Development Strategy of Thin Film Solar Cells: Low-cost & High-efficiency

Thin film solar cells have attracted much attention due to their potentials in efficiency as well as cost. Among the thin film solar cells, Cu(Ga,In)Se-2 (CIGS) compound semiconductors have been extensively studied as a promising absorber material for utilizing solar energy. In fact, the CIGS solar cells have shown a maximum cell efficiency exceeding 22.9% in the laboratory scale. Various technologies, that include co-evaporation, 2-step sputtering, and chemical vapor deposition, have been developed to fabricate high efficiency CIGS solar cell. In present, commercialization of CIGS has achieved using 2-step sputtering process, by Japanese company Solar Frontier Co.. Nevertheless, cost and efficiency issues are still important in CIGS solar cell manufacturing. Several years ago, our group have suggested one-step sputtering process, in which we do not carry out an additional selenization process, as a promising fabrication technologies of CIGS thin films. The process has the potential to manufacture high efficiency CIGS solar cell at relatively low cost. In this presentation, we report that our results on the CISG solar cells fabricated using one-step sputtering process and discuss the development strategy of thin film solar cells in view point of cost and efficiency.