Unraveling Interface Characteristics of Zn(O,S)/Cu(In,Ga)Se2 at Nanoscale: Enhanced Hole Transport by Tuning Band Offsets

•We fabricated Zn(O,S) buffered CIGS solar cells with controlled oxygen and sulfur ratio.•Carrier transport is enhanced by tuning the interfacial band offsets between the absorber and the buffer.•Depth-profiling of spatial work function of the devices was examined by Kelvin probe force microscopy.•A spike-like band offsets at the CIGS cell with Zn(O,S) grown by 1.3% O2 gas ratio show an optimal efficiency.