Abstract:
Dye-sensitized solar cells (DSCs) have emerged as a viable alternative to the conventional siliconbased
solar cells due to simple fabrication, low cost and tunable aesthetic features, such as colour and
transparency. The photoanode of DSCs, usually TiO2 layer, plays a crucial role in the overall power
conversion efficiency as it influences in both photon absorption and electron transport. The efficient
photoanode should have large surface area, well-connected internal pores and efficient light scattering
property. In order to further enhance the efficiencies of DSCs, different light scattering techniques are
used. Typically, this is achieved by employing another layer of TiO2 containing larger size spheres on top of
the smaller size particle layer of TiO2. In this work, we have succeeded in designing a hierarchically
structured TiO2 scattering layer consisting of sub-micron size TiO2 spheres composed of aggregates of TiO2
nanoparticles of size around 10 nm. The DSCs with hierarchical TiO2 sphere scattering layer sensitized with
N719 dye outperform the DSCs having TiO2 nanofiber and TiO2 nanotube scattering layers. The highest
current density of 14.80 mAcm-2 was achieved with TiO2 sphere scattering layer compared with TiO2
nanofiber and TiO2 nanotube scattering layers. The power conversion efficiency of DSC with hierarchical
TiO2 sphere scattering layer was 7.38 % under standard AM 1.5 illumination conditions, whereas the
efficiency of DSC without scattering layer was 6.68 % and the efficiency of DSC with TiO2 nanofiber
scattering layer and TiO2 nanotube scattering layer was 6.47 % and 7.03 % respectively. The diffuse
reflectance measurements reveals that the better performance of DSC with hierarchical TiO2 sphere
scattering layer is mainly due to the improved light harvesting by scattering of long wavelength radiation
by the sub-micron size TiO2 spheres.
