Controlled Crystallization of CsRb‐Based Multi‐Cation Perovskite Using a Blended Sequential Process for High‐Performance Solar Cells

Abstract

High‐quality perovskite films with low defect densities and high carrier‐diffusion lengths are essential for high‐performance perovskite devices. Herein, a modified two‐step sequential method is proposed, in which equal amounts of Cs+ and Rb+ ions (Cs+Rb+) are added to a PbI2 solution in the first step of perovskite deposition. The incorporation of Cs+Rb+ results in trace amounts of δ‐CsPbI3, leading to a reduction in the grain size in the PbI2 layer that facilitates better penetration of the organic salts in the second step of the precursor deposition. Meanwhile, the low density of the δ‐CsPbI3 crystals act as seeds to regulate the nucleation and growth of the perovskite crystals. A single‐layered columnar large‐grain perovskite film is obtained. The addition of Cs+Rb+ promotes crystal growth along the (100) orientation, which is beneficial for the reduction of surface defects. The incorporated Rb+ ions can regulate the remaining PbI2 in the perovskite. The improved quality of the perovskite film results in a significantly prolonged carrier lifetime of ≈7.01 and an enhanced electron diffusion length of ≈2.84 . As a result, the photovoltaic parameters are all improved in the established devices and a power conversion efficiency of 21.49% is reached.