thus meeting the miniaturization and integration requirements of next-generation imaging systems. For example, a photomultiplication tube-type organic photodetector disclosed in the literature "Recent Progress on Photomultiplication Type Organic Photodetectors, LaserPhotonics Rev. 2018, 13, 1800204" achieves an EQE of 10. 5 It has a photocurrent several orders of magnitude higher than the PV mode, requiring a higher bias voltage for driving, which significantly increases the system's power consumption. Especially when detecting strong light signals, the high power consumption poses a considerable challenge to OPD devices based on organic photosensitive layers, causing problems such as heat dissipation and breakdown.

[0005] It is evident that, regardless of whether it is a PV or PM type device, its single operating mode has limitations and cannot meet the application needs of various scenarios. Summary of the Invention

[0006] To address the aforementioned problems, the present invention aims to provide an organic photodiode with both photovoltaic and multiplication modes, thereby solving the application limitations of existing organic photodiodes due to their single operating mode.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0008] An organic photodiode with photovoltaic / multiplication dual operating modes includes, from bottom to top, a transparent substrate layer, a first transparent conductive electrode, a first barrier layer, a photosensitive layer, a second barrier layer, and a second electrode. The upper surface of the photosensitive layer has carrier traps for trapping charge carriers. Under forward bias, the carrier traps on the surface of the photosensitive layer induce carrier tunneling injection into the external circuit, causing the organic photodiode with photovoltaic / multiplication dual operating modes to operate in PM mode. Under reverse bias, the first barrier layer and the second barrier layer on both sides of the photosensitive layer prevent the tunneling injection of charge carriers into the external circuit, causing the organic photodiode with photovoltaic / multiplication dual operating modes to operate in PV mode.

[0009] Furthermore, the photosensitive layer comprises one or more organic semiconductor materials.

[0010] Furthermore, the photosensitive layer is prepared by: applying an organic semiconductor mixed solution for preparing the photosensitive layer onto the upper surface of the first barrier layer to form a thin film through spin coating, blade coating, drop coating, spray coating or vapor deposition processes; and then performing thermal annealing, solvent annealing, nanoimprinting, template growth or vapor deposition processes to adjust the morphology of granular defects or concave defects on the upper surface and / or lower surface of the thin film.

[0011] Furthermore, the morphology roughness and pore size of the particle defects can be adjusted according to requirements.

[0012] Furthermore, both the first and second blocking layers can be electron blocking layers or hole blocking layers. Electron blocking layer materials include poly-TPD, PVK, MoO3, P3HT, and PEDOT:PSS, while hole blocking layer materials include ZnO, PEIE, PEIE-Zn, TiO2, LiF, and SeO2.

[0013] Furthermore, the thickness of the photosensitive layer is 100nm to 2000nm.

[0014] This invention provides an organic photodiode with both photovoltaic (PV) and photomultiplier (PM) operating modes, which are controlled by the direction of the applied bias voltage to meet the application requirements of strong and weak light detection. Under forward bias, carrier traps on the photosensitive layer surface induce carrier tunneling injection into the external circuit, causing the organic photodiode to operate in PM mode. In this mode, the external quantum efficiency is high, making it suitable for weak light detection and eliminating the need for a preamplifier circuit. Under reverse bias, the blocking layers on both sides of the photosensitive layer prevent carrier tunneling injection into the external circuit, causing the organic photodiode to operate in PV mode. In this mode, the external quantum efficiency is limited, making it suitable for strong light detection and avoiding problems such as heat dissipation and breakdown caused by high power consumption. Attached Figure Description

[0015] Figure 1 This is a schematic diagram of the device structure of the organic photodiode with photovoltaic / multiplication dual operating modes in this invention;

[0016] Figure 2 Optical microscope image of the upper surface of the photosensitive layer in an organic photodiode with photovoltaic / multiplication dual operating modes prepared in Example 1;

[0017] Figure 3 The schematic diagram shows the working principle of the organic photodiode with photovoltaic / multiplication dual operating modes prepared in Example 1;

