Probing Phase Distribution in 2D Perovskites for Efficient Devices Design.

Two-dimensional (2D) lead halide perovskite has recently been recognized as a promising candidate to stabilize perovskite solar cells due to its extraordinary moisture resistance. These 2D perovskite films often consist multiple phases with layered (n) of lead halide (from n=1,2,3, to ≈∞). However, convincing evidence is still lacking to clarify the phase distribution with respect to different n, thus causes the misleading for device design. Herein, the confocal photoluminescence (PL) spectroscopy was applied to probe the inhomogeneity of 2D perovskite films along the vertical direction to construct a clear phase distribution mapping consequently. It reveals that the 2D perovskite phases (n=2,3,4) locate preferentially near the substrate, while large n phases are predominant near the top surface. Moreover, we successfully developed a simple method to manipulate the phase distribution in 2D perovskites thin films, which results in a dramatic increase of device efficiency from 4.95% to 11.6%. Our findings thus provide insights to the understanding of 2D perovskite film growth. The utilization of visualized phase distribution data could also guide the further development of 2D perovskite materials for optoelectronic devices.