A comparative study of BSF layers for GaAs-based single-junction or multijunction concentrator solar cells

An effective back surface field is a key structural element for a high-efficiency GaAs concentrator solar cell, either in a multijunction or in a single-junction device. In this paper, several BSF materials are analysed, namely: (1) p(++)GaAs(Zn), (2) p(+)Ga(0.5)In(0.5)P(Zn) and (3) p(++)Al(0.2)Ga(0.8)As(C). The results of the comparison demonstrate that the best option is C-doped Al0.2Ga0.8As, which exhibits a low series resistance and behaves as an excellent minority carrier mirror; p(++)GaAs(Zn) shows reduced minority carrier mirror properties resulting from Zn diffusion and p(+)Ga(0.5)In(0.5)P(Zn) is shown to produce important series resistance problems because of an unfavourable heterojunction with GaAs.