Optical absorption of thin film on a Lambertian reflector substrate

A formula is derived for calculating the optical absorption of thin films deposited on a Lambertian reflector substrate. It is shown that compared with the case of flat reflecting substrate, the incoherent absorption is enhanced by a factor of in the weak absorption limit, where ε1is the real part of the film dielectric constant and is a slightly varying function of ε1. For a 0.5-µm a-SiHx(bandgap 1.7 eV) solar cell with a Lambertian reflector substrate, the total absorption in terms of the short-circuit current is calculated to be 18.63 mA/cm².