Effect of substrate temperatures on evaporated In2S3 thin film buffer layers for Cu(In,Ga)Se2 solar cells

• In2S3 films were deposited at various substrate temperatures by thermal evaporation.
• The atomic ratio of In to S in the In2S3 film has the highest value at 300 °C.
• The In2S3 film has a band gap of about 3.8 eV because of its amorphous structure.
• The In2S3 film is expected to be used as a buffer layer by in-line vacuum process.

For the realization of vacuum in-line process in the fabrication of Cu(In,Ga)Se2 (CIGS) solar cells, In2S3 thin film buffer layers for CIGS have been deposited on glasses and CIGS layers with a thickness of about 650 Å by thermal evaporation process. During the thermal evaporation, the temperature of the substrate was varied from room temperature to 500 °C by heating and the grown In2S3 films were investigated and analyzed in terms of the optimized buffer layer for CIGS solar cells. From the results of scanning electron microscope and X-ray diffraction, the In2S3 thin film deposited at a higher substrate temperature showed the larger grain size and the films have amorphous structural characteristics. Although the structural characteristics such as the atomic ratio of In to S and transmittance of the In2S3 thin films were not proportional to temperature, it was possible to obtain the large optical band gap of In2S3 films of about 3.8–3.9 eV enough to be used as the buffer layer of CIGS.