Abstract
Tin is a valuable candidate for replacing lead in perovskites solar cells. Tin oxidation, however, strongly limits the efficiency and the long-term stability of tin halide perovskites (THP) in devices. To mitigate this issue, capping 3D THP with analogue 2D perovskites through the addition of large cations is an emerging strategy, leading to increased performance and stability. In this study, based on the state of the art density functional theory calculations, the possible beneficial effects of large cations (BA, PEA, and AVA) on the tin stability at the surface is investigated. Our results show that large cation dipoles of the 2D perovskites modulate tin oxidation potential at the surface of 3D perovskites by hindering the formation of tin vacancies and the degradation of the material. This study confirms that stabilization of tin at the surface is key for the full exploitation of THP in long-term stable devices.