Suppressing lossy-film-induced angular mismatches between reflectance and transmittance extrema: Optimum optical designs of interlayers and AR coating for maximum transmittance into active layers of CIGS solar cells

The investigation of optimum optical designs of interlayers and antireflection (AR) coating for achieving maximum average transmittance (T _ave) into the CuIn_1-xGa_xSe₂ (CIGS) absorber of a typical CIGS solar cell through the suppression of lossy-film-induced angular mismatches is described. Simulated-annealing algorithm incorporated with rigorous electromagnetic transmission-line network approach is applied with criteria of minimum average reflectance (R _ave) from the cell surface or maximum T_ave into the CIGS absorber. In the presence of one MgF2 coating, difference in R_ave associated with optimum designs based upon the two distinct criteria is only 0.3% under broadband and nearly omnidirectional incidence; however, their corresponding T_ave values could be up to 14.34% apart. Significant T_ave improvements associated with the maximum-T_ave-based design are found mainly in the mid to longer wavelengths and are attributed to the largest suppression of lossy-film-induced angular mismatches over the entire CIGS absorption spectrum. Maximum-T_ave-based designs with a MgF ₂ coating optimized under extreme deficiency of angular information is shown, as opposed to their minimum-R_ave-based counterparts, to be highly robust to omnidirectional incidence.