Siloxane d-a-d type perylene imide small molecule electron transport layer and preparation method thereof

Abstract

The application discloses a siloxane D-A-D type perylene diimide small-molecule electronic transport layer and a preparation method thereof. Bromine perylene diimide is reacted with a primary amine containing a siloxane end group, and then is coupled with triphenylamine through a Suzuki coupling reaction to synthesize a small-molecule conjugated electrolyte. The siloxane D-A-D type perylene diimide small-molecule electronic transport layer has the following beneficial effects: first, the secondary amine in the side chain can form hydrogen bonds with F and H in the active layer, improve the interface compatibility, and improve the contact with the active layer; second, the D-A-D structure can realize intramolecular charge transfer, and excellent electron mobility can be exhibited; third, a good n-type self-doping is obtained, the work function of a high-stability metal Ag can be reduced, an ohmic contact is formed, and therefore the photovoltaic performance of a device is significantly improved; fourth, the stability can be improved due to the hydrophobicity of the siloxane; and finally, triphenylamine has a special non-planar molecular structure, and can inhibit excessive aggregation of the material.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of organic solar cell electron transport layer, and particularly relates to a siloxane D-A-D type perylene diimide small molecule electron transport layer and a preparation method thereof. BACKGROUND

[0002] With the development of the times, the non-renewable resources on the earth are becoming less and less. With the large-scale exploitation and use of fossil energy, the environmental pollution problem on the earth is becoming more and more serious. The research of green renewable energy has become a new development trend and has been paid attention by researchers in various fields. Solar energy is one of the most ideal green renewable energies on the earth, which has the characteristics of inexhaustible, zero pollution and low risk, and has rapidly become a research hotspot of green renewable energy in recent years. At present, scientists are constantly researching how to develop and utilize solar energy, and it can be said that the preparation of solar cells is the most convenient and effective method.

[0003] With the continuous progress of human civilization, the environmental pollution caused by fossil energy shortage and increasing energy demand has become a key factor hindering the sustainable development of human culture. Therefore, the development and utilization of new energy have attracted the attention of countries around the world. Among all renewable energies, solar energy is considered to be one of the most promising energies to solve the energy crisis. So far, scientists have made relatively in-depth research on solar cells. Inorganic solar cells are the most widely used in the market, accounting for more than 80% in the solar cell industry, and the most popular ones are single-crystal silicon solar cells and polycrystalline silicon solar cells. This type of cell has excellent performance, and the photoelectric conversion efficiency is at a high level, almost reaching the theoretical efficiency (30%). But in the actual operation, it has to consider the high cost, high energy consumption and high pollution in the production process, such as Si-based solar cells, which have complex process and high energy consumption in controlling the synthesis of single-crystal silicon, which leads to the high price of crystalline silicon solar cells in the market, which is the main reason for limiting its application and development. Non-fullerene organic solar cells (NOSCs) have attracted increasing attention from academia and the market due to their low production cost, light weight, excellent mechanical properties, and ease of large-scale production. In addition, due to the successful application of high-performance acceptors, such as the invention of A (acceptor)-D (donor)-A type and A-D-A-D-A type non-fullerene acceptors (NFAs), such as ITIC and Y6, the performance of NOSCs has been greatly improved. With these NFAs, the power conversion efficiency (PCE) of NOSCs in single-junction devices has reached more than 19%, and the power conversion efficiency of series-connected devices has reached more than 20%, showing the practical application prospect of NOSCs.

[0004] In addition to the high performance NOSCs' light absorption, the transport and collection of charges are also critical aspects. Generally, there is a clear Schottky barrier between the metal electrode and the organic active layer, resulting in a potential energy loss. Therefore, electron transport materials (ETM) are as important as the active layer in driving NOSCs towards commercialization, which can prevent the recombination of carriers on the cathode, improve the stability of the device, thus providing matching energy levels and facilitating the charge transport and extraction in the device. SUMMARY

[0005] In order to overcome the deficiencies of the prior art, the present application provides a siloxane D-A-D type perylene diimide small molecule electron transport layer and a preparation method thereof. The existing electron transport layer mainly includes metal oxides, metal fluorides, organic small molecules, organic conjugated polymer electrolytes and fullerene derivatives. However, the existing electron transport layer can only play a role in regulating the interface work function and reducing the interface barrier between the active layer and the cathode, and cannot solve the four aspects of active layer morphology, electron mobility, interface barrier and stability. The preparation and application of a siloxane-terminated D-A-D type perylene diimide small molecule electron transport layer designed by the present application has many advantages.

