Dual functionalized freestanding TiO₂ nanotube arrays coated with Ag nanoparticles and carbon materials for dye-sensitized solar cells

Highly ordered, freestanding TiO₂ nanotube arrays (TiO₂ NTAs) were prepared using an electrochemical method. The barrier layer was etched to open the bottom of each array, aptly named "open-ended TiO₂ NTAs". These arrays were coated with silver nanoparticles (Ag NPs) and/or carbon materials to enhance electron generation and transport. The energy conversion efficiency of the resulting dye-sensitized solar cells (DSSCs) with open-ended freestanding TiO₂ NTAs, when coated with Ag NPs, increased from 5.32% to 6.14% (by 15%) due to plasmonic interactions. Meanwhile, coating the open-ended freestanding TiO₂ NTAs with carbon materials increased the energy conversion efficiency from 5.32% to 6.07% (by 14%), due to π-π conjugation. When the Ag NPs and carbon materials were simultaneously applied to the open-ended freestanding TiO₂ NTAs, the energy conversion efficiency increased from 5.32% to 6.91%-an enhancement of 30%, due to the additive effects of plasmonics and π-π conjugation.