Valence and conduction bands engineering in halide perovskites for solar\n cell applica- tions

We performed ab initio simulations aimed at identifying the atomistic and\nelectronic structure origin of the high valence and conduction band, and band\ngap tunability of halide perovskites. We found that the two key ingredients are\nthe overlap between bivalent cation and halide atomic orbitals, and the\nelectronic charge of the bottom of the conduction band (CBM) state on the Sn or\nPb atoms. In particular, we found that lower gaps are associated to higher\nnegative antibonding overlap, and higher CBM charge on the bivalent cation.\nBoth overlap and CBM charge on Sn/Pb can be tuned by the chemical nature of\nhalide, bi and monovalent cation, as well as the symmetry of crystal structure.\nOn the basis of our results we provide some practical rules to tune the valence\nband maximum, conduction band minimum, and band gap in this class of materials.\n