Origin of Enhanced Nonradiative Carrier Recombination Induced by Oxygen in Hybrid Sn Perovskite.

Oxygen ingression has been shown to substantially decrease the carrier lifetime of Sn-based perovskites, behind which the mechanism remains yet unknown. Our first-principles calculations reveal that in prototypical MASnI 3 (MA = CH 3 NH 3 ), oxygen by itself is not a recombination center. Instead, it tends to form substitutional O I through combining with native I vacancies (V I ) and remarkably increases the original recombination rate of V I by 2-3 orders of magnitude. This rationalizes the experimentally observed sharp decline of carrier lifetime in perovskites exposed to air. The significantly enhanced carrier recombination is due to a smaller electron capture barrier of O I , resulting from lattice strengthening and the suppressed structural relaxation upon electron capture. These insights offer a route to further improve device performance via anion engineering in broad Sn-based perovskite optoelectronics operating in ambient air. Moreover, our results highlight the important role of lattice relaxation for nonradiative carrier capture in materials in general.