Absorptivity of semiconductors used in the production of solar cell panels

The dependence of the absorptivity of semiconductors on the thickness of the absorbing layer is studied for crystalline silicon ($c$-Si), amorphous silicon ($a$-Si), cadmium telluride (CdTe), copper indium diselenide (CuInSe$_2$, CIS), and copper gallium diselenide (CuGaSe$_2$, CGS). The calculations are performed with consideration for the spectral distribution of AM1.5 standard solar radiation and the absorption coefficients of the materials. It is shown that, in the region of wavelengths $\lambda=\lambda_g=hc/E_g$, almost total absorption of the photons in AM1.5 solar radiation is attained in $c$-Si at the thickness $d$ = 7–8 mm, in a-Si at $d$ = 30–60 $\mu$m, in CdTe at $d$ = 20–30 $\mu$m, and in CIS and CGS at $d$ = 3–4 $\mu$m. The results differ from previously reported data for these materials (especially for $c$-Si). In previous publications, the thickness needed for the semiconductor to absorb solar radiation completely was identified with the effective light penetration depth at a certain wavelength in the region of fundamental absorption for the semiconductor.