Degradation Dynamics of Perovskite Solar Cells Under Fixed Reverse Current Injection

TL;DR

This study investigates how different hole-transport layers affect the degradation pathways of perovskite solar cells under fixed reverse-current stress, revealing distinct failure modes and the importance of charge-mediated electrochemical degradation.

Contribution

It introduces a novel focus on constant reverse-current stress in perovskite solar cells and compares degradation mechanisms based on hole-transport layer choice.

Findings

PTAA layers lead to catastrophic breakdown under high reverse current.

MeO-2PACz layers show gradual, recoverable degradation.

Lower currents over longer durations cause more severe degradation.

Abstract

Previous studies of reverse-bias stability in perovskite solar cells have focused primarily on voltage controlled reverse-bias tests. Here we instead present an investigation of perovskite solar cell degradation under well-defined, constant reverse-current stress. We show that the choice of hole-transport layer dictates the dominant degradation pathway: cells using thick poly(triphenylamine) (PTAA) layers with better indium-doped tin oxide (ITO) coverage can tolerate high reverse bias but quickly undergo catastrophic breakdown under fixed reverse current near their one-sun maximum power-point. In contrast, cells modified with the phosphonic-acid interface layer MeO-2PACz, with poorer ITO coverage compared to PTAA, exhibit soft, gradual, and largely recoverable degradation, regardless of the shading conditions. For MeO-2PACz devices, degradation increases with both current magnitude and duration. Importantly, when normalized by injected charge (current times duration), lower currents applied over longer times cause more severe degradation than higher currents over shorter periods. Combining electrical measurements with spatially resolved photoluminescence imaging, we argue against shunt formation and instead support an ion- and charge-mediated interfacial electrochemical degradation mode.