Space-limited Growth Strategy Of CH₃NH₃PBI₃-based Perovskite Layer And Applications In Photovoltaic Devices

The organic-inorganic metal halide perovskite semiconductors have recently attracted extensive attentions due to their outstanding photoelectric characteristics,such as adjustable bandgap,high absorption coefficient,long carrier diffusion length,and high defect tolerance.Up to now,metal halide perovskite solar cells（PSCs）have achieved rapid development in power conversion efficiency（PCE）up to 25.7%and long-term stability.The crystal morphologies and film properties of perovskite are crucial for the construction of efficient carrier transport channels.However,the unbalanced thermodynamic crystallization process originating from the intrinsic ionic nature of perovskite results in the formation of inferior perovskite films with coarse surface,pinholes,partially random crystal orientation,and tremendous electron defects.These issues will adversely impact the efficiency and environmental stability,thereby hindering commercialization of PSCs.To improve the crystallization quality of perovskite film,tremendous approaches have been developed towards modulating the crystallization kinetic of perovskite.However,these strategies including additive engineering,solvent engineering and optimized thermal annealing treatment are difficult to simultaneously repair both the bulk and surface of perovskite films.Herein,we design a novel space-limited growth strategy to optimize the crystallization process of perovskite film.The limited space is constructed by using polydimethylsiloxane（PDMS）flexible membrane.Given that the multifunctional PDMS membrane used in the space-limited growth strategy is similar to the facial mask for promoting the skin absorption of skincare ingredients,the perovskite space-limited growth process is vividly named as Facial Mask（FM）method.During thermal annealing process,the solvent or solution adsorbed in the PDMS membrane would gradually diffuse into the perovskite-precursor film and form a stable microenvironment for regulating the crystal growth and modulating the surface properties.（1）The development of PDMS membrane assisted space-limited growth strategy and photovoltaic applicationsIn this work,toluene（Tol）,ethyl acetate（EA）and isopropanol（IPA）were adsorbed in PDMS membrane by simple physical immersion.During the annealing process,the solvent adsorbed in PDMS would diffuse into the perovskite layer and facilitate the formation of perovskite crystal nucleuses.The FM-treated perovskite film displays a smooth surface with regular distribution of perovskite grains and improved crystal orientation in vertical direction.In addition,the optimized films show enhanced crystallinity and decreased defect density.Consequently,compare to the control one（18.1%）,the resultant devices deliver an enhanced PCE up to 20.9%（FM-Tol）,20.7%（FM-EA）and 19.7%（FM-IPA）,respectively,and also exhibit improved operation stability.The optimized devices maintain approaching 90%of their initial PCE after 1800 hours self-storage in N₂environment,whereas only 75%of the initial PCE was observed for control device under the identical condition.（2）Passivation effect of organic amine salts based on space-limited growth strategy and photovoltaic applicationsThe PDMS membranes were separately immersed in methylammonium iodide（MAI）/IPA solution and phenethylammonium iodide（PEAI）/IPA solution to regulate crystal growth and modulate interface properties.The developed FM strategy can improve surface morphology,repair electron defect and enhance vertical orientation of（100）plane,thus constructing efficient carrier transport channel for high-performance PSCs.Meanwhile,the PEAI-adsorbing FM results in PEA⁺terminated surface of perovskite film,demonstrating a more n-type surface character for efficient electron extraction at the interface of perovskite/electron transport layer.Consequently,the champion device achieves a remarkably improved PCE from 18.2%（Control）to 21.4%（FM-PEAI）,which is among the highest reported values for MAPb I₃-based PSCs.In addition,the FM-PEAI film exhibits alleviated residual stress and the corresponding device also reveals superior thermal/humidity stability.