Origin of Interface Limitation in Zn(O,S)/CuInS2-Based Solar Cells

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 currentvoltage 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) spikelike 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 nearinterface defects (as recently observed in Cu-rich CuInSe2) as the likely reason for the performance-limiting interface recombination.

Automated summary

In devices based on Zn(O,S)/CuInS2, interface recombination is mainly caused by defects near the interface rather than unfavorable energy-level alignment or Fermi-level pinning. Research has shown that the dominant recombination channel is present at the Zn(O,S)/CuInS2 interface.