Transition from Photoconductivity to Photovoltaic Effect in P3HT/CuInSe2 Composites

We report the investigation of composites of poly-(3-hexylthiophene) (P3HT) and CuInSe2 nanocrystals (NICs). CuInSe2 NCs were synthesized at gram scale through a colloidal route. Cyclic voltammetry was used to determine the HOMO-LUMO energy levels, as well as the energies of trap states intrinsic to CuInSe2 NCs. The results suggest that nanocrystal-polymer charge transfer is foreseeable in the P3HT and CuInSe2 system because of their type II band alignment. We studied optical properties of the hybrid composite films of P3HT and CuInSe2 NCs as a function of P3HT/CuInSe2 NCs weight ratios. The quenching of photoluminescence spectra with the increase of CuInSe2 ratio in the composite was interpreted to result from charge transfer between the polymer and CuInSe2 NCs. We further studied photodiode devices that exhibited a transition from photoconductive gain to the photovoltaic effect with an increase of the P3HT/CuInSe2 weight ratio. Performance of the photovoltaic devices was strongly limited by intrinsic traps associated with the CuInSe2 NCs.