Bandgap Variations for Large Area Cu(In,Ga)Se2 Module Production

Abstract

The development of large area Cu(In,Ga)Se 2 photovoltaic (PV) modules has reached a remarkable level. Nevertheless, scope for further improvement lies in the ability of the Cu(In,Ga)(Se,S) 2 alloy system to vary the bandgap via the In-to-Ga or the S-to-Se ratio. This chapter investigates the possible gain in efficiency resulting from a better match to the solar spectrum, reduced losses related to the monolithic integration and an improved temperature coefficient, all of which are achievable by increasing the bandgap energy of the absorber material. Experimental results are compared to theoretical predictions and the deviations are discussed. Furthermore, graded bandgap structures, obtainable by introducing compositional profiles in the depth of the absorber, have demonstrated their potential to improve the conversion efficiency. Nevertheless, so far the potential of graded bandgap structures has not been fully exploited for large area module production. In this chapter, the technical feasibility of depositing absorbers with a graded bandgap on a large area is shown and the effect on the electrical characteristic is discussed.