Abstract
Metal halide perovskites are rivaling established materials for thin film photovoltaics. Being able to tune interfacial alignment of energy levels may allow a further boost to the efficiency of perovskite optoelectronic devices. By using Density Functional Theory (DFT) modeling and experimental analysis, we show that the band edge energies of the prototypical MAPbI(3) (MA = methylammonium) perovskite can in principle be varied by as much as 1 eV via postsynthetic chemical treatment. In particular, MAI-rich (PbI2-rich) surfaces induce an energy upshift (downshift) of the perovskite band energies, and this can either inhibit or favor hole transfer at the perovskite/HTL interface.