Semiconductor physics of halide perovskite solar cells*

Perovskites are the wonder compounds of materials science, with recent applications in high-efficiency solar cells. This talk will address the physical properties that make halide perovskites unique. After five years of intensive research, there has been a number of breakthroughs in understanding, but many challenges remain.

Our research has addressed the origin of the success of methylammonium lead iodide photovoltaics from multi-scale materials modelling [1-4]. These organic-inorganic materials satisfy the optoelectronic criteria for an active photovoltaic layer, i.e. spectral response in the visible range combined with light electron and hole effective masses. In addition, these systems are structurally and compositionally flexible with large dielectric constants, and the ability to alloy on each of the lattice sites.

I will discuss issues ranging from disorder associated with molecular vibrations and rotations within the inorganic network, to microscopic polarisation arising from correlations in cell dipole orientations. The temporal behaviour of hybrid perovskites has recently been validated through a combination of neutron scattering, time-resolved vibrational spectroscopy, and kinetic measurements of the current-voltage response. The implications for electron-hole recombination and new models for the cooling of hot carriers in operating solar cells will be discussed.

1. “Atomistic origins of high-performance in halide perovskite solar cells” Nano Letters, 14, 2584 (2014)
2. “Self-regulation mechanism for charged point defects in halide perovskites” Angewandte Chemie Int. Ed. 54, 1791 (2015)
3. "Direct observation of dynamic symmetry breaking above room temperature in methylammonium lead iodide" ACS Energy Lett. 1, 880 (2016)
4. "Slow cooling of hot polarons in halide perovskite solar cells" ACS Energy Letters 2, 2647 (2017)