Very-High-Concentration Challenges of III-V Multijunction Solar Cells

Abstract

This chapter focuses on the challenges that III-V multijunction cells (MJCs) must face when operating at very high concentrations inside optical concentrators. Only monolithically grown MJCs are considered because, in the opinion of the author, although mechanically stacked MJCs are able to achieve higher efficiencies (with the subsequent interest in their technological development) they are not cost competitive. The reason for this is the use of two or more semiconductor substrates as well as the strict optical alignment requirements between the stacked cells that lead to a very complicated manufacturing process. Although both issues could be overcome in the future, the present situation is that all the attempts to commercialize concentrator PV modules are based on monolithically grown MJCs [1–4].

Consequently, the first sect. of this chapter is devoted to the analysis of the operation of MJCs under real conditions. A description of the real operation factors limiting the MJC’s performance, such as non-uniform illumination impinging on the cell, paying special attention to the tunnel junction performance and its influence on the effects caused by series resistance, are presented. The second sect. is devoted to a specific approach able to circumvent the aforementioned effects: “the LED-like approach”. Finally, the third section presents a cost analysis of complete PV installations based on modules including MJCs manufactured following the “LED-like approach”.