Bandgap engineering for optimal antimony chalcogenide solar cells

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Antimony sulphur-selenide Sb2(S,Se)3 is an emerging material for solar photovoltaics of significant promise. Currently the performance limit is ~10% PCE but theoretical predictions suggest it has the potential to outperform current thin-film market leader CdTe. Sb2(S,Se)3 has two properties we can harness to improve performance: i) the bandgap easily can be tuned from 1.18-1.70eV by variation of the S/Se ratio, ii) it is can readily be doped both n and p-type via extrinsic dopants. These properties allow us to tailor and manipulate the absorber bandgap and/or doping level throughout the absorber material for improved carrier extraction. Importantly this bandgap manipulation can be achieved using a specially designed deposition capability which is a single step, industrially scalable deposition process. The project will develop this approach and link from materials synthesis with controlled doping, to device performance analysis and in-depth materials/interface characterisation. By tracking performance improvements in parallel to materials analysis we can identify and eliminate limitations at every step of the production process. This approach will not only allow us to make better use of the solar spectrum but also overcome the low voltages (< 40% of theoretical limit) which currently restrict Sb2(S,Se)3 device performance. We will achieve this by using designed bandgap grading with profiles to improve carrier lifetimes, reduce interfacial recombination and thereby improve generated voltage. We will also advance the state of the art by using intentional doping of the material via extrinsic dopants whilst in parralel tracking the impact on deep level behaviour and recombination - a radical departure from the current worldwide practice of relying on conductivity from native defects.This project will accelerate the development process to capitalise on a material of huge potential. Our graded bandgap and controllably doped Sb2(S,Se)3 solar cells will open up new market opportunities in low-cost large scale power generation, but the ability to control the bandgap will also deliver opportunities for an expanded product range, such as wider gap devices for applications such as indoor PV (the 'internet of things'), top cells for Si-tandems or flexible devices.