Quality control and characterization of Cu(In,Ga)Se sub(2)-based thin-film solar cells by surface photovoltage spectroscopy

Surface photovoltage spectroscopy (SPS) has been used for quality control of ZnO/CdS/ Cu(In,Ga)Se sub(2) (CIGS) thin-film solar cells. The results show that SPS makes it possible to detect `hard failures' following CIGS deposition, and both `hard' and `soft' failures following CdS deposition and following ZnO deposition. In addition, a semi-quantitative screening of CdS/CIGS and ZnO/CdS /CIGS samples is possible. Hence, SPS is suggested as a useful tool for in-line monitoring of CIGS-based solar cell production lines. Moreover, SPS is shown to yield important new information regarding CIGS-based solar cells: (a) A deep gap state is found in samples of superior performance. (b) As opposed to the CdS/CIGS structure, a marked decrease in the open-circuit voltage upon Na contamination in ZnO/CIGS structures is found.