[0018] Figure 4 The EQE spectral response diagram of the organic photodiode with photovoltaic / multiplication dual operating modes prepared in Example 1. Detailed Implementation

[0019] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. Obviously, the described embodiments are only some, not all, of the embodiments of this invention; all other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0020] Example 1

[0021] This embodiment provides an organic photodiode with both photovoltaic and multiplication modes, the structure of which is as follows: Figure 1 As shown, an organic photodiode with photovoltaic / multiplication dual operating modes includes, from bottom to top, a transparent substrate layer, a transparent conductive electrode 1, a barrier layer 1, an organic photosensitive layer, a barrier layer 2, and a second electrode 2; the upper surface of the organic photosensitive layer has a carrier trap for capturing carriers.

[0022] The aforementioned organic photodiode with both photovoltaic and multiplication modes employs an inversion structure, and its fabrication method specifically includes the following steps:

[0023] Step 1: Clean the transparent glass substrate and dry it with nitrogen. Deposit an ITO thin film with a thickness of 150 nm on the surface of the transparent glass substrate using magnetron sputtering. Clean the glass substrate with the deposited ITO film in sequence with detergent, acetone and isopropanol, then blow it with nitrogen and treat it with ultraviolet ozone for 15 min to obtain a transparent conductive electrode.

[0024] Step 2: In this embodiment, the blocking layer 1 serves as a hole blocking layer and is a ZnO thin film. The ZnO precursor solution is uniformly coated onto the transparent conductive electrode 1 by spin coating. The spin coating speed and time are 4000 rpm and 40 s, respectively. The electrode is then subjected to thermal annealing in an atmospheric environment. The thermal annealing temperature and time are 200℃ and 30 min, respectively.

[0025] Step 3: Using organic semiconductor materials PBDB-T and Y6 as photosensitive layer materials, they were dissolved in the organic solvent chlorobenzene at a mass ratio of 1:1.2, resulting in a total solution concentration of 30 mg / ml. The solution was then stirred on a heated stirring table at 60°C for at least 12 hours. Under a nitrogen atmosphere, a photosensitive layer was prepared on the surface of the ZnO hole-blocking layer using a spin-coating process. The spin-coating speed and time were 5000 rpm and 40 s, respectively, resulting in an organic photosensitive layer with a thickness of approximately 200 nm.

[0026] Step 4: Form carrier traps for capturing charge carriers on the upper and / or lower surfaces of the organic photosensitive layer obtained in Step 3. In this embodiment, the carrier traps are formed on the upper surface of the organic photosensitive layer, which are particulate defect morphologies formed by thermal annealing. The temperature and time of the thermal annealing are 200°C and 30 min, respectively.

[0027] Step 5: In this embodiment, the blocking layer 2 serves as an electron blocking layer and is prepared on the surface of the organic photosensitive layer using vacuum evaporation. The evaporation pressure is 10⁻⁶. 4 Pa. The electron blocking layer material is MoO3, with a thickness of 10 nm.

[0028] Step 6: Deposit an electrode onto the surface of the electron blocking layer obtained in Step 5. The electrode material is metallic Ag, and the deposition pressure is 10⁻⁶. 4 Pa, with a thickness of 100 nm.

[0029] A control group was prepared according to the above steps. The control group had the same structure as the photodiode in Example 1, but the organic photosensitive layer surface of the control group did not have carrier traps.

[0030] Figure 2An optical microscope image of the photosensitive layer of an organic photodiode with photovoltaic / multiplication dual operating modes and its control group device, as shown below. Figure 2 As shown, the upper surface of the photosensitive layer of the control group device that has not undergone thermal annealing is smooth and flat, while after thermal annealing, the morphology of the upper surface of the photosensitive layer changes and more particles appear.

