Surfactant-free CuInSe₂ nanocrystals transformed from In₂Se₃ nanoparticles and their application for a flexible UV photodetector.

In(2)Se(3) nanoparticles were synthesized in an aqueous solution without using any surfactant and then chemically transformed into CuInSe(2) nanocrystals. The transformation was thermodynamically favorable and fast. The 93% production yield in mild reaction conditions allowed mass production of the CuInSe(2) nanocrystals. By the virtue of the surface charges, the CuInSe(2) nanocrystals were well dispersed in polar solvents. The surfactant-free nanocrystals enabled the formation of semiconducting CuInSe(2) films on a flexible polymer substrate without any thermal treatment. We took advantage of this to fabricate a flexible UV photodetector. The current and sensitivity of the devices could be improved by utilizing CuInSe(2) nanocrystals annealed at 160 °C in the reaction batch. On bending test, the detection sensitivity remained the same until the bending radius was reduced down to 4 mm. The dynamic response of the film device was stable and reproducible during light illumination (350 nm).