ABSTRACT
Heterojunctions based on CuGaSe2 are under investigation for photovoltaic applications since 1977, but their efficiency was limited mainly due to low open circuit voltages with respect to the band gap. In order to characterize this junction more detailed we present in this paper the analysis of the bandoffset between CuGaSe2 and CdS deposited by chemical bath deposition. X-ray photoelectron spectroscopy measurements reveal a valence band offset of ΔEV ≈ 0.9 eV between the absorber and the buffer layer. We also correlate those measurements to investigations of the dominant recombination mechanism in dependence of the substrate material and the Chemical bath CdS recipe. Ultraviolet Photoelectron Spectroscopy measurements exhibit an energetic difference of 0.8 eV between the Fermi-level and the valence band maximum indicating no conduction type inversion at the surface. Temperature and intensity dependent current-voltage measurements prove that junction related recombination processes are responsible for the voltage limitation.
