Competition Between Controllable Non-Radiative and Intrinsic Radiative Second-Order Recombination in Halide Perovskites

TL;DR

This study investigates the second-order non-radiative recombination pathway in halide perovskites, revealing its extrinsic nature and surface state origin, which impacts solar cell efficiency and requires targeted mitigation strategies.

Contribution

It identifies the origin of second-order non-radiative recombination as surface states and distinguishes it from intrinsic processes, guiding improved device optimization.

Findings

Second-order recombination depends on extrinsic factors.

Shallow surface states are primary origin of second-order non-radiative losses.

Mitigation strategies must target each recombination type separately.

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. Whilst the most widely known non-radiative recombination from solar cells relates to carrier trapping and is first order in carrier density, recent reports have revealed a non-radiative pathway that is second order. However, the origin and impact of this second-order process on devices remain unclear. Here, we understand this non-radiative second-order recombination (k2non) pathway by manipulating the charge carrier dynamics via controlling the bulk and surface conditions. By combining temperature-dependent spectroscopies, we demonstrate that the value of k2non depends on extrinsic factors, in contrast to intrinsic second-order recombination, which aligns with theoretical evaluations through van Roosbroeck-Shockley relations. Based on density functional theory simulations and Quasi-Fermi level calculations, we propose that shallow surface states are the primary origin of this second-order non-radiative component, contributing up to ~80 mV of the overall reduction in Voc at room temperature. This work reveals that 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.