Elements substitution and doping in perovskite CH3NH3PbI3 exhibit versatile tunability of energy band structure and opto-electric properties. Ba2+ is chosen to substitute Pb2+ for its similar valence state and ionic radius with Pb2+. Ba2+ doping in perovskite (mol% <5) slightly enlarges the optic energy gap by conduction band minimum(CBM) upshifting to vacuum energy level, which is due to the smaller electronegativity of Ba than Pb. The enlarged band gap is also verified by density function theory calculations. In n-i-p structure perovskite solar cells (PSCs), because of the higher CBM of doped perovskite, the Fermi energy difference between n and p side is enlarged and the electron injection from the perovskite to TiO2 is improved. Thus, both the photovoltage and photocurrent are improved by small amount Ba2+ doping, resulting optimized 17.4% efficiency under AM1.5. This work reveals the relationship between the doping element property and the energy band structure of the perovskite, and highlights the doping method to improve the performance of PSCs. (C) 2017 Elsevier Ltd. All rights reserved.