n-Type Doping and Energy States Tuning in CH3NH3Pb1–xSb2x/3I3 Perovskite Solar Cells

Built-in field and energy band alignment decide the charge separation and transportation in perovskite solar cells. Composition change in perovskites to tune the energy states is thus valuable to try. In contrast to the equivalent substitution of Pb, here trivalent Sb is for the first time incorporated into CH3NH3PbI3, with a tuned optical band gap from 1.55 to 2.06 eV. Density function theory (DFT) calculations unveil the enlarged energy band gap and n-type doping property by Sb with more valence electrons than Pb. n-Type doping by Sb elevates the quasi-Fermi energy level of the perovskite/TiO2 and promotes electron transport in the working solar cell. Thus, the doped perovskite solar cell gains a lot in photovoltage while maintaining a high photocurrent, resulting in enhanced performance of 15.6% (0.956 sun, AM1.5). The results highlight the method of n/p-type doping of perovskites by heterovalent elements and its tunability to the energy states.