Gradient Energy Alignment Engineering for Planar Perovskite Solar Cells with Efficiency Over 23%

Abstract An electron‐transport layer (ETL) with appropriate energy alignment and enhanced charge transfer is critical for perovskite solar cells (PSCs). However, interfacial energy level mismatch limits the electrical performance of PSCs, particularly the open‐circuit voltage ( V OC ). Herein, a simple low‐temperature‐processed In 2 O 3 /SnO 2 bilayer ETL is developed and used for fabricating a new PSC device. The presence of In 2 O 3 results in uniform, compact, and low‐trap‐density perovskite films. Moreover, the conduction band of In 2 O 3 is shallower than that of Sn‐doped In 2 O 3 (ITO), enhancing the charge transfer from perovskite to ETL, thus minimizing V OC loss at the perovskite and ETL interface. A planar PSC with a power conversion efficiency of 23.24% (certified efficiency of 22.54%) is obtained. A high V OC of 1.17 V is achieved with the potential loss at only 0.36 V. In contrast, devices based on single SnO 2 layers achieve 21.42% efficiency with a V OC of 1.13 V. In addition, the new device maintains 97.5% initial efficiency after 80 d in N 2 without encapsulation and retains 91% of its initial efficiency after 180 h under 1 sun continuous illumination. The results demonstrate and pave the way for the development of efficient photovoltaic devices.