Synchronous dimension-crystallization engineering enables highly efficient 2D/3D tin perovskite solar cells

Tin perovskite films with two-dimensional/three-dimensional (2D/3D) heterostructures show promise for high performance lead-free perovskite solar cells (PSCs); however, they face challenges due to the undesirable carrier transport caused by intrinsic multi-quantum wells, and susceptible crystallization kinetics caused by the introduction of organic spacer cations. We herein propose and validate a strategy that could simultaneously address these challenges based on synchronous dimension-crystallization engineering in 2D/3D tin perovskite films. Different from the conventional dimension engineering that relies on precise n-phase control, the employed 4-guanidinium benzoate hydrochloride (GBAC) in the present work has an unforeseen desorption effect between phenylethylamine (PEA) and the perovskite, which leads to a direct transition from the 2D to the 3D phase. It is also found that introducing GBAC results in the formation of elongated organic-inorganic hybrid chains, which improves the crystallization process of the films by accelerating both nucleation and growth rates. By virtue of these merits, the resulting tin PSCs achieve a champion power conversion efficiency of 15.02%, together with exceptional long-term stability with 87% remaining after 4000 h and 80% after 400 h under working at the maximum power point.