Sensitization of Hydrothermally Grown Single Crystalline TiO₂ Nanowire Array with CdSeS Nanocrystals for Photovoltaic Applications

An oriented array of electron transporting nanowires, grown directly on a transparent conductor constitutes an optimal architecture for efficient photovoltaic applications. In addition, semiconductor nanocrystals can work as efficient light absorbers because of their tunable optical properties. In this paper, we use an oriented array of TiO₂ nanowires grown directly on a transparent conductive electrode and subsequently sensitized with colloidally grown CdSeS nanocrystal quantum dots (QDs), using an efficient bi-linker assisted methodology, to demonstrate photovoltaic cells. Upon excitation with light, exciton dissociation takes place at the nanowire-nanocrystal interface, after which, electrons are transported to the fluorine-doped tin oxide (FTO) electrode via single-crystalline TiO₂ nanowire channels. We demonstrate that an ex situ ligand exchange of QDs followed by sensitization on oxygen-plasma treated TiO₂ nanowires results in enhanced loading of QDs, as compared to the in situ ligand exchange approach. An array of 1 μm long TiO₂ nanowire sensitized with CdSeS nanocrystals exhibits photovoltaic effects with a short-circuit current of 2–3 mA/cm², an open circuit voltage of 0.6–0.7 V and a fill factor of 52–65%, resulting in devices with efficiencies of up to 0.6%.