High-Performance Large-Scale Flexible Dye-Sensitized Solar Cells Based on Anodic TiO₂ Nanotube Arrays

A simple strategy to fabricate flexible dye-sensitized solar cells involves the use of photoanodes based on TiO₂ nanotube (TNT) arrays with rear illumination. The TNT films (tube length ∼35 μm) were produced via anodization, and sensitized with N719 dye for photovoltaic characterization. Pt counter electrodes of two types were used: a conventional FTO/glass substrate for a device of rigid type and an ITO/PEN substrate for a device of flexible type. These DSSC devices were fabricated into either a single-cell structure (active area 3.6 × 0.5 cm²) or a parallel module containing three single cells (total active area 5.4 cm²). The flexible devices exhibit remarkable performance with efficiencies η = 5.40 % (single cell) and 4.77 % (parallel module) of power conversion, which outperformed their rigid counterparts with η = 4.87 % (single cell) and 4.50 % (parallel model) under standard one-sun irradiation. The flexible device had a greater efficiency of conversion of incident photons to current and a broader spectral range than the rigid device; a thinner electrolyte layer for the flexible device than for the rigid device is a key factor to improve the light-harvesting ability for the TNT-DSSC device with rear illumination. Measurements of electrochemical impedance spectra show excellent catalytic activity and superior diffusion characteristics for the flexible device. This technique thus provides a new option to construct flexible photovoltaic devices with large-scale, light-weight, and cost-effective advantages for imminent applications in consumer electronics