Calculate the wavelength (λ) by this formula, E = hν = hc/λ. Take the bandgap of CdTe/CdS is 1.45eV, because CdTe absorbs the maximum radiation and put other values , then you may find the cutoff value of wave length. solar radiation upto this cutoff value is absorbed by CdTe/CdS.
Basically CdTe/CdS absorb full part of UV, VIS and partial of near IR of solar spectrum.