Transition from photoconductivity to photovoltaic effect in P3HT/CuInSe ₂ Composites

We report the investigation of composites of poly-(3-hexylthiophene) (P3HT) and CuInSe ₂ nanocrystals (NCs). CuInSe ₂ 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 CuInSe ₂ NCs. The results suggest that nanocrystal-polymer charge transfer is foreseeable in the P3HT and CuInSe ₂ system because of their type II band alignment. We studied optical properties of the hybrid composite films of P3HT and CuInSe ₂ NCs as a function of P3HT/CuInSe ₂ NCs weight ratios. The quenching of photoluminescence spectra with the increase of CuInSe ₂ ratio in the composite was interpreted to result from charge transfer between the polymer and CuInSe ₂ NCs. We further studied photodiode devices that exhibited a transition from photoconductive gain to the photovoltaic effect with an increase of the P3HT/CuInSe ₂ weight ratio. Performance of the photovoltaic devices was strongly limited by intrinsic traps associated with the CuInSe ₂ NCs.