CuInS2 thin film with flat surface by crystalization of Cu-In-S precursor

CuInS₂ (CIS) films used in the absorber layer of solar cells are often prepared by the sulfurization of Cu-In metallic precursors. The CIS films usually show large surface roughness, which would decrease the open-circuit voltage of the solar cell because of a large np junction area and insufficient surface coverage of buffer layers. In this study, Cu-In-S precursors were deposited at the low temperature of 50°C and the films were subsequently annealed to promote crystal growth at the high temperature of 500~600°C with sulfur supply. The annealed films successfully showed flat surface morphology and large crystal grain size of around 1 μm which was comparable to that of the CIS films prepared by the sulfurization of Cu-In metallic precursors. The root-mean-square roughness of 60 nm was smaller compared to that of the CIS films fabricated by the sulfurization of the Cu-In metallic precursors of 210 nm and comparable to that of Cu(In, Ga)Se₂ films used in high efficiency solar cells.