A Comparative Study of Organic Dye-Sensitized Solar Cells Based on Anatase TiO2 and Amorphous Free Mixed Phase’s Anatase/Rutile P25 TiO2 Photoanodes

Dye-sensitized solar cells (DSCs) remain an interesting photovoltaic concept, although recent times have seen their envisioned broad-scale applications being replaced with more niche ones. Nevertheless, as a key component of DSCs, titanium(IV) oxide (TiO2) must be produced in a large volume, low cost, and highly reproducible manner. Degussa P25 remains a benchmark TiO2 product, addressing the first two of the above points very well. Post-treatment processes that may also be carried out on a large scale give some hope to addressing the reproducibility issue. This paper builds on our previous works wherein mixed-phase P25 (anatase + rutile + amorphous TiO2) was converted into an amorphous free form by selectively dissolving and recrystallizing the amorphous component. Here we investigated the performance of metal-free organic dye (D149)-based DSCs with three different TiO2 films: (1) as-received P25 (TiO2-P25), (2) amorphous-free P25 (TiO2-HP25), and (3) anatase nanoparticles obtained from Dyesol (TiO2-DSL). DSCs based on TiO2-HP25 showed comparable performance (5.8 ± 0.2% PCE) to DSCs based on the TiO2-DSL (5.8 ± 0.4% PCE) and substantially higher than for devices based on the as-obtained P25 nanoparticles (3.9 ± 0.4% PCE). The enhancement resulting from the post-processing of P25 derives from simultaneous increases in photo-current density (Jsc), open-circuit voltage (VOC), and the fill factor (FF), due to enhancing the dye-loading capability and the charge-transport efficiency (suppressing the electron recombination) as a result of the removal of amorphous barriers and associated defect states. This is in line with enhancing DSC performance based on the organometallic N719 dye we reported previously. However, the photoanode material based on abundant P25 TiO2 sensitized with high-extinction-coefficient organic D149 dye can be adopted as a cost-effective DSC as an alternative to relatively high-cost DSCs based on the commercial anatase TiO2 sensitized with organometallic N719 dye.