Bismuth Doping–Induced Stable Seebeck Effect Based on MAPbI₃ Polycrystalline Thin Films

Abstract In this article, the thermoelectric properties of a Bi‐doped CH₃NH₃PbI₃ (MAPbI₃) perovskite thin film are studied. Bi‐doped MAPbI₃ thin film samples are fabricated, and it is found that Bi doping could greatly enhance the stability and thermoelectric properties of MAPbI₃. The Bi dopant located at the grain boundaries to modify the carrier channel near grain boundaries, which is observed via scanning electron microscopy and atomic force microscopy, efficiently reduces ion migration and facilitates charge transport. In addition, the Bi dopant can also passivate the defects in bulk MAPbI₃, increasing the polarization effect of MAPbI₃ which is demonstrated by the capacitance‐frequency measurement, thus greatly enhancing the mobility of Bi‐doped MAPbI₃. In addition, Bi‐doped MAPbI₃ leads to grain size reduction; the small size effect not only effectively hinders the MAPbI₃'s crystal phase transition from the tetragonal phase to the cubic phase, but it could also make the structure of MAPbI₃ more stable. Especially, the Seebeck voltage variation of Bi‐doped perovskite was less than that of the undoped one, meaning Bi doping would lead to a much more stable state in MAPbI₃ thin films. The results show that Bi‐doped MAPbI₃ is a promising approach to develop high stable thermoelectric and photovoltaic properties in organic–inorganic hybrid perovskite materials.