Molecular Orientation-Steric Hindrance Tradeoff of Cyclohexylammonium Passivators for High-Performance Perovskite Solar Cells

Abstract

Perovskite solar cells (PSCs) have garnered increasing attention and undergone rapid development over the past decade. Nevertheless, efficiency losses and device degradation caused by defects continue to pose significant challenges to the commercialization of PSCs. In particular, the interfaces of solution-processed polycrystalline perovskite films contain numerous defects that need to be passivated to reduce their negative impact. Here, we employ structurally rigid cyclohexylammonium salts with four different chain lengths to passivate the surface defects of perovskite and to elucidate the passivation effects related to molecular orientation and steric hindrance. Among the four passivators, cyclohexylethylammonium iodide (CEAI) provide minimal steric hindrance, resulting in an almost vertical intercalation of CEA + into the inorganic octahedral framework. This configuration favors the strongest passivation effect, thereby suppressing non-radiative recombination and enhancing structural stability. Furthermore, the CEAI-modified perovskite films demonstrate well-matched energy level alignment with the hole transport layer, which facilitates interfacial charge transport and reduces energy loss. Consequently, the conventional n-i-p PSC devices achieve a dramatic efficiency improvement from 23.11% to 25.58% (certified 25.30%). Unencapsulated devices maintain 94.4% of their initial efficiency after 1000 hours of continuous AM 1.5G illumination and retain 92.5% of their original efficiency after 1000 hours of storage in an environment with 35% humidity.