Bridging the Gap: Modeling the variation due to grain size distribution in CdTe solar cells

In this paper, we develop a multi-scale, hierarchical cell-to-module modeling approach to interpret and predict the effects of average grain size and grain size distribution on the cell efficiency of polycrystalline thin film solar cells, specifically, that of close space sublimated (CSS) CdTe. Our results explain why (1) increasing grain size improves cell performance, (2) the performance saturates beyond a critical grain size, (3) the effect of grain size distribution is averaged over larger length-scales, and therefore, (4) the observed empirical distribution of module efficacy must be attributed to sources other than grain-size distribution.