[0006] Among the many interlayer materials, water / alcohol-soluble organic interlayers are widely studied due to their processability in low-temperature solutions. Many reported small molecule and polymer ETMs are water / alcohol-soluble, with potential commercial application prospects. Compared with polymer materials, water / alcohol-soluble small molecule conjugated electrolytes (SMCEs) with high polar groups are of great interest due to their clear chemical structure, good batch reproducibility, simple synthesis and purification, etc. More importantly, SMCEs can be easily modified towards appropriate energy levels and optical / electrical properties to match different active layers. In order to enhance the ability to reduce the work function (WF) of high-stability metal silver and limit the recombination of electron-hole pairs, it is necessary to introduce ETMs with polar groups in NOSCs. So far, a series of high-efficiency small molecule ETM materials, such as naphthalene diimide (NDI) and perylene diimide (PDI) derivatives containing amine groups or amine group N-oxides, have become a research hotspot due to their good electron transport performance, easy chemical modification and suitable energy levels. However, the strong π-π stacking between PDI and NDI planes always leads to face-to-face stacking and excessive crystal aggregation, which may destroy the related photoelectric properties. It is well known that suitable crystal aggregation, good thermal stability and excellent solution processability are the keys for ETMS to explore efficient NOSCs. Therefore, it is crucial to design and produce various n-type ETMs with flexible molecular configurations and various polar side groups.

[0007] Due to the lack of electron-accepting properties, PDI can be applied to n-type SMCEs and acceptor units of D-A molecules. In addition, PDI-based materials can produce strong π-π interactions and electron-attracting effects due to their good conjugated structure. In addition, PDI-based materials exhibit excellent electron mobility; excellent electron mobility enables ETMs to meet future large-scale printing technology without sacrificing the device performance of NOSCs and exhibit excellent thickness-insensitive characteristics. A large number of PDI-based D-A type semiconductor materials have been successfully developed, all of which have exhibited excellent photovoltaic performance. In addition, the PDI bay area can be easily adapted to various substitutions, which can effectively adjust the band gap (E g ), electron mobility, energy level and film morphology of PDI materials. When PDI is co-polymerized or connected with electron-rich units, the highest occupied molecular orbital (HOMO) of PDI materials can be lowered, which is beneficial to block hole transport. At the same time, E g becomes narrower. In addition, six different twist blocks have also been applied to the core unit to adjust the interaction. Due to the sp3 hybrid orbital of the nitrogen atom, triphenylamine has a special non-planar molecular structure, which can effectively extend the π conjugation, inhibit the excessive aggregation of crystals, and improve the processability of the solution. In addition, TPA-based materials have isotropic charge transport characteristics due to their quasi-three-dimensional structure. In addition, TPA has been widely used in various optoelectronic applications due to its excellent photophysical, electrochemical, thermal properties and carrier mobility. Therefore, the introduction of electron-rich TPA groups on the electron-deficient central backbone can improve π conjugation, carrier mobility and optoelectronic performance. At the same time, due to the hydrophobicity of siloxane, the air stability of the molecule can be effectively improved.

[0008] D-A-D type SMCEs have been proven to be a successful strategy and have recently received extensive attention. D-A-D type structure can properly adjust the molecular frontier orbital energy level by selecting adjacent D and A units to form a suitable energy arrangement. More importantly, due to strong dipole-dipole interactions and effective intramolecular charge transfer (ICT), D-A-D type SCMEs show excellent electron mobility and n-type self-doping. This can promote the accumulation of molecules, thereby improving the electron transport capacity.

