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

Highlights: • We reported, for the first time, B-site minor doping engineering of CsPbI₃ perovskites. • The perovskite bandgaps have been finely aligned by B-site minor doping of Sn²⁺, Ge²⁺ and Si²⁺. • Minor doping of 2.8 at.% Sn²⁺ could enhance the stability and optical performance synergistically. • The deeply physics of B-site minor doping engineering of perovskites has been proposed. -- Abstract: A relatively wide bandgap and intrinsically phase instability of α-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 CsPb_1-xB_xI₃ 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.