Multijunction concentrator solar cells

Abstract

Tandem solar cells based on III-V materials have achieved the highest efficiencies of any present photovoltaic device. Conversion efficiencies up to 39% ∼240 sun concentration [1] have been reported, and efficiencies > 40% are foreseen in the near future. Additionally, these devices are presently the only available solar cells reaching efficiencies above 30%. The high efficiency is due to the reduction of thermalization and transmission losses in solar cells when the number of p-n junctions is increased (see Fig. 4.1); however, the higher costs of these solar cell materials compared with silicon or thin-film devices prohibit their application in flat-plate modules on earth. The solution to this cost-efficiency dilemma is their use in high-concentration systems, thereby replacing the expensive solar cell materials by cheaper optics. In this chapter, we describe the background to the research development on multijunction solar cells. In the first part we discuss the early developments and approaches for realizing high-efficiency multijunction solar cells. Then we present state-of-the-art technologies for manufacturing multijunction solar cells. In the next sect. we concentrate on the characterization of monolithic multijunction solar cells, still a challenging issue which is often not properly addressed. (This is especially true for concentrator solar cells.) Finally, an overview of new approaches for reaching even higher conversion efficiencies > 40% in the future is given. 2007 Springer-Verlag Berlin Heidelberg.