[0009] The application synthesizes two D-A-D type SMCEs with PDI as acceptor, TPA as donor and siloxane end group polar branch, PDINSi3(TPA)2.The introduction of PDI lacking of electron provides n-type core, so that the SMCE has self-doped electron absorption capacity, thereby improving the ICT of the SMCE.Meanwhile, the introduction of TPA donor unit can expand the pi conjugated system and adjust the photoelectric performance.More importantly, the TPA core can reasonably adjust the energy gap and energy level of the PDI core.In addition, the siloxane end group polar branch is added to adjust the stability of the SMCE.Because of the existence of TPA and the polar side group, the PDINSi3(TPA)2 can be easily dissolved in various polar solvents.Benefiting from the n-type D-A-D conjugated core and the ICT of the amine side chain, the n-type self-doping is obtained.These n-type self-doping SMCEs can have good electron mobility and reduce the WF of the stable metal Ag to produce ohmic contact, thereby significantly improving the photovoltaic performance of the SMCE.Especially, the siloxane has hydrophobicity, which can effectively improve the moisture stability of the molecule.

[0010] The application provides a preparation and application of a siloxane-terminated D-A-D type perylene diimide small-molecule electron transport layer.

[0011] The application provides a preparation and application of a siloxane-terminated D-A-D type perylene diimide small-molecule electron transport layer.

[0012] The application adopts the technical scheme as follows: a siloxane D-A-D type perylene diimide small-molecule electron transport layer has the structure shown in formula I, and the structure is as follows:

[0013]

[0014] Another technical scheme of the application is as follows: a preparation method of a siloxane D-A-D type perylene diimide small-molecule electron transport layer with the structure shown in formula I, and the preparation method comprises the following steps:

[0015] Step one: synthesis of a primary amine derivative containing a siloxane end group;

[0016] (1) N-(2-aminoethyl)-3-aminopropyltrimethoxysilane 10.0mmol, hexamethyldisiloxane 50.0mmol and potassium hydroxide 0.5mmol are put into a round-bottom flask (100mL) provided with a condenser tube;

[0017] (2) The flask was evacuated and refilled with nitrogen four times, then placed in a 100 °C oil bath and stirring was continued under nitrogen for 3.0 h;

[0018] (3) The temperature was raised to 140 °C and maintained for 0.5 h. After the flask was cooled to room temperature, the mixture was poured into 30 mL of deionized water;

[0019] (4) The upper layer was extracted after the mixture was left for 4.0 h. The above similar procedure was repeated 3 times until the upper layer became transparent;

[0020] (5) The mixture was diluted with anhydrous dichloromethane, dried with anhydrous Na2S04, filtered and dried under vacuum to obtain a light yellow liquid (73%).

[0021] Step two: synthesis of PDINSi3;

[0022] (1) 1 mmol of PDIBr and 2 mmol of the product from the previous step were dissolved in 20 mL of super dry DMF and 1 mmol of zinc acetate was added as a catalyst;

[0023] (2) The flask was evacuated and refilled with nitrogen four times, then placed in a 140 °C oil bath and stirring was continued under nitrogen for 24 h;

[0024] (3) After the reaction was completed, the reaction mixture was cooled to room temperature and the reaction solvent was removed by vacuum distillation;

[0025] (4) The upper layer was removed after dichloromethane and water were added. The above similar procedure was repeated 5 times until the upper layer became transparent. The upper layer was removed and rotary evaporated, and recrystallized with methanol. Finally, a red-brown solid was obtained with a yield of 75%.

[0026] Step three: synthesis of a siloxane-terminated D-A-D type perylene diimide small molecule PDINSi3(TPA)2.

[0027] (1) 0.2 mmol of PDINSi3 and 0.5 mmol of 3-boronic acid triphenylamine farnesol ester were added to a dried 100 mL reaction flask, and 50 mg of catalyst Pd(dppf)Cl2 was added. The flask was sealed under a nitrogen atmosphere.

[0028] (2) Then 20 mL of deoxygenated tetrahydrofuran and 5 mL of deoxygenated K2C03(2M) aqueous solution were slowly added to the flask. The reaction flask was vacuumed and filled with nitrogen 5 times using nitrogen. The air in the reaction flask was replaced with N2. The reaction mixture was stirred at 65 °C for 24 hours.

[0029] (3) After cooling to room temperature, add dichloromethane and water, take out the upper layer, repeat the above similar procedure 5 times until the upper layer becomes transparent, remove the dichloromethane by a rotary evaporator under reduced pressure. The crude product is purified by column chromatography to obtain a red-brown solid PDINSi3(TPA)2, which is vacuum dried at 60℃ for 24h, with a yield of 61%.

