TiO₂nanotube membranes on transparent conducting glass for high efficiency dye-sensitized solar cells

Abstract

Crack-free TiO(2) nanotube (NT) membranes were obtained by short time re-anodization of a sintered TiO(2) NT array on Ti foil, followed by dilute HF etching at room temperature. The resulting freestanding TiO(2) membranes were opaque with a slight yellow color having one end open and another end closed. The membranes were then fixed on transparent fluorine-tin-oxide glass using a thin layer of screen-printed TiO(2) nanoparticles (NPs) as a binding medium. It was found that low temperature treatment of the resulting NT/NP film under appropriate pressure before sintering at 450 °C was critical for successful fixation of the NT membrane on the NP layer. The resulting films with open-ends of NT membranes facing the NP layer (open-ends down, OED, configuration) exhibited better interfacial contact between NTs and NPs than those with closed-ends facing the NP layer (closed-ends down, CED, configuration). The cells with an OED configuration exhibit higher external quantum efficiency, greater charge transfer resistance from FTO/TiO(2) to electrolyte, and better dye loading compared to CED configurations. The solar cells with the OED configuration gave 6.1% energy conversion efficiency under AM1.5G condition when the commercial N719 was used as a dye and I(-)/I(3)(-) as a redox couple, showing the promise of this method for high efficiency solar cells.

Comparison of Anodic TiO2‐Nanotube Membranes used for Frontside‐Illuminated Dye‐Sensitized Solar Cells

“…Different approaches have been reported to accomplish successful detachment of the tube arrays from the metal substrate, and the transferred TiO 2 nanotube layers have been explored in DSSCs in various configurations (tube bottom up/down and open/close tube bottom) [15][16][17][18][19][20][21].…”

“…given by the tube bottom is minimized (clearly, this refers to the case when a front side irradiation geometry is adopted) [17]; and ii) more efficient charge transport and collection are obtained when the tub top is in contact with the TiO 2 NP layer.…”

Enhanced light-harvesting of the conical TiO 2 nanotube arrays used as the photoanodes in flexible dye-sensitized solar cells

“…Till now, more researches have been devoted to fabricate the free-standing TiO 2 nanotube arrays (NTAs) used in DSSCs [24][25][26]. As they are normally grown on the Ti foil by anodic oxidation process, and they are only used as the back-illuminated photoanodes in DSSCs, while the light scattering from the Pt photocathodes will induce some losses of the irradiated sun light.…”

“…As they are normally grown on the Ti foil by anodic oxidation process, and they are only used as the back-illuminated photoanodes in DSSCs, while the light scattering from the Pt photocathodes will induce some losses of the irradiated sun light. Recently, TiO 2 NTAs were successfully transferred and fixed on transparent fluorine-tin-oxide (FTO) glass using a thin layer of TiO 2 nanoparticles (NPs) as a binding medium [26], and then the samples were sintered at 450 C to remove the organic binder to fix a TiO 2 membrane on FTO closely. Therefore, it provides a good route to transfer the prepared TiO 2 NTAs on the flexible polyethylene naphthalate (PEN) substrates coated indium tin oxide (ITO), which may realize the fabrication of the frontilluminated flexible DSSCs.…”

Enhanced performance of dye-sensitized solar cells based on TiO2nanotube membranes using an optimized annealing profile

“…To date the latter approach, that is, the layer transfer, led to higher cell performance compared to sputtering Ti layers on FTO. [18][19][20] A range of different strategies were developed for transferring and arranging tube membranes for their use in DSSCs. Not only tube length and various decoration techniques but also different geometries and configurations, such as open/closed tube bottom and tube bottom up/down (illustrated in Scheme S1 in the ESI †), were explored.…”