Submicrometer@nano Bimodal TiO2 Particles as Easily Sintered, Crack-Free, and Current-Contributed Scattering Layers for Dye-Sensitized Solar Cells

Abstract

Submicrometer@nano bimodal TiO2 particles consisting of a submicrometer core and a mesoporous structured shell were synthesized by a chemical deposited method. The submicrometer TiO2 particles were first dispersed in the titanium(IV) bis(ammonium lactato) dihydroxide solution in the presence of polyethyleneimine and urea; after reflowing hydrolysis, the suspension was transferred to a Teflon autoclave and subjected to hydrothermal treatment at 150 °C for 24 h. The as-prepared nanocrystal-coated submicrometer TiO2 (NCS-TiO2) showed a core/shell structure where the outer TiO2 nanocrystals with the size of 5 to 7 nm and in anatase phase uniformly coated on the submicrometer TiO2. When the NCS-TiO2 was fabricated as the scattering layer in dye-sensitized solar cells (DSSCs), it adsorbed more dye molecules while still keeping a high light-harvesting efficiency. Moreover, the presence of TiO2 nanocrystals in NCS-TiO2 reduced the sintering stress between the transparent porous layer and the scattering layer, leading to a crack-free and high-quality photoanode film, which also reduced the serial resistance, as verified by electrochemical impedance spectroscopy. Finally, DSSCs with the NCS-TiO2 scattering layer reached an efficiency of 8.36%, which showed a 20% improvement compared with the one without it.