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

Abstract

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.