Stable perovskite precursor solution, perovskite solar cell and preparation method thereof
By adding boron-containing compounds to the perovskite precursor solution, the problem of easy aging of the perovskite precursor solution was solved, the stability of the solution and the repeatability of the device were improved, and the industrial application of perovskite solar cells was promoted.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- SHANGHAI BOGUANG ERA NEW ENERGY TECHNOLOGY CO LTD
- Filing Date
- 2026-01-23
- Publication Date
- 2026-05-01
AI Technical Summary
Perovskite precursor solutions are prone to aging, which leads to a decline in device performance and reproducibility, affects the grain size, crystallinity, and film quality of perovskite films, and thus hinders the realization of stable and high-performance perovskite solar cells.
Boron-containing compounds were used as additives to stabilize perovskite precursor solutions. By forming strong interactions between the empty outer orbitals of the boron atoms and halide anions, the generation of hydroiodic acid was inhibited, and the deprotonation process of methylamine cations and formamidinium cations was blocked, thus preparing stable perovskite precursor solutions.
This improved the stability and storage time of perovskite precursor solutions, enhanced device repeatability and photoelectric conversion efficiency, simplified the fabrication process and reduced costs, thus promoting the commercialization of perovskite solar cells.
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Figure CN121968991A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of solar cell technology, and in particular to a stable perovskite precursor solution, a perovskite solar cell, and a method for preparing the same. Background Technology
[0002] Perovskite solar cells (PSCs) possess excellent device performance potential and are a photovoltaic technology with great commercial prospects. However, the instability of the perovskite precursor solution, such as precursor aging, can alter core properties of the solution, including colloidal size distribution and chemical composition. This, in turn, affects the film quality of the perovskite thin film, such as grain size, crystallinity, and trapped state density, ultimately leading to significant fluctuations in device performance. The degradation of the precursor solution is driven by multiple complex and difficult-to-monitor chemical processes, including solute-solvent interactions, iodide ion oxidation, deprotonation of halogenated organic salts, and maintaining the consistency of solution chemical composition. As aging time increases, the precursor solution deviates from the ideal stoichiometry, further exacerbating the differences in device performance and hindering the realization of stable, high-performance PSCs.
[0003] Therefore, developing effective strategies to stabilize perovskite precursor solutions is crucial for maintaining the accuracy of solution stoichiometry, ensuring batch-to-batch reproducibility, and ultimately achieving efficient, long-term reliable, and durable PSCs, thus promoting their large-scale commercial application. Summary of the Invention
[0004] In view of this, the purpose of this invention is to provide a stable perovskite precursor solution, a perovskite solar cell, and a method for preparing the same, to solve the problem of easy aging of existing perovskite precursor solutions, which leads to a decline in device performance and reproducibility. This invention utilizes boron-containing compounds as additives to stabilize the halogenated organic salts in the perovskite precursor solution.
[0005] To achieve the above objectives, the present invention provides a stable perovskite precursor solution, wherein the solute of the perovskite precursor solution comprises a perovskite precursor material and a boron atom compound containing empty orbitals, wherein the perovskite precursor material comprises lead halide and a halide organic salt compound, and the molar ratio of halogen atoms in the perovskite precursor material to boron atoms in the boron atom compound containing empty orbitals is 10-200:1.
[0006] Among them, boron-containing compounds interact with halogen anions (such as I) in the precursor solution through the empty outer orbitals of their boron atoms. - This forms a strong interaction, inhibiting the formation of hydroiodic acid (HI), thereby blocking the formation of methylamine cations (MA). + ), formamidinium cation (FA) +The deprotonation process of the perovskite precursor solution stabilizes the precursor solution. The stable perovskite precursor solution developed in this invention has a simple and easy-to-operate preparation process, and the overall cost of raw materials and production is controllable for industrial application. It can overcome the key bottleneck of large-scale production of perovskite solar cells from the core raw material level, providing practical material support for the commercialization of perovskite photovoltaic technology, and possesses outstanding industrial application value and industrialization prospects.
[0007] Optionally, the structural formula of the boron atom compound containing empty orbitals is:
[0008] Or borohydrides;
[0009] Wherein, R1 is one of alkyl, aromatic, or hydroxyl groups; R2 and R3 are one of alkyl, ester, hydroxyl, or halogen groups; and the borohydride is BH3 or BH4. - Salt.
