Stability and performance improvement of cesium tin halide perovskites with astaxanthin treatment

Perovskite solar cells (PSCs) that are cesium (Cs)-based have better thermal and moisture stability than organic-based PSCs. However, cesium lead iodide (CsPbI3) is known for being highly toxic, while cesium tin iodide (CsSnI3) faces problems of poor crystallization and increased oxidation, which hinders their efficiency. Herein, an anti-oxidant known as astaxanthin (AXT) was used to improve the photovoltaic performance and stability of CsSnI3 PSC. X-ray diffraction (XRD) patterns and scanning electron microscopy (SEM) images indicated high crystallinity and good morphology in the AXT-treated films, respectively, indicating that the carbonyl group (CO) in AXT coordinated with Sn2+ for effective nucleation and crystal growth processes. According to X-ray photoelectron spectroscopy (XPS) results, the AXT-treated film contained higher Sn2+ concentration than the control film, indicating minimal oxidation for the former film. This was thought to have resulted from the high conjugation in AXT, which kept a rich electron density around Sn2+, thus minimizing the self-p-type doping in the perovskite. Hydrogen donation from the hydroxyl group (OH) in AXT neutralized the reactive oxygen species and facilitated the anti-oxidation process in the perovskite film. The champion unencapsulated AXT-treated device exhibited a 10.5% PCE, and 90% of it was retained after 1000 hours (h) of storage in inert conditions.