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

In2Se3 nanoparticles were synthesized in an aqueous solution without using any surfactant and then chemically transformed into CuInSe2 nanocrystals. The transformation was thermodynamically favorable and fast. The 93% production yield in mild reaction conditions allowed mass production of the CuInSe2 nanocrystals. By the virtue of the surface charges, the CuInSe2 nanocrystals were well dispersed in polar solvents. The surfactant-free nanocrystals enabled the formation of semiconducting CuInSe2 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 CuInSe2 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).