Investigation of p-type emitter layer materials for heterojunction barium disilicide thin film solar cells

Abstract

To achieve heterojunction thin film solar cells with high conversion efficiency using BaSi2 as a photoabsorption layer, we investigated the effects of electron affinity (χ) and the band gap (Eg) of a p-type semiconductor on the performance of BaSi2 thin film solar cells with a one-dimensional device simulator, Afors-HET ver. 2.5. By simulation, we found that χ should be less than 3.5 eV and Eg should be in the range of 1.5–2.5 eV to achieve a conversion efficiency of more than 20% in the case of p-type semiconductor/n-type BaSi2 active layer/n++-type BaSi2/electrode. Ultimately, we selected Zn3P2 (Eg = 1.5 eV, χ = 3.2 eV) and SnS (Eg = 1.3 eV, χ = 3.6 eV) as options for p-type materials. In particular, Zn3P2 maintains high efficiency even if a very thin oxide layer exists at the pn heterointerface. The highest conversion efficiency of p-type Zn3P2/n-type BaSi2 thin film solar cells was 23.17% without any light-trapping structure.