Hydrophobic long alkyl chain organic cations induced 2D/3D heterojunction for efficient and stable perovskite solar cells

Designing post-formed two-dimensional (2D) perovskite on the surface of three-dimensional (3D) perovskite with matched energy levels and high stability is crucial for improving the performance and stability of perovskite solar cells (PSCs). Herein, a long alkyl chain dodecylammonium bromide (DABr) was applied to react with excessive lead iodide (PbI2) on the grain boundary of metal halide perovskite preferentially, forming DA2PbI4 (n = 1) to constitute a clear 2D/3D heterojunction. The existence of heterojunction increases the intensity of the built-in electric field of the device to enhance carrier separation and extraction, and the amino group of dodecylammonium cation passivates defects, which jointly contribute to the improvement of the power conversion efficiency (PCE) from 20.35 to 21.81%. The long alkyl chain endows the 2D perovskite with good hydrophobic properties, improving the humidity and thermal stability of the device. The unencapsulated device can maintain 64% of its initial efficiency after 1065 h storage in ambient air.