Phase Distribution Regulated By Nanoimprint For Low-dimensional Perovskite And Photovoltaic Device

In recent years,perovskite solar cells(PSCs)have received great attention because of their excellent photoelectric conversion efficiency,high absorption coefficient,adjustable band gap,large carrier diffusion length and relatively low material cost.Although the tradition three-dimensional(3D)PSCs exhibit high efficiency,the 3D perovskite is not stable,which limits the commercial development.Compared to 3D perovskites,two-dimensional(2D)perovskites contain larger,less volatile,and more hydrophobic organic cations and therefore possess better thermal,chemical,and environmental stability.2D perovskites become more promising for photovoltaics and 2D perovskites can play different roles in solar cells,either as a simple light absorbing layer(2D perovskite solar cells)or as a capping layer over the3 D perovskite absorber layer(2D/3D perovskite solar cells).At the same time,2D perovskites also face many challenges.For example,the introduction of large insulating cations complicates the crystallization process and makes the crystallization process susceptible to environmental disturbances,which leads to more defects in the crystallization of 2D perovskites,such as the generally small grains and the pinholes of film.Moreover,the disorder distribution of large insulating cations hinders charge transfer inside the devices,which leads to the degradation of device performance.In this study,the nanoimprinting technique assisted by methylamine acetate was used to improve the quality of perovskite films,optimize the phase distribution inside the films,and enhance the charge transfer.Specifically,with the assistance of methylamine acetate,the imprinting promoted the dispersion of spacer cations in the recrystallization process,which suppressed the formation of low-n phases caused by the aggregation of spacer cations and promoted the formation of 3d-like phases.The prepared perovskite devices exhibit a photovoltaic conversion efficiency of 18.96%with an open-circuit voltage of 1.10 V and a fill factor of 77.20%,and they also show improved humidity and thermal stability.This method provides a simple and effective strategy for obtaining a uniform phase distribution of 2D perovskites.During the high temperature and long-time imprinting process,the perovskite film shows bare lead iodide on the surface,which will be harmful to the charge transfer at the interface.In order to solve this problem,large organic cation is used to treat the surface of the imprinted perovskite film to transfer bare lead iodide to 2D perovskite,bringing a more stable interface.The treated devices exhibit better device performance and stability,with a final photovoltaic conversion efficiency of 20.6%,an open-circuit voltage of 1.12 V,and a fill factor of 75%.This work provides an effective strategy for the development of 2D perovskites.