Solar cells based on a light absorbing layer of the organometal halide perovskite CH3NH3PbI3 have recently surpassed 15% conversion efficiency, though how these materials work remains largely unknown. We analyze the electronic structure and optical properties within the quasiparticle self-consistent GW approximation. While this compound bears some similarity to conventional sp semiconductors, it also displays unique features. Quasiparticle self-consistency is essential for an accurate description of the band structure: Band gaps are much larger than what is predicted by the local-density approximation (LDA) or GW based on the LDA. Valence band dispersions are modified in a very unusual manner. In addition, spin-orbit coupling strongly modifies the band structure and gives rise to unconventional dispersion relations and a Dresselhaus splitting at the band edges. The average hole mass is small, which partially accounts for the long diffusion lengths observed. The surface ionization potential (work function) is calculated to be 5.7 eV with respect to the vacuum level, explaining efficient carrier transfer to TiO2 and Au electrical contacts.
|Physical Review B - Condensed Matter and Materials Physics
|Published - 21 Apr 2014