Formation of Efficient Dye-Sensitized Solar Cells by Introducing an Interfacial Layer of Long-Range Ordered Mesoporous TiO₂ Thin Film

Abstract

Long-range ordered cubic mesoporous TiO 2 films with 300 nm thickness were fabricated on fluorine-doped tin oxide (FTO) substrate by evaporation-induced self-assembly (EISA) process using F127 as a structure-directing agent. The prepared mesoporous TiO 2 film (Meso-TiO 2) was applied as an interfacial layer between the nanocrystalline TiO 2 film (NC-TiO 2) and the FTO electrode in the dye-sensitized solar cell (DSSC). The introduction of Meso-TiO 2 increased J sc from 12.3 to 14.5 mA/cm (2), and V oc by 55 mV, whereas there was no appreciable change in the fill factor (FF). As a result, the photovoltaic conversion efficiency ( eta) was improved by 30.0% from 5.77% to 7.48%. Notably, introduction of Meso-TiO 2 increased the transmittance of visible light through the FTO glass by 23% as a result of its excellent antireflective role. Thus the increased transmittance was a key factor in enhancing the photovoltaic conversion efficiency. In addition, the presence of interfacial Meso-TiO 2 provided excellent adhesion between the FTO and main TiO 2 layer, and suppressed the back-transport reaction by blocking direct contact between the electrolyte and FTO electrode.

Block copolymer-templated synthesis of highly organized mesoporous TiO2-based films and their photoelectrochemical applications

“…Currently various heat-resistant substrates such as Pyrex glass [16,17,45,66], fused silica [51], transparent conductive oxide (TCO) [67][68][69][70][71], quartz [46], stainless steel [72][73][74], Ti foil [50], and silicon [15,75,76] have been employed for film deposition. The nature of coating substrates, particularly the surface roughness, has found to exert an influence on the mesostructural regularity of the mesoporous TiO 2 films [77].…”

“…Generally, the degree of long-range ordering is deteriorated with increase of the substrate roughness. Based on small-angle XRD, TEM and AFM characterizations, Lee's group [45,69,70] have revealed that the long-range ordering of the mesoporous structure may be deteriorated when the substrate is changed from Pyrex glass to FTO and then to ITO conducting glasses. That is, highly organized cubic mesoporous structure was obtained on the smooth Pyrex glass, whereas only worm-like mesoporous structure was formed on the rough ITO glass.…”

“…To overcome the thickness limitations of mesoporous TiO 2 films and to obtain high-efficiency DSSC, Lee and co-workers [70] combined the each advantage of mesoporous films and nanocrystalline TiO 2 layers. As shown in Fig.…”

“…Cross-sectional SEM image of (a) mesoporous TiO2 films (Meso-TiO2) formed on an FTO layer and (b) nanocrystalline TiO2 layer (NC-TiO2)/Meso-TiO2/FTO coating applied to a DSSC; (c) TEM images for the Meso-TiO2 with cubic mesophase deposited on FTO; AFM images (d and e) and transmittance spectra (f) for the surfaces of FTO layer (a) and Meso-TiO2/FTO layer (b and e); spectra (g), electron lifetimes (h), I-V curves (i) for the DSSC with and without interfacial Meso-TiO2[70].…”

A Simple and Highly Efficient Method for Surface Treatment of Ti Substrates for Use in Dye‐Sensitized Solar Cells

“…This result is similar to the FTO-glass-based DSSC after introduction of a highly crystalline blocking layer at the interface of the FTO glass and TiO 2 electrode. [ 34 ] We have introduced a very simple, but highly effective, surface-treatment method for the use of Ti foil as a substrates for photoelectrode in DSSCs. When a Ti substrate was treated with an aqueous HNO 3 -HF solution, both the surface morphology and the crystalline structure of the thermally oxidized layer were varied.…”