Abstract
Submicron sized mesoporous spheres of TiO2 have been a potential alternative to overcome the light scattering limitations of TiO2 nanoparticles in dye-sensitized solar cells (DSSCs). Currently available methods for the growth of mesoporous TiO2 sub-microspheres involve long and relatively high temperature multi-stage protocols. In this work, TiO2 mesoporous sub-microspheres composed of ~5 nm anatase nanocrystallites were successfully synthesized using a rapid one-pot room-temperature CTAB-based solvothermal synthesis. X-Ray Diffraction (XRD) showed that the grown structures have pure anatase phase. Transmission electron microscopy (TEM) revealed that by reducing the surfactant/precursor concentration ratio, the morphology could be tuned from monodispersed nanoparticles into sub-micron sized mesoporous beads with controllable sizes (50–200 nm) and with good monodispersity as well. The growth mechanism is explained in terms of the competition between homogeneous nucleation/growth events versus surface energy induced agglomeration in a non-micelle CTAB-based soft templating environment. Further, dye-sensitized solar cells (DSSCs) were fabricated using the synthesized samples and characterized for their current-voltage characteristics. Interestingly, the DSSC prepared with 200 nm TiO2 sub-microspheres, with reduced surface area, has shown close efficiency (5.65%) to that of DSSC based on monodispersed 20 nm nanoparticles (5.79%). The results show that light scattering caused by the agglomerated sub-micron spheres could compensate for the larger surface areas provided by monodispersed nanoparticles.
Highlights
Dye-sensitized solar cells (DSSCs), since invented by O’Regan and Gratzel in 1991 [1], have been a promising low-cost photovoltaic technology [2,3,4,5,6,7]
In a typical dye-sensitized solar cells (DSSCs), solar energy photons are absorbed by compliantly absorbing dye molecules that are loaded on a mesoporous film of TiO2 nanoparticles
The dye-photogenerated electrons are subsequently injected into the TiO2 nanoparticles, through which they travel to the device photoanode
Summary
Dye-sensitized solar cells (DSSCs), since invented by O’Regan and Gratzel in 1991 [1], have been a promising low-cost photovoltaic technology [2,3,4,5,6,7]. In a typical DSSC, solar energy photons are absorbed by compliantly absorbing dye molecules that are loaded on a mesoporous film of TiO2 nanoparticles (typically ~20–30 nm). The dye-photogenerated electrons are subsequently injected into the TiO2 nanoparticles, through which they travel to the device photoanode. The TiO2 nanoparticles work, as an electron acceptor as well as an electron transport medium. The high surface area associated with the morphology of TiO2 nanoparticles plays a vital role in determining the amount of dye loading and the amount of generated electrons. The morphology of TiO2 nanoparticles determines the transport path which photoelectrons will subsequently take in their journey towards the external circuit through the thick layer of TiO2 nanoparticles [8,9,10]
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