Investigations of the polymer alignment, the nonradiative resonant energy transfer, and the photovoltaic response of poly(3-hexylthiophene)/TiO(2) hybrid solar cells

Abstract

We report the effects of annealing on the performance of hybrid photovoltaic (PV) cells containing poly(3-hexylthiophene) (P3HT) coated onto TiO(2)/Sn doped In(2)O(3) (ITO) and ITO substrates. In the optimized device, which exhibits a higher efficiency, the backbone axes of the P3HT chains were found to lie within the substrate plane, their conjugated planes are slightly tilted, and their side chains are substantially tilted. The carboxylate group is attached via bidentate or bridging coordination to the TiO(2) surface and enables photoinduced charge transfer between TiO(2) and P3HT. The observed large quenching (with excitation at 488 nm) and enhanced emission (with excitation at 325 nm) indicates that efficient Forster resonance energy transfer occurs between TiO(2) and P3HT. Thus, the main influences on the high efficiency of the hybrid PV cells are the photon-mediated electronic transition and the photoinduced charge transfer.