Surface Morphology and Device Performance of CuInS 2 Solar Cells Prepared by Single- and Two-Step Evaporation Methods

Absorbers of CuInS 2 (CIS) solar cells are fabricated by several processes and a 11.4% efficiency CIS solar cell is reported. However, this value is lower than the theoretically expected value, possibly owing to the roughness of the CIS surface. In this study, we attempted to realize smoother CIS films using a new two-step evaporation method. As a first step, Cu-rich CIS films were deposited at a low substrate temperature of 50 °C and were annealed at 500 °C. As a second step, In and S were sequentially deposited on the annealed films to control the compositional ratio to In-rich. The deposited film showed a smoother surface than the film deposited by the single-step evaporation of Cu, In, and S. The CIS solar cell formed using the two-step evaporation method showed a higher open-circuit voltage. This should be due to the smoother film surface, which reduced the p–n junction area of the device.