Effect of Ge Incorporation on Lead‐free Cs‐based Triiodide Sn−Ge Co‐alloy Perovskite Thin Films by Spin Coating

Abstract A new Sn−Ge co‐alloy perovskite that does not contain toxic Pb is attracting attention due to its excellent predicted optoelectronic properties. However, most current research only focuses on compositions with Ge content up to 50 %, resulting in a limited overall understanding on this material system. In this study, CsSn 1– x Ge x I 3 (0≤ x ≤1) perovskite thin films were fabricated using spin coating method and characterized in terms of crystallographic, morphological and optical characteristics systematically. The results show that the Ge incorporation causes lattice shrinkage and a change in the crystallographic phase from orthorhombic to trigonal. Additionally, the coverage varies much as Ge increases. The Ge incorporation also results in a blueshift of the photoluminescence peak and a decrease in luminescence intensity as compared to the composition with lower Ge content. Moreover, the carrier dynamics measurement shows that the Ge incorporation increases the carrier nonradiative recombination. This work provides important hints for the development of the Sn−Ge alloy‐based perovskite solar cell.