Efficiency improvement of flexible dye-sensitized solar cells by introducing mesoporous TiO2 microsphere

Mesoporous TiO₂ microsphere (MTM) was synthesized via a simple solution route and then mixed with commercial TiO₂ (P25) to form highly homogeneous and stable TiO₂ colloid by simple hydrothermal treatment. The TiO₂ colloid was coated onto the plastic conductive substrate to prepare mesoporous TiO₂ film for flexible dye-sensitized solar cells (DSSCs) by low-temperature heat treatment. The influence of MTM content on the physicochemical properties of the flexible TiO₂ film was characterized by scanning electron microscope, transmission electron microscopy, X-ray diffraction, energy-dispersive X-ray spectrometer, N₂ adsorption-desorption isotherms, UV-vis absorption and diffuse reflectance spectra. It is revealed that with increasing the MTM content, the dye-loading capability of TiO₂ film and light-harvesting efficiency of flexible DSSCs are improved due to MTM having high surface area and acting as a light scattering center, respectively, resulting in the enhancement of photocurrent of flexible DSSCs. However, more and larger cracks having negative effect on the performances of flexible DSSCs are formed simultaneously. Under the optimal condition with MTM content of 20%, a flexible DSSC with overall light-to-electric energy conversion efficiency of 2.74% is achieved under a simulated solar light irradiation of 100 mW cm^?2 (AM 1.5), with 26% improvement in comparison with DSSCs based on P25 alone.