Multivariate approach for studying the degradation of perovskite solar cells

Despite the progress in the performance of perovskite solar cells (PSCs), the absorber layer degradation during prolonged exposure to multiple environmental conditions is still a major issue. As the degradation depends upon many intrinsic and extrinsic factors, the need to adopt a multivariate testing protocol, which provides rapid assessment of device stability, is required. To do this, a Plackett Burman (PB) screening design has been used to analyze 9 different factors that affect the PSC stability; including four extrinsic factors (oxygen, moisture, UV exposure and temperature) and five intrinsic factors (selection of hole transport layer and electron transport layer, absorber layer thickness, halide type and perovskite deposition process). This approach allows us to rank the relative severity of these factors and can be used to narrow the scope of materials and device architectures to be modified, by identifying materials and configurations, which are the most stable. The least and most stable device configurations have been identified and the success of the screening approach has been demonstrated by testing the optimized configurations under ISOS-D1 and -L2 protocols. Importantly, only 12 experiments are needed to establish the most stable combination from the 9 factors thus providing a rapid assessment. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) measurements of perovskite absorber films have been performed in order to understand the degradation pathways and to support the conclusion of PB screening technique.