Lead halide perovskites have recently raised as an easy to process and cost-effective photovoltaic material. However, stability issues have to be addressed to meet the market need for 25 years durable technology. The stability of the perovskite itself, as well as the stability of the perovskite embedded in a complete device under real working conditions, are a key challenge for perovskite solar cells.
Within this study, we used Photoconductive Atomic Force Microscopy (pcAFM) and Photoluminescence imaging (PL) to investigate at the nanoscale level the degradation of the perovskite film under light and voltage stress. Then, we correlate the nanoscale pcAFM and PL analysis to the macroscopic device behaviour in similar ageing condition. We found that non-reversible performance losses in a complete device originate from degradation localised at the grain boundaries of the perovskite film. Interesting, within the bulk of the perovskite grains we observed fully reversible behaviours. We conclude that the grain boundaries are detrimental to the device stability and they need to be minimized or passivated to achieve fully stable perovskite solar cells even under anhydrous conditions.