Homogenized Wide Bandgap Perovskites for Photostable and Efficient Four‐Terminal All‐Perovskite Tandem Solar Cells

Abstract Wide bandgap perovskite solar cells (WBG PSCs) have attracted widespread attention owing to their potential application in tandem solar cells. However, the mixed halide WBG perovskites suffer from serious phase segregation issues, which severely restrict the power conversion efficiency (PCE) and stability of the resulted device. Herein, an effective bottom‐up strategy has been developed to stabilize WBG perovskites by incorporating propylammonium chloride (PACl) at the buried interface. The PACl can interact with PbI 2 to form a thin layer of low dimensional perovskites at the perovskite/SnO 2 interface, which enables the formation of an energetic cascade structure to accelerate electron extraction. Moreover, the as generated low dimensional perovskites can seed perovskite growth with homogenized halide distribution and released lattice strain. Owing to the uniformed crystallization, suppressed defect states, and accelerated charge transport, the light induced phase segregation within the WBG perovskite is largely suppressed. As a result, a champion efficiency of ≈20% is obtained in a WBG PSC, and over 90% of the initial efficiency is maintained after 2000 h storage. By combining with a narrow bandgap PSC, a four‐terminal all perovskite tandem solar cell is ultimately constructed with a promising efficiency up to 27.2%.