Accelerated degradation

Abstract

Perovskite solar cells have demonstrated high power conversion efficiency, yet their stability under realistic conditions remains to be convincingly demonstrated. One critical step in addressing the issue is the development of accelerated ageing tests (that is, use of higher stress levels than in real-world conditions) that can reproduce in the laboratory the failure modes observed in the field. It is crucial to identify the type of stressor and its magnitude, and ensure that the degradation mechanisms induced in the test match those occurring in the field. The tests should also be able to mimic the removal or attenuation of the stressor during day/night and seasonal cycles, capturing reversible and irreversible processes. Now, Mark Khenkin and colleagues across Europe and Israel investigate the application of continuous forward bias in the dark followed by storage in the dark as an acceleration test.

The researchers observe a decrease in the short-circuit current and shunt resistance (which opposes undesired current pathways bypassing the main circuit) under forward bias, with recovery during dark storage, while the open-circuit voltage shows the opposite trend. They attribute the behaviour to ions migrating to interfaces when forward bias is applied, impeding charge transport, and redistributing during dark storage, leaving defects at the interface that reduce the voltage. Khenkin and team show that this behaviour replicates the seasonal variations in performance of solar cells operating outdoors in Berlin, Germany, over 20 months. The forward-bias step mimics spring and summer behaviour, while dark storage captures autumn and winter operation. The findings provide an example of accelerated ageing tests that can mimic ion migration-induced degradation in the field.