Dependence of the efficiency of a CdS/CdTe solar cell on the absorbing layer’s thickness

On the basis of the continuity equation, the spatial distribution of photogenerated excess electrons in the neutral region of the CdTe layer in a CdS/CdTe heterostructure is analyzed taking into account recombination at the rear surface of the layer. It is demonstrated that, owing to diffusion, excess electrons penetrate deep into the CdTe layer at distances far exceeding the effective penetration length for solar radiation. Calculations of the short-circuit current indicate that, for electron lifetimes of 10−10–10−9 s, typical of thin-film CdS/CdTe solar cells, recombination losses are insignificant if the CdTe layer’s thickness amounts to 3–4 μm but increase dramatically if the thickness is below 1–1.5 μm. In order to eliminate recombination losses in more efficient solar cells where the electron lifetime is ≥10−8 s the absorbing CdTe layer needs to be much thicker.

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