[0010] The molar ratio of lead halide to organic halide is 1:0.9-1.1, the organic halide is at least one of formamidinium iodine, methylamine iodine, and methylamine bromide, and the halogen in the lead halide is one of iodine, chlorine, and bromine.
[0011] This invention provides a method for preparing a stable perovskite precursor solution, comprising the following steps: in a nitrogen-filled glove box, formamidinium iodide, methylamine iodide, lead iodide and a boron-containing compound are dissolved in dimethyl sulfoxide and stirred for 2 hours until completely dissolved.
[0012] The present invention also provides a perovskite solar cell, comprising a perovskite layer prepared from the perovskite precursor solution.
[0013] The present invention also provides a method for preparing the perovskite solar cell, comprising the following steps:
[0014] Step 1: Prepare a metal oxide layer on the substrate;
[0015] Step 2: Spin-coat SAM solution onto the metal oxide layer, and anneal it to form a hole transport layer;
[0016] Step 3: Statically spread the perovskite precursor solution on the hole transport layer, then dynamically spin-coat the perovskite precursor solution, and anneal to form a perovskite layer.
[0017] Step 4: Prepare an electron transport layer on the perovskite layer;
[0018] Step 5: Prepare a hole blocking layer on the electron transport layer;
[0019] Step 6: Deposit Ag as an electrode on the hole blocking layer to prepare a perovskite solar cell.
[0020] In step one, the substrate is ITO glass, which requires pretreatment before use. Specifically, the ITO glass can be ultrasonically treated with deionized water and isopropanol in sequence, then dried with nitrogen and subjected to plasma treatment.
[0021] The metal oxide is nickel oxide (NiO). x The annealing temperature is 130-160℃, and the annealing time is 8-12 min. More preferably, it is 150℃; the corresponding annealing time is 10 min.
[0022] Step one involves preparing a metal oxide layer on a substrate by ultrasonically homogenizing a NiO layer. x The aqueous solution was uniformly spin-coated onto the ITO conductive glass. After annealing, it was naturally cooled to room temperature to obtain a nickel oxide layer.
[0023] Step two involves spin-coating the prepared SAM solution onto the NiOx layer in a nitrogen glove box. After annealing, the solution is cooled to ambient temperature to obtain the hole transport layer.
[0024] In step two, the SAM solution is a carbazole-based phosphate self-assembled monomolecular solution with a concentration of 0.1-5 mg / mL. The spin-coating speed of the SAM solution is 3500-4500 rpm, and the spin-coating time is 25-40 s. The annealing temperature is 90-105℃, and the annealing time is 8-15 min. Preferably, the SAM molecule is MeO-2PACz with a concentration of 0.5 mg / mL.
[0025] The perovskite precursor solution in step three is prepared by dissolving the perovskite precursor material and a boron atom compound containing empty orbitals in dimethyl sulfoxide. Preferably, (25.6 mg) MAI (methylammonium iodide), (199.8 mg) FAI (formamidinium hydroiodate), (690 mg) PbI2 and (13.2 mg) a boron atom compound are dissolved in 1 mL of DMSO and stirred continuously for 2 h until completely dissolved.
[0026] Step 3: In a nitrogen glove box, the prepared perovskite precursor solution is statically spread on the SAM layer. The perovskite film is prepared by injecting antisolvent during the window period using a dynamic spin coating method, thus obtaining the perovskite layer.
[0027] During the spin-coating of the perovskite precursor solution, an antisolvent is added. The spin-coating speed is any value between 5000-6000 rpm, and the spin-coating time is any time between 35-45 s. The antisolvent is added dropwise at any time between approximately 30-35 s during spin-coating. Preferably, the dynamic spin-coating time is 1000 rpm (500 rpm / s acceleration) - 5 s - 6000 rpm (4000 rpm / s acceleration) - 40 s.
[0028] The electron transport layer is a PCBM electron transport layer. Step four involves the following steps: In a nitrogen glove box, the prepared PCBM solution is statically spread onto the perovskite layer, and then spin-coated to obtain the electron transport layer. The PCBM solution concentration is 15-25 mg / mL, and the spin-coating speed is 1800-3000 rpm. More preferably, the concentration is 20 mg / mL, and the spin-coating speed is 2000 rpm.
