Visualising nanoscale bias-induced degradation in halide perovskite solar absorbers

Abstract

Abstract Halide perovskite absorbers show enormous potential for next-generation photovoltaic technologies, yet fundamental material degradation mechanisms under operation remain poorly understood. Here, the operational degradation mechanisms in formamidinium-rich (FA-rich) perovskite solar absorbers are studied at the nanoscale through correlative and in-situ electron microscopy techniques, unveiling a rich interplay between charge-carrier-mediated redox reactions and ion segregation under electrical bias. We observe the formation of a degradation front near the positive contact that we ascribe to iodide oxidation and migration. At the opposite contact we see the effects of lead reduction. Alloyed perovskite compositions exhibit more widespread degradation correlated to the presence of nanoscale defective phases and halide heterogeneity, with the microstructure orientation playing a role in the nucleation of phase impurities, carrier transport and transformation under bias. The multi-electrode design biasing platform employed here uniquely enables the selective decoupling of hole- and electron-mediated degradation processes, allowing direct insights into the response of halide perovskite thin films to electrical bias, and the resulting degradation pathways. This fundamental understanding of the electrochemical behaviour of hybrid absorbers will inform strategies for enhanced stability in perovskite optoelectronic devices.