Synthesis and Ultrafast Carrier Dynamics of Single-Crystal Two-Dimensional CuInSe<sub>2</sub> Nanosheets

2015-12-17T03:56:35Z (GMT) by Xin Tao Elham Mafi Yi Gu
We report, for the first time, the synthesis of single-crystal two-dimensional (2D) CuInSe<sub>2</sub> nanosheets and the studies of ultrafast carrier dynamics and transport in this 2D material. Particularly, single-crystal 2D CuInSe<sub>2</sub> with various thicknesses in the nanometer regime were fabricated by a solid-state chemical reaction between Cu and single-crystal exfoliated In<sub>2</sub>Se<sub>3</sub> nanosheets. Characteristics of transient optical reflectivity, obtained from femtosecond optical pump–probe measurements on single CuInSe<sub>2</sub> nanosheets, suggest that the hot carrier cooling process dominates the carrier dynamics within a few picoseconds following the optical excitation. Spatially resolved pump–probe measurements, coupled to simple model calculations, were used to obtain the ambipolar hot carrier diffusion coefficient in single nanosheets. The dependence of the hot carrier diffusion coefficient on the nanosheet thickness provides insight into the limiting mechanisms of hot carrier transport and can be used to gauge the possibility of efficient hot carrier collection in nanostructured CuInSe<sub>2</sub> solar cells.