Surface electronic characterisation of Cu 2 ZnSn(S,Se) 4 films prepared from Sn(II) and Sn(IV) precursor sources Alice Sheppard 1 , Raphael E. Agbenyeke 1 , Isabella Nicholson 1 , Jude Laverok 2 , Devendra Tiwari 3 , Nicole Fleck 3 , Neil A. Fox 1,2 , David J. Fermin 1 1 School of Chemistry, University of Bristol, UK, 2 Physics Laboratory, University of Bristol, UK 3 Northumbria University, UK Cu 2 ZnSn(S,Se) 4 (CZTSSe) thin film photovoltaic devices are currently limited by significant voltage (Voc) losses, linked to the formation of Sn secondary phases and deep-level Sn Zn point defects and clusters, causing bandgap fluctuations and tailing, and reducing the minority carrier lifetime. A recent study has shown that replacing Sn(II) precursors by Sn(IV) complexes in solution based processed CZTSSe can lead to a substantial increase in device performance [1]. Building on our previous work [2,3], in this study, energy-filtered photoemission electron microscopy (EF-PEEM) has been used to visualise the surface electronic landscape of the CZTSSe absorber,on the sub-micron scale,upon fabricating films using Sn(II) and Sn(IV) precursor sources. Employing a Sn(IV) precursor, rather than Sn(II), reduces the presence of Sn(II) associated low work function (WF) hotspots, leading to a more uniform WF distribution. An average overall increase in WF of CZTSSe films, from 5.05 +/-0.05 eVto 5.15 +/-0.02 eV, was measured when using Sn(II) and Sn(IV) precursors respectively. References 1. Y. Gong, Y. Zhang, E. Jedlicka, R. Giridharagopal, J. A. Clark, W. Yan, C. Niu, R. Qiu, J. Jiang, S. Yu, S. Wu, H. W. Hillhouse, D. S. Ginger, W. Huang, H. Xin, Sci China Mater., 2021, 64, 52-60 2. D. Tiwari, M. Cattelan, R. L. Harniman, A. Sarua, A. Abbas, J. W. Bowers, N. A. Fox, D. J. Fermin, iScience, 2018, 9, 36-46 3. D. Tiwari, M. Cattelan, R. L. Harniman, A. Sarua, N. A. Fox, T. Koehler, R. Klenk, D. J. Fermin, ACS Energy Lett., 2018, 3, 2977-2982
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