Microwave-assisted hydrothermal synthesis of TiO₂ spheres with efficient photovoltaic performance for dye-sensitized solar cells

In this article, we present a microwave-assisted synthetic method to form micrometer size mesoporous TiO₂ sphere for the application as photoanodes in dye-sensitized solar cells (DSCs). The material properties and photovoltaic performances are compared with commercial TiO₂ paste and mesoporous sphere both fabricated by traditional hydrothermal method. The mesoporous TiO₂ spheres were synthesized by controlled hydrolysis and subsequently grew with microwave heating. The microwave-synthesized mesoporous TiO₂ spheres with diameters in the range from 400 to 600 nm are composed of 10 nm nanocrystals as building blocks and possess anatase crystal structure and high surface area (132.49 m² g^-1). The photovoltaic performances of DSCs using the photoanodes derived from hydrothermal mesoporous spheres and the microwave-synthesized mesoporous spheres yielded overall power conversion efficiencies of 5.89 and 5.43 % with the less volatile 3-methoxypropionitrile solvent electrolyte. The reaction time for crystallization process in the microwave heating was greatly shortened from 16 h to 80 min. The microwave-synthesized mesoporous spheres exhibit higher short-circuit photocurrent than commercial available hydrothermal nanocrystalline (JGC 18NRT). This is due to its superior scattering power in the entire visible and near-infrared regions, which enhanced the optical path in the photoactive medium. The incident photon to electron conversion efficiency results reflect that the better short-circuit current in the device made with microwave-synthesized mesoporous spheres electrodes is resulted from the increased light-harvesting efficiency in the red region. On the optimum condition with acetonitrile-based electrolyte, the microwave-synthesized mesoporous spheres electrode could deliver conversion efficiency of 6.19 % and higher value of 6.92 % by adding extra scattering layer of commercial paste (CCIC, HPW-400).