2.2. Morphological investigation on TiO2

For LSPR based enhancement of DSCs the size of the metal nanoparticles plays huge role. Such as at 5 nm regime of metal nanostructure non-radiative processes are dominant, near field coupling for 45 nm size regime and far field scattering for 120 nm size metal nanostructures [62]. In terms of application, some reports evidence the beneficial effect of topical presence of plasmonic nanoparticles on TiO2 film, however, homogenous integration of plasmonic nanoparticles throughout active layer have proven more efficient, particularly in enhancing photocurrent

Figure 5. Summary of radiative (a) and (b) and non-radiative LSPR-based processes and their features, modified from

The highest PCE achieved through plasmonic enhancements so far (2013) is 10.8% which is 30% higher (8.3% PCE) than the control device employing N719 sensitizer by Belcher et al.. with 0.01–0.32% core shell particles mixed with regular TiO2 [61]. In this study, oxide-metaloxide multiple core-shell nanostructured spheres were blended with already available photoactive materials to achieve balanced light harvesting in panchromatic fashion. Kamat et al.. in a pioneering work (2012) identified the plasmonic and charging effect based on the composition of Au@SiO2 and Au@TiO2, leading to achieve a higher photocurrent and photovoltage with overall PCE of 10.2 and 9.7%, respectively [60]. Au nanoparticles of 5 nm size were used in the core with shell as passivation layer of either SiO2 or TiO2 and mixed with Solaronix T/SP paste in 0.7 wt%. Wang et al in 2013, in a unique study employed the organic

10.1% PCE improved from 5.5% PCE (84% increase) [66]. Au nano colloid in 0–0.8 wt% ratio

, along with TiO2 inlaid 2 nm sized Au nanoparticles resulting in

response of devices (Figure 6) [67, 68].

reference [62], with permission from the Royal Society of Chemistry.

394 Titanium Dioxide - Material for a Sustainable Environment

sensitizer FNE29 and I/I3

NP based mesoporous TiO2 shows excellent features for DSCs however it suffers from low electrical conductivity and charge recombination losses [75–78]. Additionally, enhanced light scattering and dye adsorption can be achieved by modifying the shape of NPs or mixing nanotubes, nanowires, nanospheres, and hollow TiO2 [58, 77–81]. On the same note, 2D and 3D structures of TiO2 such as nanoribbons, nanodisks, nanoleaves, nanoflowers, nanorods, hedgehog nanostructure and dendritic hollow structures have also be explored for DSCs [82–87]. The studies focused on the morphological modification of TiO2 have demonstrated marginal increase in DSC performance with scattered results, however, due to structural complexity and reproducibility issues such investigations has not resulted in wide spread application for DSCs [76]. For details please refer to the cited work.