[0029] The hole-blocking layer is a BCP hole-blocking layer. Step five involves the following steps: In a nitrogen glove box, the prepared BCP solution is statically spread onto the PCBM layer, and then spin-coated to obtain the hole-blocking layer. The BCP solution concentration is saturated, and the spin-coating speed is 3000-6000 rpm. More preferably, the spin-coating speed is 6000 rpm.
[0030] The beneficial effects of this invention are:
[0031] 1. The empty orbitals of the boron atoms in the boron-containing compounds used in this invention can interact with I. - The formation of strong interactions reduces its electron cloud density and suppresses I - Induced MA + Deprotonation improves the stability of the perovskite precursor, thus extending the storage time of the perovskite precursor solution and enhancing device repeatability, which is more beneficial for large-scale production. The stable precursor solution preparation process described in this invention is simple and cost-controllable, effectively promoting the commercialization of perovskite solar cells and possessing extremely high industrial application value.
[0032] 2. The hydroxyl groups in the boron-containing compounds used in this invention and MA + / FA + The NH forms hydrogen bonds, providing double protection for the haloorganic salt and preventing it from undergoing condensation reactions with other components; this is superior to forming films with fewer defects, improving the crystal quality of the film, and further enhancing the photoelectric conversion efficiency and stability of the device. Attached Figure Description
[0033] To more clearly illustrate the technical solutions in this invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only for this invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.
[0034] Figure 1 (a) Color change of the perovskite precursor solution without added triethylene borate in Comparative Example 1 as the standing time increases; Figure 1 (b) Color change of the perovskite precursor solution with added triethylene glycol borate in Example 1 as the standing time increases;
[0035] Figure 2 (a) The 1H NMR spectrum characterization of the perovskite precursor solution without added triethylene borate in Comparative Example 1 at different stages of storage time. Figure 2 (b) The 1H NMR spectrum characterization of the perovskite precursor solution with added triethylene glycol borate in Example 1 at different stages of storage time;
[0036] Figure 3 (a) The device efficiency of the perovskite solar cell in Comparative Example 1 with the addition of triethylene glycol borate as a result of storage time. Figure 3 (b) The device efficiency of the perovskite solar cell with the perovskite precursor solution containing triethylene glycol borate added in Example 1 changes with storage time. Detailed Implementation
[0037] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments.
[0038] It should be noted that, unless otherwise defined, the technical or scientific terms used in this invention should have the ordinary meaning understood by one of ordinary skill in the art to which this invention pertains. Terms such as "comprising" or "including" mean that the element or object preceding the word encompasses the elements or objects listed following the word and their equivalents, without excluding other elements or objects.
[0039] Example 1
[0040] 1. Synthesis of triethylene glycol borate
[0041]
[0042] Dry ethylene glycol (30 mmol, 1.9 g) was added to a 500 mL three-necked round-bottom flask. 50 mL of dichloromethane was added as a solvent. After purging the system with high-purity nitrogen three times, the temperature was lowered to 0–5 °C in an ice bath. Then, anhydrous boron trichloride (10 mmol, 1.2 g) was gradually added dropwise, controlling the dropping rate to maintain the system temperature at 0–10 °C for approximately 2 hours. After the addition was complete, the ice bath was removed, and the temperature was raised to room temperature for 2 hours. After the reaction was complete, 25 mL of saturated sodium chloride aqueous solution was slowly added to quench the reaction. After stirring for 10 minutes, the mixture was transferred to a separatory funnel, allowed to stand for separation, and filtered to remove insoluble matter, yielding a filtrate. The organic phase of the filtrate was dried with anhydrous sodium sulfate for 12 hours, filtered to remove the drying agent, and the solvent was removed by vacuum distillation. The remaining viscous liquid was washed with water multiple times to remove impurities, yielding the crude product of the reaction. Finally, the crude product was dried under vacuum at 60 °C for 12 hours.
