Investigation On Interface Engineering For High-efficiency And Stable Perovskite Solar Cells

The organic-inorganic hybrid perovskite solar cells（PSCs）have been widely researched because of their excellent photoelectric properties and low-cost solution processing.The photoelectric conversion efficiency（PCE）of PSCs has rocked from 3.8%to 25.5%in a few years,showing a huge application prospect.Although the efficiency of PSCs has made great breakthroughs,its maximum certification efficiency is still a gap compared with the theoretical limit.Besides,the stability of PSCs is also an obstacle to its large-scale commercialization.Methods including perovskite component engineering,interface engineering,and new material development have been used to improve the efficiency and stability.This dissertation is mainly focused on the interface engineering method to improve the device efficiency and stability of PSCs with regular planar structure（n-i-p）.The main research content and conclusions of this dissertation include the following parts:（1）Study on the modification of TiO₂/perovskite interface by fullerene derivatives.Two fullerene derivatives(PC₆₁BM and C₆₀-SAM)and their mixtures were used to modify the TiO₂/perovskite interface.The modification of PC₆₁BM and C₆₀-SAM effectively improves the morphology and crystal quality of the perovskite film,reduces the defects density of the interface,and enhances the charge collection and extraction at the TiO₂/perovskite interface.C₆₀-SAM could form chemical bonds with TiO₂,so the arrangement of C₆₀-SAM on the TiO₂ surface is more orderly than PC₆₁BM,which is more conducive to inducing high-quality perovskite film crystallization and improving the interface charge transport.The C₆₀-SAM modified device achieved the highest PCE of 17.8%which is significantly higher than those of the pristine device（12.94%）and PC₆₁BM modified device（16.05%）.The interface modification reduces the defects density of the interface,improves the charge transfer and collection at interface,and suppresses the hysteresis of the device.The C₆₀-SAM modified device shows the smallest hysteresis.In addition,the interface modification could also improve the stability of PSCs.The C₆₀-SAM modified device maintained 95.0%of its initial value after being stored in glovebox for 170 hours,much higher than the pristine device（72.4%）and PC₆₁BM modified device（89.8%）.（2）Study of PSCs based on low-temperature combustion synthesized In₂O₃ electron transport layer（ETL）.The In₂O₃ ETL was prepared by the combustion method and used in PSCs.The study shows that the indium nitrate and acetylacetone in the In₂O₃ precursor solution are used as oxidizer and fuel,respectively.The exothermic reaction during the annealing process reduces the annealing temperature of In₂O₃ film.The effects of annealing temperature on the characterstics of combustion synthesized In₂O₃ films were studied.Due to the exothermic reaction of the combustion method,the In₂O₃ films show obvious crystallization peak when being annealed at 150 ^oC,and the In₂O₃ films also show the highest electron mobility of 0.65 cm²V^-1s^-1 when being annealed at 230 ^oC.The combustion synthesized In₂O₃ ETL shows uniform and flat surface morphology,high electron mobility and good energy level matching with perovskite,which is beneficial to the charge extraction and collection at the In₂O₃/perovskite interface.The PSC based on combustion synthesized In₂O₃ ETL shows the highest PCE of 18.12%which is the highest efficiency of PSCs based on In₂O₃ ETL reported in the same period,and it also shows a small hysteresis.More importantly,In₂O₃ ETL has good stability,and the PSC based on In₂O₃ ETL maintained 75%of its initial value after 120 days’storage in glovebox.（3）Study on charge transfer doping and passivation on the surface of perovskite.FDC-2-5Cl is used to treat the surface of perovskite film.FDC-2-5Cl has a high charge carrier mobility and a good energy level alignment with the perovskite.Moreover,FDC-2-5Cl could interact with elements such as Pb and I on the surface of perovskite to passivate surface defects of perovskite,and improve the surface morphology at the same time.The ultraviolet photoelectron spectroscopy（UPS）test shows that the FDC-2-5Cl treatment induces a p-type doping effect on the surface of perovskite film and leads to the bending of surface energy band of perovskite film,which increases the charge transfer at perovskite/spiro-OMe TAD interface.First-principles calculation shows that FDC-2-5Cl forms Pb-Cl and MA-Cl interactions with the perovskite to passivate surface defects,increases the formation energy of perovskite surface defects,and reduces surface energy of perovskite film.First-principles calculation also proves the charge transfer between perovskite and FDC-2-5Cl.The FDC-2-5Cl treatment significantly increases the open circuit voltage(V_oc)of the PSCs.The PSCs with FDC-2-5Cl treatment shows a maximum PCE of 21.16%with a high V_oc of 1.14 V.In addition,the FDC-2-5Cl treatment significantly improves the hydrophobicity of the perovskite film,thereby improving the stability of the PSCs.The PSCs with FDC-2-5Cl treatment maintained 88%of its initial PCE after being stored in air for 1008 hours.（4）Study of multi-effect synergistic surface defect passivation on perovskite films.The2-Th EABr is used to passivate perovskite film.The research results show that 2-Th EABr has multiple passivation effects.The S on the thiophene group in the 2-Th EABr could form a coordination bond with the undercoordinated Pb²⁺on perovskite surface,and Br^—could fill the halide vacancies and interact with Pb²⁺by forming Br-Pb ionic bond,2-Th EABr could also form two-dimensional perovskite on the surface of perovskite,thereby effectively passivating the surface defects of perovskite film.2-Th EABr passivation significantly improves the V_oc and fill factor（FF）of PSCs.The device based on 2-Th EABr passivation achieves a maximum PCE of 21.13%which is significantly higher than that of the unpassivated device.In addition,2-Th EABr passivation significantly improves the hydrophobicity of the perovskite film,thereby improving the stability of the PSCs.The unencapsulated PSCs stored in air for 1200 hours,the 2-Th EABr passivated PSC maintained 85%of its initial PCE and the 2-Th EABr passivated PSC also maintained 86%of its initial PCE under continuous light after 120 minutes,showing good long-term stability and light stability.