Brownian Tree?Shaped Dendrites in Quasi?2D Perovskite Films and Their Impact on Photovoltaic Performance

Quasi-2D Ruddlesden–Popper perovskites (RPPs) are candidates for constructing perovskite solar cells (PSCs) with superior stability due to their tolerance the external environment. Fully understanding film growth mechanism and structure is crucial further improve performance of 2D-PSCs while maintaining device stability. In this work, origin Brownian tree-shaped dendrites formed in hot-cast methylammonium chloride (MACl)-doped BA2MAn?1PbnI3n+1 ( = 5) quasi-2D films reported. Investigations based on optical, electronic, atomic force, fluorescence microscopies reveal that assembled from large-n RPPs-dominated grains, nondendritic area composed small-n RPPs grains associated surface pits caused by evaporation MACl. It proposed these grown diffusion-limited aggregation MA-rich intermediate phase domains initially crystallize precursor. The formation upon MACl doping accompanied improved organization crystallinity 2D RPPs, which benefits photovoltaic performance. This work provides new insights into should assist engineering strategies PSCs.