Air-Processed\nEfficient Cesium-Based Two-Dimensional\nPerovskite Solar Cells Based on Asymmetric Chiral Ammonium Salts

Cesium-based\ntwo-dimensional (2D) perovskites with attractive phase\nand environmental stability have broad application prospects in single-junction\nand tandem perovskite solar cells (PSCs). However, the severe nonradiative\nrecombination and significant energy losses due to disordered phase\norientations and phase distributions greatly hinder the carrier transport\nperformance of cesium-based 2D PSCs and severely limit their photovoltaic\nperformance. Here, we employ an asymmetric chiral spacer cation source,\n(<i>R</i>)-α-phenylethylamine acrylate (<i>R</i>-α-PEAAA), to prepare high-quality 2D cesium-based films with\nuniform phase distribution and high out-of-plane orientation by air\nprocessing, resulting in efficient carrier transport. More importantly,\nthe asymmetric chiral spacer <i>R</i>-α-PEA has a\nstronger dipole moment than its isomer (PEA), which can regulate the\ndielectric properties of cesium-based 2D perovskites and promote charge\ndissociation. In addition, the chiral <i>R</i>-α-PEA\ncan optimize the morphology and out-of-plane orientation of perovskite\nfilms, reduce trap density and nonradiative recombination loss, and\noptimize energy level alignment, thus enhancing carrier transport.\nAs a result, cesium-based 2D PSCs (<i>R</i>-α-PEA<sub>2</sub>Cs<sub>4</sub>Pb<sub>5</sub>I<sub>16</sub>, <i>n</i> = 5) achieved a record power conversion efficiency of 19.71% and\nthe unencapsulated device maintained over 90% efficiency after 1500\nh of continuous light exposure and ambient storage (35 ± 5% relative\nhumidity). This study provides an idea for the development of chiral\n2D perovskite with efficient charge carrier transport toward efficient\nand stable cesium-based 2D PSCs.