[0030] Another technical solution of the present application is as follows: a non-fullerene solar cell device of a siloxane-terminated D-A-D type perylene diimide small molecule electron transport layer, characterized in that:

[0031] It comprises an ITO glass layer, a PEDOT:PSS anode interface layer arranged on the ITO glass layer, an active layer arranged on the PEDOT:PSS anode interface layer, a D siloxane-terminated D-A-D type perylene diimide small molecule PDINSi3(TPA)2 electron transport layer arranged on the active layer, and an Ag electrode arranged on the electron transport layer.

[0032] Another technical solution of the present application is as follows: a synthesis method of a siloxane D-A-D type perylene diimide small molecule electron transport layer PDINSi3(TPA)2, characterized in that: the specific synthesis route reaction equation II is as follows:

[0033]

[0034] Compared with the prior art, the present application has the beneficial effects of strong innovation, combination of five advantages of high conductivity and high electron mobility of PDI, n-type self-doping effect, moisture-proof stability of siloxane, environmentally friendly water / alcohol soluble processing, and better compatibility with the active layer. The five problems of unideal active layer morphology, low carrier mobility, interface potential barrier between the active layer and the electrode, easy moisture absorption of the device in air, and easy excessive aggregation of PDI molecules can be solved at the same time:

[0035] (1) The secondary amine in the side chain can form hydrogen bonds with F and H in the active layer, improve the interface compatibility, and improve the contact with the active layer;

[0036] (2) The PDI lacking of electrons is to provide an n-type core and has a self-doped electron absorption capacity. The PDI-based material shows excellent electron mobility. The excellent electron mobility enables the ETMs to meet the future large-scale printing technology without sacrificing the device performance of the NOSC and shows excellent thickness insensitivity characteristics;

[0037] (3) The lone pair of electrons on the nitrogen of triphenylamine can be transferred to the electron-withdrawing perylene diimide backbone, benefiting from the n-type D-A-D conjugated core and side chain ICT, forming an n-type self-doping effect, which helps to form a large interface dipole and improve the conductivity of the material, can reduce the WF of the stable metal Ag to produce ohmic contact, reduce the interface barrier, thereby improving the open-circuit voltage and short-circuit current of the device. And can avoid the destruction of the stability of the device by external doping, obtain a thickness-insensitive electron transport layer, and lay the foundation for future large-area roll-to-roll solution printing production.

[0038] (4) The siloxane has hydrophobicity, which can effectively improve the moisture stability of the molecule;

[0039] (5) Triphenylamine has a special non-planar molecular structure, which can effectively extend the pi conjugation and inhibit the excessive aggregation of crystals. In addition, the TPA-based material has isotropic charge transport characteristics due to its quasi-three-dimensional structure, and the energy level of PDI can be fine-tuned to be more matched with the acceptor of the active layer. Due to the presence of TPA and polar side groups, PDINSi3(TPA)2 can be easily dissolved in various polar solvents, and has the characteristics of environmentally friendly solvent processing. BRIEF DESCRIPTION OF DRAWINGS

[0040] Figure 1 It is a structure diagram of a siloxane D-A-D type perylene diimide small molecule electron transport layer PDINSi3(TPA)2 of the present application.

[0041] Figure 2 It is a device structure diagram of a siloxane D-A-D type perylene diimide small molecule electron transport layer PDINSi3(TPA)2 based on the present application.

[0042] Figure 3 It is a specific reaction equation diagram of a siloxane D-A-D type perylene diimide small molecule electron transport layer PDINSi3(TPA)2 of the present application. DETAILED DESCRIPTION

[0043] The present application will be further described below in conjunction with the drawings.

[0044] The reaction equation of the present application is as follows: Figure 3 The specific reaction steps are as follows: the synthesis steps of a siloxane D-A-D type perylene diimide small molecule electron transport layer PDINSi3(TPA)2 are as follows:

[0045] Step one: synthesis of primary amine derivative containing siloxane end group;

[0046] (1) Put N-(2-aminoethyl)-3-aminopropyltrimethoxysilane 10.0 mmol, hexamethyldisiloxane 50.0 mmol and potassium hydroxide 0.5 mmol into a round bottom flask (100 mL) with a condenser tube;

[0047] (2) The flask was vacuumed and refilled with nitrogen four times, then put into an oil bath at 100°C, and continue to stir for 3.0 h under nitrogen protection;

[0048] (3) The temperature was raised to 140°C and kept for 0.5 h. After the flask was cooled to room temperature, the mixture was poured into 30 mL of deionized water;

[0049] (4) After the above mixture was placed for 4.0 h, the upper layer was extracted, and the above similar procedure was repeated 3 times until the upper layer became transparent;

[0050] (5) The mixture was diluted with anhydrous dichloromethane, dried with anhydrous Na2SO4, filtered and dried under vacuum to obtain a light yellow liquid (73%).

