Dopability in earth abundant chalcogenide absorbers: insights from computation Christopher Savory University College London, UK As we have to provide for an increasing global energy demand while balancing against the worsening effects of climate change, diversification of photovoltaic technologies and materials is crucial to meeting this demand by accessing more sustainable materials in a wider variety of device architectures and applications. While champion ‘thin-film’ materials such as CdTe allow strong absorption from nanometre-thin films and flexible devices not possible with crystalline silicon, they can suffer from toxicity and low abundance of constituent elements, 1,2 opening the search for earth abundant materials that are also strong absorbers and demonstrate advantages such as defect tolerance. This study entails our computational investigations into two emerging chalcogenide solar absorbers and their relative merits and weaknesses arising from their defect behaviour. Antimony Selenide is a highly promising candidate chalcogenide photovoltaic absorber, possessing a very high absorption coefficient, near-ideal band gap and relatively abundant constituent elements: high efficiencies are being achieved in devices, 3 and the pseudo-1D nature of the material, held together by van der Waals interactions, has been highlighted as a potential reason for benign grain boundaries. 4 Our recent theoretical work, however, using ab initio hybrid Density Functional Theory (DFT) has found that despite possessing an 'ns 2 ' cation chemistry previously highlighted to enhance defect tolerance, Sb 2 Se 3 actually demonstrates multiple intrinsic defects with mid-gap transition levels that could act as strong non-radiative recombination centres unless passivated. 5 Here, we discuss our calculations on extrinsic defects, including the impact of unintentional n-type contamination, 6 as well as potential extrinsic p-type dopants, and the limits of dopability attainable for the material. Germanium Selenide, more commonly examined in its monolayer form, may also be viewed as another ‘simple’ binary chalcogenide that holds complexity beneath the surface - for example, the uncertainty surrounding the direct nature of its band gap. 7 We will thus also discuss the intrinsic defect chemistry in GeSe, making comparisons to the predictions for Sb 2 Se 3 , and thus try to establish an understanding of the applicability of defect tolerance and dopability in chalcogenides such as these two materials. References 1. Haegel, N. M.; Margolis, R.; Buonassisi, T.; Feldman, D.; Froitzheim, A. et al. Science 356 , 141 (2017) 2. Peter, L. M. Trans. A. Math. Phys. Eng. Sci. 369 , 1840 (2011) 3. Li, Z.; Liang, X.; Li, G.; Liu, H.; Zhang, H.; Guo, J.; Chen, J.; Shen, K.; San, X.; Yu, W.; Schropp, R. E. I.; Mai, Y. Commun. 10 , 125 (2019) 4. Zhou, Y.; Wang, L.; Chen, S.; Qin, S.; Liu, X.; Chen, J.; Xue, D.-J.; Luo, M.; Cao, Y.; Cheng, Y.; Sargent, E. H.; Tang, J. Photonics 9 , 409 (2015) 5. Savory, C. N.; Scanlon, D. O. Mater. Chem. A 7, 10739 (2019) 6. Hobson, T.D.C.; Phillips, L.J.; Hutter, O.S.; Shiel, H; Swallow, J.E.N.; Savory, C.N.; Nayak, P.K.; Mariotti, S.; Das, B; Bowen, L. et al., Chem. Mater. 32 , 2621 (2020) 7. Murgatroyd, P.A.E.; Smiles, M.J.; Savory, C.N.; Shalvey, T.P.; Swallow, J.E.N. et , Chem. Mater. 32 , 3245 (2020)
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