Optical Characterization of Lead-Free Cs₂SnI₆ Double Perovskite Fabricated from Degraded and Reconstructed CsSnI₃ Films

Halide perovskites have experienced a huge development in the past years, but they still have two major challenges for their massive implantation: the long-term stability and the use of lead. One of the most obvious lead-free candidates to replace these perovskites is CsSnI3, but due to its poor environmental stability, it has been discarded for the fabrication of stable devices. Nevertheless, ambient degradation of CsSnI3 and ulterior reconstruction produce a relatively stable lead-free Cs2SnI6 double perovskite with interesting optical properties that have not been deeply characterized previously. In this work, the potential use for the optical properties of Cs2SnI6 is studied and compared with that of the most common halide perovskite, CH3NH3PbI3 (MAPbI3). The Cs2SnI6 films stayed in a standard atmosphere for a week without showing any signs of degradation. They also demonstrated better reflective behavior than MAPbI3 and higher absorption in the 650 and 730 nm spectral range, making this material interesting for the development of photodetectors in this region. This study demonstrates that Cs2SnI6 is a promising material for photodevices, as it highlights its main characteristics and optical parameters, giving an original view on the use of the double perovskite, but at the same time emphasizing the need to improve the electrical properties for the development of efficient optoelectronic devices.