[0051] Step two: synthesis of PDINSi3;

[0052] (1) Dissolve 1 mmol of PDIBr and 2 mmol of the product of the previous step in 20 mL of super dry DMF and add 1 mmol of zinc acetate as a catalyst;

[0053] (2) The flask was vacuumed and refilled with nitrogen four times, then put into an oil bath at 140°C, and continue to stir for 24 h under nitrogen protection;

[0054] (3) After the reaction was completed, the reaction mixture was cooled to room temperature, and the reaction solvent was removed by reduced pressure distillation;

[0055] (4) After dichloromethane and water were added, the lower layer was taken out, and the above similar procedure was repeated 5 times until the upper layer became transparent, the lower layer was taken out for rotary evaporation, and recrystallized with methanol, finally a red-brown solid was obtained with a yield of 75%.

[0056] Step three: synthesis of a siloxane D-A-D type perylene imide small molecule electron transport layer PDINSi3(TPA)2:

[0057] (1) Add 0.2 mmol of PDINSi3 and 0.5 mmol of 3-boronic acid triphenylamine farnesol ester to a dried 100 mL reaction flask, and add 50 mg of catalyst Pd(dppf)Cl2, and seal under nitrogen atmosphere.

[0058] (2) Then 20 mL of deoxygenated tetrahydrofuran and 5 mL of deoxygenated K2CO3 (2M) aqueous solution were slowly added into the flask, the reaction mixture was stirred at 65℃ for 24 hours after 5 times of vacuum and nitrogen replacement.

[0059] (3) After cooling to room temperature, the upper layer was removed after adding dichloromethane and water, and the above similar procedure was repeated 5 times until the upper layer became transparent, and the dichloromethane was removed by a rotary evaporator under reduced pressure. The crude product was purified by column chromatography to obtain a red-brown solid PDINSi3(TPA)2, which was vacuum dried at 60℃ for 24h, with a yield of 61%.

[0060] The beneficial effects of the present application are that the five big problems of unsatisfactory active layer morphology, low carrier mobility, interface potential barrier between active layer and electrode, device moisture stability and easy excessive aggregation of PDI molecules can be solved at the same time:

[0061] (1) The secondary amine in the side chain can form hydrogen bonds with F and H in the active layer, improve the interface compatibility, and improve the contact with the active layer;

[0062] (2) The PDI lacking of electron is to provide n-type core, and has self-doped electron absorption capacity, and the PDI-based material shows excellent electron mobility; The excellent electron mobility enables ETMs to meet the future large-scale printing technology without sacrificing the device performance of NOSC and exhibit excellent thickness insensitivity characteristics;

[0063] (3) The lone pair electrons of nitrogen on triphenylamine can be transferred to the electron-withdrawing perylene diimide main chain, benefiting from the n-type D-A-D conjugated core and the ICT of the side chain, forming an n-type self-doping effect, which helps to form a large interface dipole and improve the conductivity of the material, can reduce the WF of high-stability metal Ag to produce ohmic contact, reduce the interface potential barrier, thereby improving the open-circuit voltage and short-circuit current of the device. And can avoid the damage of external doping to the stability of the device, obtain the thickness-insensitive electron transport layer, and lay the foundation for the realization of large-area roll-to-roll solution printing production in the future.

[0064] (4) The siloxane has hydrophobicity, which can effectively improve the moisture stability of the molecule;

[0065] (5) Triphenylamine has a special non-planar molecular structure, which can effectively extend the π-conjugation and inhibit the excessive aggregation of crystals. In addition, the TPA-based material has isotropic charge transport characteristics due to its quasi-three-dimensional structure, and the energy level of PDI can be fine-tuned to match the active layer acceptor better. Due to the existence of TPA and polar side groups, PDINSi3(TPA)2 can be easily dissolved in various polar solvents, and has the characteristics of green solvent processing.

