Spray-deposited CuInS2 solar cells

Spray deposition of CuInS2 offers an attractive route towards industrial production of thin-film solar cells. With spray deposition it is possible to make nanocomposites of n-type TiO2 and p-type CuInS2. Upon application of an In2S3 buffer layer, solar cells can be made with efficiencies of similar to 7%, being comparable to that of amorphous silicon. Rapid thermal annealing is not involved in the production of these solar cells. In order to further improve the performance, the concentration of electronic defect states in the bandgap must be reduced. Towards this end a detailed study has been undertaken to elucidate the role of associated point defects in the recombination of electron-hole pairs. Especially with transient absorption spectroscopy it is possible to make an accurate assessment of the fundamental electronic processes that are involved. We find electronic states in the bandgap related to the presence of anti-site defects. In addition, indium vacancies are also involved. State-to-state recombination occurs, indicating that the involved defects are associated. An electronic state located at 1.1 eV above the valence band, which is related to indium on a copper position, has a lifetime of about 20 mu s at room temperature. The lower lying states related to copper on indium positions, and indium vacancies, are populated from this 1.1 eV state.