Comparative study on effect of titania morphology for light harvesting and scattering of DSSCs: Mesoporous nanoparticles, microspheres, and dandelion-like particles

The light scattering and harvesting effects in dye-sensitized solar cells (DSSCs) is studied by controlling morphology, phase composition, and thickness of monolayer and double-layer TiO₂ photoanode electrodes. The starting materials for preparation of TiO₂ cells, including 25 nm mesoporous anatase nanoparticles, 200 nm anatase microspheres, 10 µm dandelion-like rutile particles and 40 nm nanoparticles containing 80% anatase-20% rutile, are synthesized by evaporation-induced self-assembly, sol-gel, and hydrothermal processes. It was found that the mesoporous anatase nanoparticles may improve light harvesting and dye-sensitization due to their high surface area and small particle size, whereas the microspheres and dandelion-like particles can enhance light scattering effect. The improvement of light harvesting efficiency is obtained by controlling the microstructure and thickness of photoanode electrode to increase dye adsorption. This is achieved by preparation of high surface area TiO₂ monolayer film with optimum thickness and good connections between the particles using mesoporous anatase nanoparticles. The influence of film's thickness on photovoltaic characteristics of monolayer DSSCs shows that the optimal thickness around 30 μm results in the highest cell efficiency of 6.31%. The enhancement of light scattering is acheieved by design of a proper scattering layer with desired morphology and phase composition. The dye loading property of the scattering layer is also considered simultaneously. The photovoltaic characteristics of double-layer DSSCs, with total thickness of 30 µm, reveal that the cell efficiency enhances up to 7.54 and 8.91% using a mixture of dandelion-like particles and mesoporous nanoparticles and microspheres and mesoporous nanoparticles, respectively.