Potential for light trapping in Cu(In,Ga)Se/sub 2/ solar cells

We have analyzed the potential for light trapping in Cu(In,Ga)Se/sub 2/ cells. Key quantities such as back contact reflectance and reflectance at the absorber-window interface are discussed and calculated from measured optical properties. Two model cases, perfectly specular interfaces and Lambertian scattering from the absorber front and back surfaces, are compared in terms of integrated AM 1.5 absorption in the absorber as a function of absorber thickness d/sub a/ for Ag, TiN, Mo back reflectors. Relative to the Mo reflector in the specular model, the potential gain of an Ag reflector at d/sub a/ = 0.5 /spl mu/m is estimated to 2.0 and 3.5 mA/cm/sup 2/ in the specular and scattering cases, respectively. Improved long wavelength quantum efficiency is experimentally demonstrated with a TiN back reflector. The resulting gain in J/sub sc/ is 0.8 mA/cm/sup 2/ at 0.45 /spl mu/m absorber thickness, in accordance with our model results.