Modulating non-radiative recombination related to shallow traps in halide perovskites

Abstract

Halide perovskite solar cells have demonstrated a rapid increase in power conversion efficiencies. Understanding and mitigating remaining carrier losses in halide perovskites is now crucial to enable further increases to approach their practical efficiency limits. Recent observations in halide perovskites have revealed processes such as shallow carrier trapping, which give rise to an apparent non-radiative bimolecular channel that is difficult to distinguish from intrinsic radiative recombination. Here, we quantify this shallow-trap manifestation by jointly analyzing time-resolved photoluminescence and quantum efficiency to separate the total second-order term into radiative (ηesck2r) and shallow-trap-mediated non-radiative contributions (k2non), and evaluate their device impact. We show that k2non is strongly modulated by temperature and surface chemistry and thus depends on extrinsic factors and its origin is independent from deep traps, whereas the intrinsic radiative coefficient and intrinsic second-order recombination follow detailed-balance expectations and align with theoretical evaluations through van Roosbroeck–Shockley relations. Based on density functional theory simulations and Quasi-Fermi level calculations, we propose that surface states are the primary origin of this shallow-trap-related second-order component, contributing up to ∼80 mV of the overall reduction in Voc at room temperature. This work reveals that the origin of carrier losses from two non-radiative recombination types (first and second order) are not linked, emphasizing the need for distinctive mitigation strategies targeting each type to unlock the full efficiency potential of perovskite solar cells.