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Interface characteristics of CdS/Cu(In,Ga)Se2 thin-film solar cells by using photoreflectance spectroscopy

We investigated the CdS/Cu(In,Ga)Se2 interface characteristics of Cu(In,Ga)Se2 (CIGS) thin-film solar cells by using photoreflectance spectroscopy and their influence on the photovoltaic performance. We prepared CIGS solar cells with CdS and CIGS layers fabricated by using different methods of chemical bath deposition (CBD). The thiourea concentration in the CBD-CdS process was varied from 0.025 M to 0.1 M. The final In-Ga-Se deposition time for the CIGS film’s deposition was varied from 300 s to 490 s. We fabricated solar cells with thin films fabricated by using a combination of these conditions. The transition energies changed from 2.277 eV to 2.387 eV and the conversion efficiencies changed from 14.13% to 15.81% depending on the fabrication process. The formation of different states in CdS/CIGS resulted in different conversion efficiencies, as well as different band alignments at the CdS/CIGS interface.