A Quantitative Study of ZnO Materials as Possible Down-shifters for Solar Cell Applications

We report about a systematic study of nanocrystalline ZnO which exhibits intensive blue-green defect luminescence after annealing in reducing atmosphere. The ZnO has been dispersed in a polymer and tested with a commercial Si solar cell. A quantitative model including photoluminescent quantum efficiency, absorption and backscattering has been developed and compared with measurements of the ZnO-coated cell. We find that strong backscattering from the ZnO layer leads a reduced efficiency of the system except for a small enhancement in the UV region. Necessary conditions for achieving overall improvements in cell efficiency are derived.