[0043] 2. Preparation of perovskite precursor solution
[0044] In this embodiment, the additive is triethylene glycol borate;
[0045] The perovskite precursor raw materials were MAI, FAI and PbI2. The precursor solution was prepared by dissolving (25.6 mg) MAI, (199.8 mg) FAI, (690 mg) PbI2 and (13.2 mg) triethylene glycol borate in 1 mL DMSO and stirring continuously for 2 h. The prepared perovskite solution was then placed in a nitrogen atmosphere in the dark for 1 day, 3 days, 5 days and 7 days respectively.
[0046] Example 2
[0047] 1. Preparation of perovskite solar cells with a precursor solution containing triethylene glycol borate.
[0048] 1) Fabrication of a hole transport layer
[0049] In a glove box (oxygen level ≤ 0.01 ppm), accurately weigh 10 mg of nickel oxide powder into a reagent bottle. Outside the glove box, add 1 mL of deionized water to prepare a 10 mg / mL nickel oxide solution. Seal the bottle opening with a sealing tape and sonicate under running water for 10 min. Under air conditions, spread the filtered nickel oxide solution (using a 0.22 μm polysulfone aqueous filter) onto a substrate. Spin-coat at 3000 rpm (1000 rpm / s acceleration) for 30 s. Place the substrate on a hot plate and anneal at 150 °C for 10 min to prepare a nickel oxide layer. After cooling, transfer the substrate to the glove box. In a glove box (oxygen value ≤ 0.01 ppm), a 0.5 mg / mL MeO-2PACz solution (solvent is anhydrous ethanol) was prepared. The SAM solution after filtration (PTFE 0.22 micron hydrophobic filter) was coated onto the nickel oxide layer and spin-coated at 4000 rpm (2000 rpm / s acceleration) for 30 s. The coating was then placed on a hot table and annealed at 100 °C for 10 min to obtain the SAM layer.
[0050] 2) Preparation of perovskite layer
[0051] ① Preparation of precursor solution: Dissolve (25.6 mg) MAI, (199.8 mg) FAI, (690 mg) PbI2 and (13.2 mg) triethylene glycol borate in 1 mL DMSO, stir continuously for 2 h, and then filter (PTFE 0.22 μm hydrophobic filter) for later use; (passivating agent is 1-butyl-3-methylimidazolium tetrafluoroborate, solvent DMF, concentration 20 mg / mL, 40 uL added); Place the prepared perovskite solution in a nitrogen atmosphere in the dark for 1 day, 3 days, 5 days and 7 days respectively.
[0052] Repeat the following steps for different number of days the perovskite precursor solution was incubated:
[0053] ② In a glove box (water oxygen value ≤ 0.01 ppm), the filtered precursor solution was coated onto the SAM layer. A multi-step spin coating program was used: 1000 rpm (500 rpm / s acceleration) - 5 s - 6000 rpm (4000 rpm / s acceleration) - 40 s for dynamic spin coating of perovskite. At the end of the total time of 32 s, 160 μL of CB antisolvent was rapidly added to obtain a liquid film. After the program was completed, the film was placed on a hot stage and annealed at 100 °C for 20 min to obtain a perovskite film with a thickness of about 450 nm.
[0054] 3) Fabrication of electron transport layer
[0055] ① In a glove box (oxygen level ≤ 0.01 ppm), accurately weigh 20 mg of PC. 61BM was dissolved in 1 mL of chlorobenzene to prepare a 20 mg / mL PCBM solution. The solution was stirred until homogeneous and then filtered for later use.
[0056] ② The above solution was spin-coated onto the surface of the interface passivation layer at a rotation speed of 2000 rpm (1500 rpm / s acceleration) for 40 s to prepare the electron transport layer.
[0057] 4) Preparation of hole blocking layer
[0058] ① In a glove box (oxygen value ≤ 0.01 ppm), accurately weigh 0.5 mg BCP and dissolve it in 1 mL IPA to prepare a 0.5 mg / mL BCP solution. Stir well and filter for later use.
[0059] ② The above solution was spin-coated onto the surface of the electron transport layer at a rotation speed of 6000 rpm (3000 rpm / s acceleration) for 30 s to prepare a hole blocking layer.
[0060] 5) Preparation of Ag electrode
[0061] Using a vacuum evaporation device, 100 nm Ag was deposited on a hole-blocking layer as an electrode, and a perovskite solar cell was finally prepared.
