Cu‐In‐S precursor films were deposited at various substrate temperatures by pulsed laser deposition (PLD). CuIn(S,Se)2 films were prepared by post‐annealing the Cu‐In‐S precursor films in H2S and Se atmosphere. CuIn(S,Se)2 solar cells with a device structure of Au/ITO/i‐ZnO/CdS/CuIn(S,Se)2/Mo/soda‐lime (SLG) glass were fabricated and characterized. Higher conversion efficiency was obtained for the CuIn(S,Se)2 solar cell with the precursor film deposited at room temperature. The phase and microstructure of the Cu‐In‐S precursor and the annealed CuIn(S,Se)2 films were examined by X‐ray diffraction (XRD) and scanning electron microscopy (SEM). We found that the quality of the CuIn(S,Se)2 films was strongly affected by the deposition temperature of Cu‐In‐S precursor films. We discuss the grain growth and sintering in CuIn(S,Se)2 films on the basis of the results of XRD and SEM. The highest conversion efficiency of 6.38% (Voc = 521 mV, Jsc = 22.6 mA cm−2, FF = 0.541) was obtained for the CuIn(S,Se)2 solar cell with the precursor film deposited at room temperature and post‐annealed at 620 °C. The solar cell was analyzed by secondary ion mass spectroscopy (SIMS) and transmission electron microscopy (TEM).

For applications to polycrystalline thin-film tandem solar cells, we studied p-type conductive BaCuSF single layer and p-type BaCuSF and n-type In 2 O 3 :Sn (ITO) bilayer films. The BaCuSF films were prepared by pulsed laser deposition (PLD), and the ITO films were prepared by RF sputtering. The bilayer film showed ohmic current-voltage characteristic. A tunnel junction between these two layers was successfully fabricated, because p-type BaCuSF and n-type ITO layers had sufficiently high carrier concentrations. The BaCuSF/ITO bilayer films were employed as the back electrodes of CdS/CdTe solar cells. A CdTe solar cell with a 20-nm-thick BaCuSF/a 300-nm-thick ITO bilayer back contact showed a high conversion efficiency of 13.9% (V OC = 818 mV, J SC = 25.2 mA/cm 2 , and FF = 0.675), which was higher than that of a CdTe solar cell with a BaCuSF single-layer back contact (11.1%). The efficiency is comparable to that of a CdTe solar cell with a SrCuSeF/ITO bilayer back contact (14.3%).