Tuning the Photoelectric Properties of Perovskite Materials Using Mg/Ge/Si and Br Double-Doped to FASnI3

Formamidinyl tin iodide (FASnI3, FA+ = NH2CHNH2 +) has attracted enormous attention due to the higher thermal stability, less pollution, and excellent photoelectric properties. However, oxidation of tin may result in tin vacancy defects, which not only reduce the photoelectric conversion efficiency (PCE) but also limit its practical application in perovskite solar cell materials. In this paper, to restrain the oxidability and improve the PCE of the structure, Mg/Ge/Si and Br double-doped to FASnI3 were studied by density functional theory (DFT). The results about geometric and photoelectric properties show that appropriate doping can increase the stability, tune the band gap, and improve the charge transfer balance. Among all the discussed doping ratios, FASn0.75Mg0.25I2Br and FASn0.75Mg0.25IBr2 are expected to be used as candidates for the light-absorbing layer of perovskite solar cells because of their high stability and excellent properties.