Composition–Property Mapping in Bromide-Containing Tin Perovskite Using High-Purity Starting Materials

The wide band gaps of bromide-containing tin perovskites, ASnI3–xBrx, make them attractive materials for use as the top-layer absorber in tandem solar cells, as well as in single-junction solar cells for indoor applications. In the present work, a series of ASnI3–xBrx films was systematically fabricated by varying the A-site (FA+, MA+, and Cs+) and X-site (I– and Br–) ions. The use of a solvent-coordinated SnBr2 complex as a high-purity source of bromide combined with Sn(IV) scavenging treatment helps to ensure that the optimal film quality across the compositional space is realized. The energy levels and electronic properties of the films were characterized by photoemission yield spectroscopy and photoluminescence measurements. The films with long photoluminescence lifetime and favorable energy level alignment resulted in superior device efficiency when evaluated in standard single-junction solar cells. The best power conversion efficiency of 7.74% was obtained when the composition was FA0.75MA0.25SnI2.25Br0.75.