Nanoscale Electrical Properties of Wide-Bandgap Cu(In,Ga)Se2 and Cu2ZnSn(SSe)4 Thin Films

We report microscopic characterization studies of wide-bandgap Cu(In,Ga)Se-2 (CIGSe) and wide-bandgap Cu2ZnSn(SSe)(4) (CZTSS) thin films using the nanoscale electrical probes of scanning Kelvin force microscopy and scanning spreading resistance microscopy. These films were deposited by the co-evaporation of the elements in a vacuum. The CIGSe films are NREL's recently improved wide-bandgap devices. The potential imaging shows significant increase in surface potential roughness with increasing the bandgaps, indicating degradation of the film surface by charge-trapping defects. These defects are expected to significantly affect open-circuit voltage after the surfaces are turned to junction upon device completion. The resistance imaging shows increase in both the overall resistance and resistance nonuniformity, likely because of defect scattering to carrier transport.