[0031] The mechanism of this invention is as follows: by controlling the morphology of the upper and / or lower surface of the photosensitive layer, the contact between it and the blocking layer becomes less uniform and tight, hindering the transport of charge carriers and causing them to accumulate at the contact interface, which is equivalent to introducing a charge carrier trap at the interface. Figure 3 As shown, the organic photodiode with photovoltaic / multiplication dual operating modes in Example 1 exhibits a low dark current under reverse bias due to the energy level blocking of the ZnO and MoO3 blocking layers. When illuminated, photogenerated electrons / holes in the photosensitive layer are collected by the ITO / Ag electrodes to generate photocurrent, i.e., it operates in PV mode. Under forward bias, due to the obstruction of carrier transport at the organic photosensitive layer interface, its dark current is reduced compared to the control group device without carrier traps in the organic photosensitive layer. When illuminated, the carrier traps on the surface of the organic photosensitive layer and the blocking of the MoO3 layer cause photogenerated electrons and electrons injected from the external circuit to be trapped at the organic photosensitive layer / MoO3 interface, while photogenerated holes are blocked by the ZnO layer and then accumulate at the ZnO / photosensitive layer interface. As carriers are trapped at the interface and accumulate, the bending of the interface band is enhanced, eventually causing hole tunneling injection, thus generating the PM effect. Therefore, the organic photodiode with photovoltaic / multiplication dual operating modes of Example 1 can operate in PM and PV modes under forward and directional bias, respectively.

[0032] The technical effects of the present invention are verified below through specific experimental data:

[0033] The organic photodiode with photovoltaic / multiplication dual operating modes of Example 1 and its control group devices were tested in the wavelength range of 300–1000 nm. (See also...) Figure 4 It can be seen that the organic photodiode device with photovoltaic / multiplication dual operating modes in Example 1 operates in PV mode at a -2V bias voltage, with an EQE of less than 100%; at a +2V bias voltage, the device can achieve an EQE of over 1000%, operating in PM mode. In contrast, the control group device can only operate in PV mode under reverse bias voltage.

[0034] Example 2

[0035] The difference between Example 2 and Example 1 lies in the process of forming carrier traps on the surface of the photosensitive layer. Example 2 uses a nanoimprinting process to prepare a uniformly distributed array of recesses on the upper surface of the organic photosensitive layer to form carrier traps.

[0036] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. An organic photodiode with photovoltaic / multiplication dual operating modes, comprising, from bottom to top, a transparent substrate layer, a first transparent conductive electrode, a first blocking layer, a photosensitive layer, a second blocking layer, and a second electrode; characterized in that: The upper surface of the photosensitive layer has carrier traps for capturing carriers; under forward bias, the carrier traps on the surface of the photosensitive layer cause carrier tunneling injection into the external circuit, so that the organic photodiode with photovoltaic / multiplication dual working modes operates in photomultiplication mode. Under reverse bias, the first and second blocking layers on both sides of the photosensitive layer prevent the tunneling injection of charge carriers from the external circuit, enabling the organic photodiode with photovoltaic / multiplication dual operating modes to operate in photovoltaic mode.

2. The organic photodiode with photovoltaic / multiplication dual operating modes according to claim 1, characterized in that: The photosensitive layer contains one or more organic semiconductor materials.

3. An organic photodiode with photovoltaic / multiplication dual operating modes according to claim 1, characterized in that, The photosensitive layer is prepared by: applying an organic semiconductor mixed solution for preparing the photosensitive layer onto the upper surface of the first barrier layer to form a thin film through spin coating, blade coating, drop coating, spray coating or vapor deposition processes; and then performing thermal annealing, solvent annealing, nanoimprinting, template growth or vapor deposition processes to adjust the morphology of granular defects or concave defects on the upper surface and / or lower surface of the thin film.

4. An organic photodiode with photovoltaic / multiplication dual operating modes according to claim 3, characterized in that: The roughness of the particle defect morphology can be adjusted according to requirements.

5. An organic photodiode with photovoltaic / multiplication dual operating modes according to claim 1, characterized in that, Both the first and second blocking layers can be electron blocking layers or hole blocking layers. Electron blocking layer materials include poly-TPD, PVK, MoO3, P3HT and PEDOT:PSS, and hole blocking layer materials include ZnO, PEIE, PEIE-Zn, TiO2, LiF and SeO2.

6. An organic photodiode with photovoltaic / multiplication dual operating modes according to claim 4, characterized in that, The thickness of the photosensitive layer is 100nm to 2000nm.

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