Hierarchical Tin Oxide Nanostructures for Dye-Sensitized Solar Cell Application

Nanoscale material manipulation is the key to increasing solar light harvesting and photon-to-electron conversion efficiency (PCE) for an organic–inorganic photovoltaic system. Many SnO₂ 1D nanostructures, including nanowires and nanobelts, have been employed because of their potential of enhancing the charge collection properties of DSSCs by eliminating losses caused by grain boundary scattering of carriers in nanoparticle-based DSSCs. Here, a new approach to growing hierarchical 1D SnO₂ nanostructured layer by catalyst-assisted pulsed laser deposition after introducing NiO into the SnO₂ target is reported, and a plausible growth mechanism to describe the observed hierarchical nanostructures is presented. A remarkable improvement in the solar cell performance, including open circuit voltage, short circuit current density, fill factor, and PCE, by simple surface modification of the hierarchical SnO₂ nanostructured photoanode is further demonstrated. Surface passivation is achieved on the as-deposited hierarchical SnO₂ nanostructures by dip coating with an MgO passivation layer of appropriately optimized thickness. Such an insulating layer is found to effectively reduce the recombination process caused by the higher electron mobility of SnO₂ photoanode nanostructures. Compared with a pristine SnO₂ nanobelt photoanode, a tenfold enhancement in their PCE (to 4.14%) has been observed for MgO-passivated hierarchical SnO₂ nanostructures.