Akira Hanafusa

16.0% Efficient Thin-Film CdS/CdTe Solar Cells

High efficiency cadmium sulfide (CdS)/cadmium telluride (CdTe) solar cells have been developed using ultrathin CdS films having a thickness of 50 nm. CdS films deposited on indium tin oxide (ITO)/#1737 glass substrates by the metal organic chemical vapor deposition technique, and CdTe films subsequently deposited by the close-spaced sublimation technique were used for the fabrication of CdS/CdTe solar cells. A photovoltaic conversion efficiency of 16.0% under Air Mass (AM) 1.5 conditions has been measured by the Japan Quality Assurance Organization.

Performance of Graphite Pastes Doped with Various Materials as Back Contact for CdS/CdTe Solar Cell

To date the problem of developing a suitable back contact for CdS/CdTe solar cells has yet to be resolved. The Cu-doped graphite paste that is widely used as a back contact is associated with degradation problems due to possible Cu diffusion across the CdS/CdTe junction. This study was designed to find ways to improve the graphite paste for superior electrical contacts. Mixtures of graphite paste with various material constituents and dopants consisting of silver-, lead-, nickel-, antimony-, bismuth-, or phosphor-based compounds, were studied. Results show that the performances of solar cells fabricated from these graphite pastes vary with the change in the composition. In the cases of Ag2Te and Ni2P, we studied their relationship with the solar cell characteristics with regard to dopant quantity, and furthermore in the case of Ag2Te, with regard to the sintering temperature of the graphite electrode. A fill factor (F.F.) of over 0.65 and efficiencies over 13% were obtained with Ag2Te, Ag3PO4, Ag2MoO4, and NiTe, and efficiencies over 12% were obtained with AgF, AgCl, Ni2P, and Ni3P.