Hydrothermal fabrication of hierarchically macroporous Zn2SnO4 for highly efficient dye-sensitized solar cells

Abstract

Hierarchical macroporous Zn₂SnO₄ consisting of nanoparticles has been synthesized for the first time through an in situ hydrothermal and a following annealing process in the presence of a polystyrene (PS) template. Zn₂SnO₄ macropore sizes are tuned in the range of 180–650 nm by selecting the appropriate size of PS spheres, and the building unit size of the Zn₂SnO₄ macropore is 4.2 nm regardless of the PS sizes. The photovoltaic performances of the dye-sensitized solar cell based on hierarchical macroporous Zn₂SnO₄ with 200, 400, 600 and 750 nm PS spheres are 5.01, 4.76, 4.39 and 3.92%, respectively. The smaller pore size of Zn₂SnO₄ exhibits higher photovoltaic performance, which is ascribed to the higher dye loading, faster electron transport rate and slower electron recombination rate. These are confirmed by UV-vis absorption spectroscopy, intensity-modulated photocurrent spectroscopy, intensity-modulated photovoltage spectroscopy and electrochemical impedance spectroscopy. The double layered photoelectrode based on a Zn₂SnO₄ nanoparticles dye adsorption layer (4.2 nm in particle size, 15 μm in film thickness) and a macroporous light scattering layer (180 nm in macropore size, 4.0 μm in thickness) shows a remarkable enhancement in power conversion efficiency (6.10%) compared to that of Zn₂SnO₄ nanoparticles photoelectrode (5.36%) because of its superior light scattering ability.