Solvothermally synthesized anatase TiO2 nanoparticles for photoanodes in dye-sensitized solar cells

Abstract

Many researchers working on the development of dye-sensitized solar cells (DSCs) continue to focus on the synthesis of photoanode materials with high surface area, along with high light scattering ability to enhance light harvesting efficiency (LHE). Meanwhile, dye packing density, which also impacts the LHE significantly, is often overlooked. Solvothermally synthesized anatase TiO2 nanoparticles (SANP) were obtained by a new and simple approach using a mixed solvent, ethanol and acetic acid. SANP were applied in photoanodes of DSCs using either metal-free organic dye (D149) or organometallic (N719) dyes. Dye loading (packing density) was correlated with the isoelectric point (IEP) in addition to light scattering effects were shown to determine the devices photovoltaic efficiency (PCE); specifically when compared with ones employing commercially available TiO2 nanoparticles. SANP photoanodes sensitized with D149 dye were found to be optimised at 10 µm, yielding a PCE of 6.9%, superior to for transparent or transparent + scattering films from the commercial source (5.6% and 5.9%, respectively). Furthermore, a 7.7% PCE was achieved using a SANP photoanode sensitized with N719 dye, with 7.2% seen for the transparent photoanode and 7.9% with a scattering layer. The high PCEs of of SANP devices are attributed to the high dye loading capability in addition to light scattering. A further point of interest is that even with the increased reactivity of the surface towards dye adsorption, we did not observe any significant increase in recombination with the redox mediator, presumably due to the increased dye loading providing better shielding.