Atomic layer deposition of energy band tunable tin germanium oxide electron transport layer for the SnS-based solar cells with 400 mV open-circuit voltage

Abstract

Tin germanium oxide, (Sn,Ge)O2, films were prepared using atomic layer deposition and tailored to SnS absorber layer by incorporating various amounts of germanium into tin oxide to adjust band alignments at the interfaces of SnS/(Sn,Ge)O2 photovoltaic devices. Carrier concentrations of (Sn,Ge)O2 were suppressed from 1020 to 1018 cm-3 with germanium incorporation, with nitrogen doping of further reducing carrier concentrations by another order of magnitude. Excellent tunability of both band energy levels and carrier concentrations of (Sn,Ge)O2 allowed optimizing SnS-based solar cells. SnS/(Sn,Ge)O2:N devices were demonstrated, with an open-circuit voltage as high as 400 mV, due to effective mitigation of interfacial recombination of photogenerated carriers at the SnS/(Sn,Ge)O2:N absorber-buffer heterojunction interface.