Morphological Insights into the Degradation of Perovskite Solar Cells under Light and Humidity

Perovskite solar cells (PSCs) have achieved competitivepower conversionefficiencies compared with established solar cell technologies. However,their operational stability under different external stimuli is limited,and the underlying mechanisms are not fully understood. In particular,an understanding of degradation mechanisms from a morphology perspectiveduring device operation is missing. Herein, we investigate the operationalstability of PSCs with CsI bulk modification and a CsI-modified buriedinterface under AM 1.5G illumination and 75 & PLUSMN; 5% relative humidity,respectively, and concomitantly probe the morphology evolution withgrazing-incidencesmall-angle X-ray scattering. We find that volume expansion withinperovskite grains, induced by water incorporation, initiates the degradationof PSCs under light and humidity and leads to the degradation of deviceperformance, in particular, the fill factor and short-circuit current.However, PSCs with modified buried interface degrade faster, whichis ascribed to grain fragmentation and increased grain boundaries.In addition, we reveal a slight lattice expansion and PL redshiftsin both PSCs after exposure to light and humidity. Our detailed insightsfrom a buried microstructure perspective on the degradation mechanismsunder light and humidity are essential for extending the operationalstability of PSCs.

Automated summary

In this study, the operational stability of perovskite solar cells (PSCs) was investigated, and it was found that the absorption of water caused volume expansion within the perovskite grains, leading to the degradation of the cells and a decrease in their performance. It was also observed that modifying the buried interface of the PSCs can slow down the degradation.