Cyclohexylammonium‐Based 2D/3D Perovskite Heterojunction with Funnel‐Like Energy Band Alignment for Efficient Solar Cells (23.91%)

Abstract Insufficient charge extraction at the interfaces between light‐absorbing perovskites and charge transporting layers is one of the drawbacks of state‐of‐the‐art perovskite solar cells. Surface treatments and/or interface engineering are necessary to approach the Shockley–Queisser limit. In this work, novel 2D layered perovskites, such as CHA 2 PbI 4 (CHAI = cyclohexylammonium iodide) and CHMA 2 PbI 4 (CHMAI = cyclohexylmethylammonium iodide), are introduced in between 3D perovskites and hole transporting layers by a simple solution process and the 2D/3D perovskite heterojunction is formed and confirmed. Spontaneous photoluminescence quenching is observed by efficient hole extraction with a favorable valence band alignment. The charge extraction ability and recombination are directly measured by the transient photocurrent and photovoltage. Moreover, the interface resistance of the devices significantly is decreased to 30% as compared to devices without 2D perovskites. As a result, the devices with 2D/3D perovskite heterojunction exhibit improved power conversion efficiency (PCE) from 20.41% to 23.91% primarily because of the increased open‐circuit voltage (1.079 to 1.143 V) and fill factor (78.22% to 84.25%). The results provide a detailed insight into hole extraction and high PCEs with the formation of a 2D/3D perovskite heterojunction.