Perovskites are the wonder compounds of materials science, with examples of ferromagnets, ferroelectrics, multiferroics, superconductors, semiconductors, ion conductors, insulators and, most recently, highly efficient photovoltaics. This talk will address the chemical and physical factors that make these materials, and in particular hybrid organic-inorganic halide perovskites, unique.
Recently, we have been addressing the success of methylammonium lead iodide in solar cells from atomistic and electronic structure modelling [1-3]. The hybrid material satisfies the basic optoelectronic criteria essential for an active photovoltaic layer (spectral response with light electron and hole effective masses). Relativistic and many-body corrections are shown to be essential to describing the electronic band structure. In addition, the system is structurally and compositionally flexible with large dielectric constants, and the ability to alloy on each of the three perovskite lattice sites.
One anomalous behaviour of hybrid perovskite solar cells is hysteresis in the photovoltaic current-voltage response, which we demonstrate has a contribution from the orientational disorder of the methylammonium cations. The rotation-libration of the molecular dipoles results in a rich domain structure that is sensitive to both temperature and the external electric field.
1. F. Brivio, A. B. Walker and A. Walsh, APL Materials 1, 042111 (2013)
2. J. M. Frost, K. T. Butler, F. Brivio, C. H. Hendon, M. van Schilfgaarde and A. Walsh, Nano Letters, 14, 2584 (2014)
3. F. Brivio, K. T. Butler, A. Walsh and M. van Schilfgaarde, Physical Review B 89, 115204 (2014)