Hartmann, C.; Brandt, R.E.; Baranowski, L.L.; Köhler, L.; Handick, E.; Félix, R.; Wilks, R.G.; Zakutayev, A.; Buonassisi, T.; Bär, M.: Chemical and electronic structure of the heavily intermixed (Cd,Zn)S:Ga/CuSbS2 interface. Faraday Discussions 239 (2022), p. 130-145
10.1039/d2fd00056c
Open Access Version
Abstract:
The interface formation and chemical and electronic structure of the (Cd,Zn)S:Ga/CuSbS2 thin-film solar cell heterojunction were studied using hard X-ray photoelectron spectroscopy (HAXPES) of the bare absorber and a buffer/absorber sample set for which the buffer thickness was varied between 1 and 50 nm. We find a heavily intermixed interface, involving Cu, Zn, and Cd as well as significant Ga and Cu profiles in the buffer. The valence band (VB) offset at the buffer/absorber interface was derived as (−1.3 ± 0.1) eV, which must be considered an upper bound as the Cu diffused into the buffer might form a Cu-derived VB maximum located closer to the Fermi level. The estimated conduction band minimum was ‘cliff’-like; a situation made more severe considering the Cu-deficiency found for the CuSbS2 surface. The complex interface structure’s effect on the performance of (Cd,Zn)S:Ga/CuSbS2-based solar cells and its limitation is discussed together with possible mitigation strategies.