Influence of the optical and recombination losses on the efficiency of CdS/CdTe solar cell at ultrathin absorber layer

Abstract

The effect of low thickness of CdTe on optical, front, and back recombination losses and hence on the efficiency of a CdS/CdTe solar cell is studied theoretically in this work. It is found that the optical losses are about 23%–24% and depend weakly on CdTe thickness. The recombination losses are about 28% at dCdTe = 0.45 μm and decrease to 23% at dCdTe = 1.1 μm because the recombination losses have significant effects at thinner layers. The recorded efficiency is in the 9.5%–10.5% range corresponding to the thickness of CdTe of 0.45–1.1 μm and it is considered in good agreement with experimental results. The electron diffusion length is in the range of 1.6–15.8 μm and corresponds to 10−9–10−7 s of the electron lifetime is sufficient to make the current density reaches its maximum value (16.3 mA/cm2) at dCdTe = 1.1 μm with efficiency of 10.5%.When the CdTe thickness is assumed to be 5 μm, which is often used in the fabrication of CdTe-based solar cells, the calculated current density is about 20 mA/cm2 and the corresponding efficiency is 13%. The present results lead to the shrinking of the gap between the theoretical and practical results and contribute to improving the efficiency of CdS/CdTe cells in the future.