Sood, M.; Bombsch, J.; Lomuscio, A.; Shukla, S.; Hartmann, C.; Frisch, J.; Bremsteller, W.; Ueda, S.; Wilks, R.G.; Bär, M.; Siebentritt, S.: Origin of Interface Limitation in Zn(O,S)/CuInS2-Based Solar Cells. ACS Applied Materials & Interfaces 14 (2022), p. 9676-9684
10.1021/acsami.1c19156
Open Access Version
Abstract:
Copper indium disulfide (CuInS2) grown under Cu-rich conditions exhibits high optical quality but suffers predominantly from charge carrier interface recombination, resulting in poor solar cell performance. An unfavorable “cliff”-like conduction band alignment at the buffer/CuInS2 interface could be a possible cause of enhanced interface recombination in the device. In this work, we exploit direct and inverse photoelectron spectroscopy together with electrical characterization to investigate the cause of interface recombination in chemical bath-deposited Zn(O,S)/co-evaporated CuInS2-based devices. Temperature-dependent current–voltage analyses indeed reveal an activation energy of the dominant charge carrier recombination path, considerably smaller than the absorber bulk band gap, confirming the dominant recombination channel to be present at the Zn(O,S)/CuInS2 interface. However, photoelectron spectroscopy measurements indicate a small (0.1 eV) “spike”-like conduction band offset at the Zn(O,S)/CuInS2 interface, excluding an unfavorable energy-level alignment to be the prominent cause for strong interface recombination. The observed band bending upon interface formation also suggests Fermi-level pinning not to be the main reason, leaving near-interface defects (as recently observed in Cu-rich CuInSe2) as the likely reason for the performance-limiting interface recombination.