Ab-Initio Computations of Electronic Structures of Methylammonium Lead Bromide/Iodide Perovskites as Wide Bandgap Active Materials in Solar Cells

Studies on the electronic structure of organo-lead halide perovskites have been much investigated in the last few years, as solar cells based on this novel materials exhibit high power conversion efficiency. In order to improve the chemical stability and vary the bandgap, for developing a solar cell with bulk heterojunction, the modification of this perovskite with hetero halide ions structure has also been investigated. We report here the electronic structure of Methylammonium lead bromide/iodide or MAPb(Br_xI_3-x)₃ at different contents of bromide ions investigated by an ab-initio computation based on Density Functional Theory (DFT) using Quantum Espresso. The calculated results show the increment of bands gap with increasing bromide ion concentration. The obtained Densities of States show that the addition of bromide ions plays an important role in constructing their valence band, where it is predominated by the electrons at the outermost orbital of these halide (Br^- and I^-) ions. On the other hand, the conduction band is still predominated by the 6p orbitals of the Pb²⁺ ions, in agreement with some reports elsewhere. The organic molecule orbitals, however, seems to give insignificant influence to those valence and conduction bands. (paper)