In Situ Identification of Photo- and Moisture-Dependent Phase Evolution of Perovskite Solar Cells

Photovoltaic performance of a perovskite solar cell is observed to decrease with increasing humidity, which might be attributed to the formation of hydrated intermediates leading to a decrease in extraction of photocarriers. However, direct evidence of the interplay between the perovskite layer and the photovoltaic performance under operating conditions (consecutive illumination) has not yet been reported. Herein, we investigated the degradation of perovskite solar cells under operating situations through in situ X-ray diffraction and in situ X-ray absorption spectroscopies, which revealed that lead hydroxide iodide (PbIOH), a new phase that has not previously been identified as the degradation product of perovskite solar cells, was formed as an end decomposition product inside the cell. The formation of PbIOH could break the interface inside and be the key reason behind the problem of reduced cell life. This work illustrates that in operando direct observation of the photo- and moisture-induced effects can provide needed insights toward realizing stable perovskite solar cells.