Nanocrystalline copper indium selenide (CuInSe₂) particles for solar energy harvesting

High quality copper indium selenide (CuInSe₂) nanocrystals were synthesized solvothermally at low temperature (180°C) using selenite salts (SeO₃^2-) as a dual source for metal and chalcogen, and dimethylformamide (DMF) as one of the solvents and the reducing agent. In order to find out the best solvent combinations for this type of reduction reaction, the effects of different co-solvents on the phase and morphology of the final products were studied in detail. Pure phase CuInSe₂ with high crystallinity was synthesized in a methanol-DMF (Me-DMF) system. On the other hand, using water-DMF (H₂O-DMF) resulted in some impurity and nanocrystals of poor crystallinity. Raman study revealed that CuInSe₂ crystals synthesized in Me-DMF and H₂O-DMF exhibit different scattering geometries. The difference of the final products obtained from Me-DMF and H₂O-DMF systems may be due to the difference in the reducing ability of methanol and water as well as the difference in the interaction force between the two solvents within each system. Different morphologies such as nanoparticles and nanoplates can be obtained by simply varying the precursor concentration in the mixed solvents. The photo-response of the as-synthesized materials in a 3-electrode photo-electrochemical (PEC) cell suggests that these materials have the potential to be used for solar energy harvesting.