Fabrication and Characterization of Solid-State Dye Sensitized Solar Cells using Hollow Microsphere TiO2 Layers

We fabricated dye sensitized solar cells using hollow microsphere TiO2 photoelectrode made by polystyrene (PS) nanoparticle embedded TiO2 paste. This made significant improvement on the efficiency and short-circuit current of DSSCs. Two different sizes of PS nanoparticles were used, 400 nm and 1 um in diameter. The concentrations of PS nanoparticles, mixing ratios of polystyrene nanoparticle solutions and TiO2 pastes, and nanoparticle sizes are the fabrication parameters for study. The fabrication of DSCCs was started with a deposition of 100 nm compact TiO2 layer onto fluorine-doped tin oxide glass by e-beam evaporation. Then, porous TiO2 paste mixed with or without polystyrene nanoparticles was deposited on the compact TiO2 film using doctor-blade method. The sintering of porous TiO2 was taken place at 450 oC. During sintering, polystyrene balls evaporated, leaving abundant mount of cavities whose sizes depend on the mixing ratios of PS nanoparticle solutions and TiO2 pastes, as well as the polystyrene nanoparticle dimensions. Afterwards, the TiO2 electrodes were treated with TiCl4 solution, immersed in N719 dye solution, and assembled with Pt-coated FTO glass. At last, liquid electrolyte (E-Solar EL 100) was injected into the assembled cells. The current-voltage characteristics of solar cells were evaluated under AM1.5 simulated light using a Keithley 2000 electrometer. For DSSCs, made with 1 um diameter PS nanoparticle in TiO2 paste, the conversion efficiency reached 5.51% with short circuit current density of 12.2 mA/cm2. Compared to their counterparts made without the addition of PS nanoparticles in TiO2 pastes, the short circuit current and cell efficiency were both improved by 17%. The improvement of efficiency is positively correlated to the size of cavity created by polystyrene balls. Finally, we also used hollow microsphere TiO2 photoelectrode to make solid-state electrolyte dye-sensitized solar cells. The results were also discussed.