Proposal for realizing high-efficiency III-nitride semiconductor tandem solar cells with InN/GaN superstructure magic alloys fabricated at raised temperature (SMART)

We propose a plausible and realistic idea for realizing high-efficiency III-nitride semiconductor tandem solar cells which utilize nearly entire AM-1.5 solar spectrum conversion under a subcell photocurrent matching rule. For the sake of drastic improvement/suppression of pn-junction leakage current, each subcell in the proposed tandem solar cells is composed of superstructure InN/GaN magic alloys, i.e. coherently grown (InN)m/(GaN)n short-period superlattices with simple integer pairs of (m, n) ≤ 4 in monolayers, which solve lattice-mismatch and immiscible problems in a conventional InGaN ternary alloy system. The InN/GaN magic alloys are further applicable to band engineering that provides potential wells for a thermal/photo sensitization effect and graded-bandgap structures for efficient carrier collection under the same (m, n) ratio alloys or keeping the coherent structure. Theoretical maximum conversion efficiency is 51% (58% under 250-suns concentration) for a 4-tandem cell configuration.