Efficiency enhancement of bifacial Cu2ZnSnSe4 thin-film solar cells on indium tin oxide glass substrates by suppressing In-Sn diffusion with Mo interlayer

Abstract

We fabricate bifacial Cu2ZnSnSe4 (CZTSe) thin-film solar cells on indium tin oxide (ITO) substrates using a vacuum procedure. We find that, as the annealing temperature increases from 500 to 540 °C, the performance of the CZTSe solar cell rapidly degrades due to Sn–In diffusion. We implement Mo interlayers at the CZTSe absorber/ITO interface to suppress this Sn–In movement. During annealing, the selenized Mo interlayer with MoSe2 effectively acts as a barrier layer to reduce the In diffusion into the CZTSe absorber. The relationship between the Mo thickness and the CZTSe performance is addressed. Because the Mo interlayer is used, the conversion efficiency of the CZTSe solar cells greatly improves, from 0.40% to 5.21% under front illumination. Also, the effects of the bifacial conditions and Mo interlayer thickness on the performance of the CZTSe solar cells are investigated. Under bifacial illumination (front: 1.0 sun/rear: 0.3 sun), the conversion efficiency of the CZTSe solar cells increases by up to 10% compared with that under front illumination only, achieving a value of 5.71% for CZTSe/ITO.