真空蒸着によるＣｄＳ（Ｃｕ）／ＣｄＳ薄膜光電池の作成と効率の基板温度依存性

Abstract

Thin-film photovoltaic cells composed of Cu-doped CdS and non-doped CdS layers (SnO2/CdS (Cu) /CdS/A1) have been fabricated by an all vacuum deposition process. First, thin Cu film (about 10 nm thick) was deposited on the SnO2 coated glass substrate followed by the deposition of CdSI layer (about 500 nm thick). These layers were annealed in a vacuum at 350°C for 15 min. before the deposition of CdSII layer (about 4 pm thick). The substrate temperature was lowered from 200°C to 130°C and held at 130°C during deposition of CdSII layer. This process was most important to get efficient cells. Finally, Al film was deposited on the CdSII layer as a counter electrode. The conversion efficiency of the best cell was over 7%. Depth profiles measured by SIMS showed that the Cu diffused into CdSII layer through CdSI layer and the diffusion of Cu slowed down drastically at a substrate temperature of about 140°C and stopped at about 130°C. As a result, the boundary between the Cu-doped p-type CdS layer and non-doped CdS layer was formed in the CdSII layer. The spectral responses of the short-circuit current of the cells were mainly dominated by the band gap energy and Cu impurity levels in CdS. Therefore, we concluded that the photovoltaic effect of the cells was caused by the p-i-n or p-n homojunction of CdS.