[0062] Comparative Example 1
[0063] In this comparative example, the perovskite precursor raw materials were MAI, FAI and PbI2. The precursor solution was prepared by dissolving (25.6 mg) MAI, (199.8 mg) FAI and (690 mg) PbI2 in 1 mL DMSO and stirring continuously for 2 h. The prepared perovskite solution was then placed in a nitrogen atmosphere in the dark for 1 day, 3 days, 5 days and 7 days respectively.
[0064] Depend on Figure 2 As shown by the 1H NMR spectrum, Comparative Example 1 produced small organic molecule products such as MFAI / DMFAI as the storage time increased, while Example 1 showed better storage stability and almost no cation deprotonation.
[0065] Comparative Example 2
[0066] Fabrication of perovskite solar cells using a precursor solution without added triethylene glycol borate.
[0067] 1) Fabrication of a hole transport layer
[0068] In a glove box (oxygen level ≤ 0.01 ppm), accurately weigh 10 mg of nickel oxide powder into a reagent bottle. Outside the glove box, add 1 mL of deionized water to prepare a 10 mg / mL nickel oxide solution. Seal the bottle opening with a sealing tape and sonicate under running water for 10 min. Under air conditions, spread the filtered nickel oxide solution (using a 0.22 μm polysulfone aqueous filter) onto a substrate. Spin-coat at 3000 rpm (1000 rpm / s acceleration) for 30 s. Anneal at 150 °C for 10 min on a hot plate to prepare a nickel oxide layer. After cooling, transfer the substrate to the glove box. In a glove box (oxygen value ≤ 0.01 ppm), a 0.5 mg / mL MeO-2PACz solution (solvent: anhydrous ethanol) was prepared. The SAM solution after filtration (PTFE 0.22 μm hydrophobic filter) was coated onto the nickel oxide layer and spin-coated at 4000 rpm (2000 rpm / s acceleration) for 30 s. The coating was then placed on a hot table and annealed at 100 °C for 10 min to obtain the SAM layer.
[0069] 2) Preparation of perovskite layer
[0070] ① Preparation of precursor solution: Dissolve (25.6 mg) MAI, (199.8 mg) FAI, and (690 mg) PbI2 in 1 mL DMSO, stir continuously for 2 h, and then filter (PTFE 0.22 μm hydrophobic filter) for later use; (passivating agent is 1-butyl-3-methylimidazolium tetrafluoroborate, solvent DMF, concentration 20 mg / mL, 40 μL added); Place the prepared perovskite solution in a nitrogen atmosphere in the dark for 1 day, 3 days, 5 days, and 7 days respectively.
[0071] Repeat the following steps for different number of days the perovskite precursor solution was incubated:
[0072] ② In a glove box (water oxygen value ≤ 0.01 ppm), the filtered precursor solution was coated onto the SAM layer. A multi-step spin coating program was used: 1000 rpm (500 rpm / s acceleration) - 5 s - 6000 rpm (4000 rpm / s acceleration) - 40 s for dynamic spin coating of perovskite. At the end of the total time of 32 s, 160 μL of CB antisolvent was rapidly added to obtain a liquid film. After the program was completed, the film was placed on a hot stage and annealed at 100 °C for 20 min to obtain a perovskite film with a thickness of about 450 nm.
[0073] 3) Fabrication of electron transport layer
[0074] ① In a glove box (oxygen level ≤ 0.01 ppm), accurately weigh 20 mg of PC. 61 BM was dissolved in 1 mL of chlorobenzene to prepare a 20 mg / mL PCBM solution. The solution was stirred until homogeneous and then filtered for later use.
[0075] ② The above solution was spin-coated onto the surface of the interface passivation layer at a rotation speed of 2000 rpm (1500 rpm / s acceleration) for 40 s to prepare the electron transport layer.
[0076] 4) Preparation of hole blocking layer
[0077] ① In a glove box (oxygen value ≤ 0.01 ppm), accurately weigh 0.5 mg BCP and dissolve it in 1 mL IPA to prepare a 0.5 mg / mL BCP solution. Stir well and filter for later use.
[0078] ② The above solution was spin-coated onto the surface of the electron transport layer at a rotation speed of 6000 rpm (3000 rpm / s acceleration) for 30 s to prepare a hole blocking layer.
