Relativistic quasiparticle self-consistent electronic structure of hybrid halide perovskite photovoltaic absorbers

Solar cells based on a light absorbing layer of the organometal halide\nperovskite CH$_3$NH$_3$PbI$_3$ have recently reached 15% conversion efficiency,\nthough how these materials work remains largely unknown. We analyse the\nelectronic structure and optical properties within the quasiparticle\nself-consistent GW approximation. While this compound bears some similarity to\nconventional sp semiconductors, it also displays unique features. Quasiparticle\nself-consistency is essential for an accurate description of the band\nstructure: bandgaps are much larger than what is predicted by the local density\napproximation (LDA) or GW based on the LDA. Valence band dispersions are\nmodified in a very unusual manner. In addition, spin orbit coupling strongly\nmodifies the band structure and gives rise to unconventional dispersion\nrelations and a Dresselhaus splitting at the band edges. The average hole mass\nis small, which accounts for the long diffusion lengths recently observed. The\nsurface ionisation potential (workfunction) is calculated to be 5.7 eV with\nrespect to the vacuum level, explaining efficient carrier transfer to TiO$_2$\nand Au electrical contacts.\n