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

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 d_CdTe = 0.45 μm and decrease to 23% at d_CdTe = 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 d_CdTe = 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. (author)