Molecular design of defect passivators for thermally stable metal-halide perovskite films

Summary

Small-molecule-based Lewis base additives have been explored as defect passivators to improve the thermal stability of perovskites. However, the high diffusivity and low molecular weight (M_w) of these additives, along with their low coordination numbers (N_c < 5) with perovskites, often fall short in efficiently stabilizing perovskites under thermal stress. Here, we design and synthesize a set of small molecular passivators with controllable N_c (2–15) and M_w (222.3 g/mol ∼2071.6 g/mol). We systemically investigated how the N_c, M_w, and molecular configuration of the additives impact the morphological and optoelectronic properties and thermal stability of Cs_0.05(FA_0.85MA_0.15)_0.95Pb(I_0.85Br_0.15)₃ perovskite thin films. We find that higher N_c and M_w, when accompanied by a large structural hindrance, can simultaneously improve the grain size and defect passivation, thereby improving the overall optoelectronic properties and thermal stability of perovskites. This study identifies a rational molecular design strategy for small molecular additives in perovskites.