Quasi-monodispersed anatase TiO₂ submicrospheres as current-contributed scattering particles for dye-sensitized solar cells

Graphical abstract: Anatase TiO₂ submicrospheres with high surface area were prepared and used for the scattering layer of DSSCs, leading to an efficiency from 7.24% to 9.07%. - Highlights: • TiO₂ submicrospheres (200 nm) with a high surface area were prepared by the hydrothermal method from Ti(SO₄)₂ and (NH₄)2SO₄ solution. • By using TiO₂ submicrosphere scattering particles on top of semitransparent layer, the power conversion efficiency of DSSCs improved to 9.07%. • Relationship between the efficiency with EIS interfacial resistance of DSSC under 0.1 to 1.0 sun irradiation was analyzed. - Abstract: Hierarchical anatase TiO₂ submicrospheres were synthesized by direct hydrothermal method at 120 °C using Ti(SO₄)₂ and (NH₄)₂SO₄ mixed solution as precursor. The calcined spheres in particle size of 150–200 nm, which consisted of closely connected nanocrystals in a crystallite size of about 24.2 nm and had a relatively high specific surface area of 43.2 m² g⁻¹ compared to microspheres. In presence of TiO₂ submicrospheres as the scattering layer on top of semitransparent layer, the power conversion efficiency of dye-sensitized solar cells (DSSCs) was increased to as high as of 9.07% from 7.24%. This remarkable improvement compared to commercial scattering particles (efficiency of 8.33%) is mainly attributed to their higher surface area for increasing the loading of dye molecule as well as a lower resistance under 1 sun irradiation. The relationship between the conversion efficiency of DSSCs with interfacial resistance under 0.1 to 1.0 sun illumination was further investigated, the decrease of the light power density led to the increase of interfacial resistance. Moreover, even under 0.1 sun irradiation, DSSC still had an efficiency of 7.18% but a slightly lower V_oc of 0.597 V.