Development of multilayer back reflectors for improved a-Si based solar cell performance

A new back reflector comprised of an Al/(multi-layered stack)/ZnO structure is being developed to replace Al/ZnO used in manufacturing and boost conversion efficiencies with improved back reflector performance. Use of the multi-layered stack should lead to improved reflectivity that will in turn improve solar cell currents and efficiencies. Using TCOs with low indices of refraction between 1.6 and 1.7, AI(specular)/ML/ZnO back reflectors have been fabricated with reflectance values in the red portion of the light spectrum (600-1000 nm) that are close to those obtained with the AI/MgF₂/Si/MgF₂ optical stacks and Ag/ZnO back reflectors. With the AI(specular)/ML/ZnO back reflector stacks, a 1.7 mA/cm² improvement in the red light short circuit current has been obtained for a-SiGe cells. However, the gain in red light efficiency is not as large as expected with textured back reflectors. Improvements should come through re-optimization of the multi-layer stack or use of different texturing schemes.