Research On Interface Modification Of Perovskite Solar Cells Using Quaternary Ammonium Salts

Organic-inorganic hybrid perovskite materials have the advantages of high carrier mobility,low exciton binding energy,high extinction coefficient and adjustable bandgap,which can be used as efficient light absorbing layers for solar cells.Since the first report in 2009,the power conversion efficiency（PCE）of perovskite solar cells（PSCs）has been continuously improved,and the highest reported efficiency has reached 25.7%.However,the stability issue is one of the key issues restricting the further development of PSCs.The use of interfacial engineering strategies to passivate perovskite surface defects and enhance the water and oxygen resistance of perovskite layers has become a common method to improve the efficiency and stability of PSCs.However,how to choose suitable interface materials to improve the interface microstructure and electrical properties is crucial to improve device efficiency and stability.Therefore,in this paper,the low-dimensional（LD）perovskite interface layer was prepared by post-treatment of quaternary ammonium salt,and the microstructure and electrical properties of the low-dimensional perovskite interface layer were optimized by constructing polymer-modified double interface layer and selecting quaternary ammonium salts with different molecular structures to improve the efficiency and stability of carbon-based PSCs based on planar structure.The specific research contents are as follows:（1）The growth process of the one-dimensional（1D）perovskite interface layer is regulated by the p-type polymer semiconductor layer,and the polymer/1D perovskite double interface layer structure is constructed,which improves the microstructure and electrical properties of the perovskite interface layer.The quaternary ammonium salt tetrabutylammonium iodide（TBAI）was used as the post-processing material,which can interact with the excess lead iodide（Pb I₂）on the perovskite surface to form 1D perovskite.However,the morphology of 1D perovskite interface layer is not controllable because Pb I₂ tends to form large-size agglomerates.Therefore,we used poly[[4,8-bis[（2-ethylhexyl）oxy]benzo[1,2-b:4,5-b’]dithiophene-2,6-diyl][3-fluoro-2-[（2-ethylhexyl）carbonyl]thieno[3,4-b]thiophenediy（PTB7）polymer for antisolvent treatment of perovskite films.PTB7 was found to regulate the growth process of 1D perovskite and form a smoother and flatter1D perovskite interface layer on the perovskite surface.The 1D perovskite interfacial layer prepared by this method helps to passivate the surface defects of perovskite,while significantly improves the charge transport at the interface charge.The PCE for carbon-based PSC modified by the PTB7/TBAI interface was increased from the initial 15.11%to 17.03%.In addition,the PTB7/TBAI interface-modified device exhibited significantly improved stability,which maintained more than 80%of the initial PCE after 528 h under damp heat conditions.（2）The effect of quaternary ammonium salts with short alkane chains and asymmetric structures on interfacial properties of the low-dimensional perovskites was investigated.By selecting the quaternary ammonium salt ethyltripropylammonium iodide（EPAI）as the interface modification material,the reaction rate of EPAI with excess Pb I₂ slowed down to form a flatter and smoother low-dimensional perovskite interface.At the same time,the EPAI passivated the surface defects of the perovskite and improved the water and oxygen resistance of the perovskite film.Besides,the short chain of EPAI helps to improve the electrical properties of the perovskite interlayer and promote the interfacial charge transfer.Thus,the carbon-based PSC with EPAI interface modification achieved a PCE of 17.81%and exhibited lower hysteresis.In addition,the stability of the EPAI modified device under high humidity was significantly enhanced,and the unencapsulated device maintained 97.09%of the initial PCE after 1152 h storage at 70-80%relative humidity.（3）The aromatic quaternary ammonium salt phenyltrimethylammonium iodide（PTAI）was studied to improve the phase stability of formamidine lead iodide perovskite（FAPb I₃）and improved performance and stability of FAPb I₃ perovskite solar cells.The research results show that PTAI molecules containing benzene rings can interact with excess Pb I₂ on the surface of perovskite to form low-dimensional perovskite layer,which which can enhance the hydrophobicity and phase stability of the films,and improve the surface morphology of the film.PTAI can also reduce the defects on the surface of perovskite films and inhibit the nonradiative recombination of perovskite films.As a result,the PCE of the PTAI-modified carbon-based PSC was increased from 16.17%to18.06%,and the hysteresis effect of the device was significantly reduced.In addition,the PTAI-modified device exhibited high humidity stability,which maintained the 93.20%of the initial PCE after 30 days in air with a humidity of 40-50%.