Bandgap alignment of α-CsPbI3 perovskites with synergistically enhanced stability and optical performance via B-site minor doping

A relatively wide bandgap and intrinsically phase instability of alpha-CsPbI3 perovskites (PVSKs) greatly hinder their potential applications in solar cells. One of the popular solutions is based on high-concentration doping, which however encounters big difficulty in the balance between phase stability and optical performance. Here, we report the advance on bandgap alignment of CsPbI3 through B-site (Pb2+ cation) minor doping engineering employing density functional theory (DFT). It is discovered that the bandgaps could be finely aligned by minor doping of Si2+, Sn2+ and Ge2+, which is caused by the downshift of conduction band minimum contributed by B-p orbital level within CsPb1-xBxI3 PVSKs, and thus offer shrunken gaps and enlarged imaginary part of dielectric function for enhanced photo absorption. Furthermore, the minor doping of Sn2+ could not only bring a suitable tolerance factor for CsPbI3 with a slighter lattice distortion, but also increase the charge density of Pb2+ to enhance the interaction between Pb2+ and I-, which consequently improve their structure stability.