Application of SnO2 substrate to top cell for spectrum splitting type solar cell

We have developed a spectrum splitting type solar cell using a-Si and CIGS as the top and bottom cells, respectively. To increase its performance the top a-Si cell with high Voc and good response at the short wavelength has to be developed. Up to now ZnO has been used as the front TCO. However, since the band gap of ZnO is lower than the one of SnO2, it is better to use SnO2 instead of ZnO. Furthermore, in this splitting solar cell there is no need for front TCO to be much textured. Here we present a initial introduction how to apply commercial and hazy SnO2 to the top cell. Ar treatment has been used in order to flatten the surface of SnO2. As the results high Voc as high as 0.967V has been achieved with smoother SnO2 surface.