Studying the charge carrier properties in CuInS2 films via femtosecond transient absorption and nanosecond transient photocurrents**Project supported by the National Natural Science Foundation of China (Grant Nos. 21573094, 51502109, 11774122, 11574112, and 11474131), the National Found for Fostering Talents of Basic Science, China (Grant No. J1103202), and the China Scholarship Council (CSC) obtained during the visit of Ning Sui to

Abstract

The carrier behavior in CuInS2 thin films at femtosecond and microsecond time scales is discussed in detail. Transient absorption data suggests that the photo-generated carriers relax rapidly accompanied by a change in energy. The photo-generated charge carriers are extracted by a bias electric field E in the nanosecond transient photocurrent system. An applied E improves the efficiency of photon conversion to charge carriers and enhances the velocity of the extracted charge carriers. In addition, there exists a threshold of illumination intensity in the extraction process of charge carriers in the CuInS2 thin film, above which carrier recombination occurs. The corresponding loss further increases with illumination intensity and the recombination rate is almost independent of E. Our results provide useful insights into the characteristics of carriers in the CuInS2 thin film and are important for the operation of optoelectronic devices realized with these films.