[0079] 5) Preparation of Ag electrode
[0080] Using a vacuum evaporation device, 100 nm Ag was deposited on a hole-blocking layer as an electrode, and a perovskite solar cell was finally prepared.
[0081] The performance of the prepared perovskite solar cells was tested by [the following method / organization]. Figure 3 As shown, compared with Example 2, the precursor solution of Comparative Example 2 has worse storage stability. As the storage time of the perovskite precursor solution is extended, the photoelectric efficiency of Comparative Example 2 decreases significantly, while the photoelectric efficiency of Example 2 remains almost unchanged.
[0082] Those skilled in the art should understand that the discussion of any of the above embodiments is merely exemplary and is not intended to imply that the scope of the invention is limited to these examples; within the framework of the invention, the technical features of the above embodiments or different embodiments can also be combined, the steps can be implemented in any order, and there are many other variations of the different aspects of the invention as described above, which are not provided in detail for the sake of brevity. Any omissions, modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the invention should be included within the scope of protection of the invention.
Claims
1. A stable perovskite precursor solution, characterized in that, The solute in the perovskite precursor solution includes a perovskite precursor material and a boron atom compound containing empty orbitals. The perovskite precursor material includes lead halide and organic halide compounds. The molar ratio of halogen atoms in the perovskite precursor material to boron atoms in the boron atom compound containing empty orbitals is 10-200:
1.
2. The stable perovskite precursor solution according to claim 1, characterized in that, The structural formula of the boron atom compound containing empty orbitals is: Or borohydrides; Wherein, R1 is one of alkyl, aromatic or hydroxyl groups; R2 and R3 are one of alkyl, ester, hydroxyl or halogen groups; and the boron hydride is BH3 or BH4. - Salt.
3. The stable perovskite precursor solution according to claim 1 or 2, characterized in that, The molar ratio of lead halide to organic halide is 1:0.9-1.1, the organic halide is at least one of formamidinium iodine, methylamine iodine, and methylamine bromide, and the halogen in the lead halide is one or more of iodine, chlorine, and bromine.
4. A perovskite solar cell, characterized in that, The perovskite layer is prepared from the perovskite precursor solution according to any one of claims 1-3.
5. The method for preparing a perovskite solar cell according to claim 4, characterized in that, Includes the following steps: Step 1: Prepare a metal oxide layer on the substrate; Step 2: Spin-coat SAM solution onto the metal oxide layer, and anneal it to form a hole transport layer; Step 3: Statically spread the perovskite precursor solution on the hole transport layer, then dynamically spin-coat the perovskite precursor solution, and anneal to form a perovskite layer. Step 4: Prepare an electron transport layer on the perovskite layer; Step 5: Prepare a hole blocking layer on the electron transport layer; Step 6: Deposit Ag as an electrode on the hole blocking layer to prepare a perovskite solar cell.
6. The method for preparing a perovskite solar cell according to claim 5, characterized in that, The metal oxide is nickel oxide, and the annealing temperature is 130-160℃, with an annealing time of 8-12 minutes.
7. The method for preparing a perovskite solar cell according to claim 5, characterized in that, In step two, the SAM solution is a phosphate self-assembled monomolecular solution based on the carbazole structure with a concentration of 0.1-5 mg / mL. The spin-coating speed of the SAM solution is 3500-4500 rpm and the spin-coating time is 25-40 s. The annealing temperature is 90-105℃ and the annealing time is 8-15 min.
8. The method for preparing a perovskite solar cell according to claim 5, characterized in that, The perovskite precursor solution in step three is prepared by dissolving the perovskite precursor material and a boron atom compound containing empty orbitals in dimethyl sulfoxide.
9. The method for preparing a perovskite solar cell according to claim 5, characterized in that, An antisolvent is added during the spin coating of the perovskite precursor solution. The spin coating speed is 5000-6000 rpm and the spin coating time is 35-45 s. The antisolvent is added dropwise at any time between 30-35 s during the spin coating process.
10. The method for preparing a perovskite solar cell according to claim 5, characterized in that, The electron transport layer is a PCBM electron transport layer, and the hole blocking layer is a BCP hole blocking layer.