Various thin-film I2-II-IV-VI4 photovoltaic absorbers derived from kesterite Cu2ZnSn(S,Se)4 have been synthesized, characterized, and theoretically investigated in the past few years. The availability of this homogeneous materials dataset is an opportunity to examine trends in their defect properties and identify criteria to find new defect-tolerant materials in this vast chemical space. We find that substitutions on the Zn site lead to a smooth decrease in band tailing as the ionic radius of the substituting cation increases. Unfortunately, this substitution strategy does not ensure the suppression of deeper defects and non-radiative recombination. Trends across the full dataset suggest that Gaussian and Urbach band tails in kesterite-inspired semiconductors are two separate phenomena caused by two different antisite defect types. Deep Urbach tails are correlated with the calculated band gap narrowing caused by the (2III + IVII) defect cluster. Shallow Gaussian tails are correlated with the energy difference between the kesterite and stannite polymorphs, which points to the role of (III + III) defect clusters involving Group IB and Group IIB atoms swapping across different cation planes. This finding can explain why in-plane cation disorder and band tailing are uncorrelated in kesterites. Our results provide quantitative criteria for discovering new kesterite-inspired photovoltaic materials with low band tailing.
Bibliographical noteFunding Information:
This project has received funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement No. 840751, and from VILLUM Fonden (grant no. 9455). The Center for Nano-structured Graphene is sponsored by the Danish National Research Foundation (Project No. DNRF103). The PL imaging setup has been partly funded by the IDUN Center of Excellence funded by the Danish National Research Foundation (project no. DNRF122) and VILLUM Fonden (grant no. 9301). This research has also been funded by the EU Horizon2020 Frame-work (STARCELL, Grant No. 720907). We are grateful to the UK Materials and Molecular Modelling Hub for computational resources, which is partially funded by EPSRC (EP/P020194/1). Via our membership of the UK’s HEC Materials Chemistry Consortium, which is funded by EPSRC (EP/L000202), this work used the ARCHER UK National Supercomputing Service (http:// www.archer.ac.uk).
© The Royal Society of Chemistry.