High-throughput screening of polycrystalline solar absorbers (Ext.)

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This is an extension of the Fellowship: 'Non-equilibrium electron-ion dynamics in thin metal-oxide films' (EP/K003151/1).The development of low-cost high-efficiency solar cell devices would allow us to make more use of the vast amount of free and clean energy available in sunlight. Materials which absorb light to generate energetic electrons in solar cells are known as solar absorbers. In current consumer level solar cells the solar absorber is crystalline silicon. Silicon based cells exhibit high efficiencies (~25%) but are relatively expensive to produce. For example, it currently takes about 14 years of operation for a typical 4 kW domestic installation to break even (e.g. see http://www.theecoexperts.co.uk/are-solar-pv-panels-good-investment). Driven by the desire to reduce cost there has been a continued focus on the development of new high-efficiency solar absorber materials that are less expensive to manufacture than silicon to form the basis of next generation solar cell technologies.A general trend in materials development has been the progression from silicon towards more complex binary, ternary and quaternary compound semiconductors, which offer a wider compositional and structural parameter space within which desired properties can be optimised. Highly performing examples include CuInGaSe2, CdTe, Cu2ZnSn(S,Se)4 (CZTS) and lead-halide perovskites (e.g. CH3NH3PbI3, MAPI). Unlike silicon these emerging materials often contain relevantly high concentrations of point defects since they are almost always non-stoichiometric. They are also usually polycrystalline and grain boundaries (together with associated point defects) are known to affect material performance by contributing to non-radiative electron-hole recombination and reduction of open circuit voltage (both effects that reduce efficiency). While predictive computational materials screening approaches have proved invaluable in helping to identify promising solar absorber materials there are currently no screening approaches that consider the properties of grain boundary defects. This proposal aims to fill this critical gap in the materials modelling toolbox by developing systematic approaches to screen materials against the thermodynamic and electronic properties of grain boundaries. These approaches will be applied to identify optimal compositions and dopants for CdTe, lead-halide perovskites and CZTS materials to help optimise performance and accelerate innovation. We will work closely with experimental collaborators and our industrial partner (Dyesol) to validate theoretical models and test predictions in order to deliver improvement in solar cell performance. The computational screening approaches we develop will also be made available to the wider materials modelling community and will find application in many other areas where the electronic properties of grain boundaries impact on material performance (including thermoelectrics, batteries, photoelectrochemical cells, varistors, transparent conducting oxides and dielectrics to name a few).