Precise Preparation of CdS Thin Films for Efficient Sb2S3–ySey Thin-Film Solar Cells

Abstract

In this work, CdS thin films were prepared by chemical bath deposition (CBD) and Sb2S3–ySey thin films were prepared by a hydrothermal method. Solar cells with the architecture of FTO/CdS/Sb2S3–ySey/spiro-OMeTAD/Au were fabricated to evaluate the quality of CdS thin films as the electron transport layer. The precise preparation strategy with the combination of adjusting the thickness of CdS thin films prepared by CBD and changing the concentration of the CdCl2 methanol solution in the post-treatment process was first proposed. When the CdS thin-film thicknesses were 100, 80, 65, and 40 nm and the CdCl2 methanol solution concentration was 20 mg·mL–1, the power conversion efficiencies (PCEs) of the corresponding solar cells were 7.32% of 100 nm, 7.62% of 80 nm, 8.00% of 65 nm, and 7.55% of 40 nm. When the CdS thin-film thickness was 40 nm and the CdCl2 methanol solution concentrations decreased to 15, 13.3, 10, and 5 mg·mL–1, the PCEs were 7.98% of 15 mg·mL–1, 8.46% of 13.3 mg·mL–1, 7.71% of 10 mg·mL–1, and 7.31% of 5 mg·mL–1. Therefore, the 40 nm thick compact and full-coverage CdS thin film without the appearance of residual CdCl2 can be successfully obtained using the precise preparation strategy and achieved an optimal PCE of 8.46%. The precise preparation strategy is also valuable to develop the ultrathin, compact, and full-coverage CdS thin film as the electron transport layer for CdTe thin-film solar cells.