Claims

1. A siloxane D-A-D perylene imide small molecule electron transport layer characterized by: having the structure of Formula I, as follows: Formula I.

2. A method for preparing a siloxane D-A-D type perylene imide small molecule electron transport layer according to claim 1, characterized by: The siloxane D-A-D type perylene imide small molecule electron transport layer is PDINSi3(TPA)2, comprising the following steps: Step S1: synthesis of primary amine derivatives containing siloxane end groups; Step S2: synthesis of PDINSi3; Step S3: synthesis of siloxane-terminated D-A-D type perylene imide small molecule PDINSi3(TPA)2; The specific synthesis route reaction equation II is as follows: Formula II.

3. A preparation method of a siloxane D-A-D type perylene imide small molecule electron transport layer according to claim 2, characterized in that: The synthesis of primary amine derivatives containing siloxane end groups has the following specific steps: Step S11, N-(2-aminoethyl)-3-aminopropyl trimethoxysilane 10.0 mmol, hexamethyldisiloxane 50.0 mmol and potassium hydroxide 0.5 mmol are placed in a round-bottom flask equipped with a condenser; Step S12, the flask is vacuumed, recharged with nitrogen, repeated four times, then placed in a 100°C oil bath, continue to stir under nitrogen protection for 3.0h; Step S13, the temperature is raised to 140°C and kept for 0.5h, after the flask is cooled to room temperature, the mixture is poured into 30 mL deionized water; Step S14, after the above mixture is placed for 4.0h, the upper layer is extracted, and the above procedure is repeated for 3 times until the upper layer becomes transparent; Step S15, the mixture is diluted with anhydrous dichloromethane, dried with anhydrous Na2SO4, filtered and dried under vacuum to obtain a light yellow liquid.

4. A preparation method of a siloxane D-A-D type perylene imide small molecule electron transport layer according to claim 3, characterized in that: The synthesis of PDINSi3 has the following specific steps: Step S21, 1 mmol of PDINBr and 2 mmol of the product of the previous step are dissolved in 20 mL of super dry DMF and 1 mmol of zinc acetate is added as a catalyst; Step S22, vacuum, recharged with nitrogen, repeated four times, then placed in a 140°C oil bath, continue to stir under nitrogen protection for 24h; Step S23, after the reaction is completed, the reaction mixture is cooled to room temperature, and the reaction solvent is removed by vacuum distillation; Step S24, after dichloromethane and water are added, the lower layer is taken out, and the above procedure is repeated for 5 times until the upper layer becomes transparent, the lower layer is taken out for rotary evaporation, and recrystallized with methanol, finally a red-brown solid is obtained, with a yield of 75%.

5. A preparation method of a siloxane D-A-D type perylene imide small molecule electron transport layer according to claim 4, The synthesis of siloxane-terminated D-A-D type perylene imide small molecule PDINSi3(TPA)2 has the following specific steps: Step S31, 0.2 mmol of PDINSi3 and 0.5 mmol of 3-boronic acid triphenylamine farnesol ester are added to a dried 100 mL reaction bottle, and 50 mg of catalyst Pd(dppf)Cl2 is added, and the bottle is sealed under nitrogen atmosphere; Step S32, then 20 mL of deoxygenated tetrahydrofuran and 5 mL of deoxygenated K2CO3 aqueous solution were slowly added into the flask, the reaction mixture was stirred at 65℃ for 24 hours after 5 times of vacuum pumping and nitrogen replacement; Step S33, after cooling to room temperature, the upper layer was taken out after adding dichloromethane and water, and the above procedure was repeated 5 times until the upper layer became transparent, and the dichloromethane was removed by a rotary evaporator under reduced pressure; the crude product was purified by column chromatography to obtain a red-brown solid PDINSi3(TPA)2, which was vacuum dried at 60℃ for 24 h, with a yield of 61%.

6. A non-fullerene solar cell device, characterized by: The device comprises an ITO glass layer, a PEDOT: PSS anode interface layer arranged on the ITO glass layer, an active layer arranged on the PEDOT: PSS anode interface layer, a PDINSi3(TPA)2 electron transport layer arranged on the active layer, wherein the electron transport layer refers to the siloxane D-A-D type perylene imide small molecule electron transport layer of claim 1, and an Ag electrode arranged on the electron transport layer.

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