ABSTRACT
A comparative assessment of nanowire versus nanoparticle-based ZnO dye-sensitized solar cells (DSSCs) is conducted to investigate the main parameters that affect device performance. Towards this aim, the influence of film morphology, dye adsorption, electron recombination and sensitizer pH on the power conversion efficiency (PCE) of the DSSCs is examined. Nanoparticle-based DSSCs with PCEs of up to 6.2% are developed and their main characteristics are examined. The efficiency of corresponding devices based on nanowire arrays (NW) is considerably lower (0.63%) by comparison, mainly due to low light harvesting ability of ZnO nanowire films. The dye loading of nanowire films is found to be approximately an order of magnitude lower than that of nanoparticle-based ones, regardless of their internal surface area. Inefficient anchoring of dye molecules on the semiconductor surface due to repelling electrostatic forces is identified as the main reason for this low dye loading. We propose a method of modifying the sensitizer solution by altering its pH, thereby enhancing dye adsorption. We report an increase in the PCE of nanowire DSSCs from 0.63% to 1.84% as a direct result of using such a modified dye solution.
ABSTRACT
The growth of MoS2 films by sulfurization of Mo foils at atmospheric pressure is reported. The growth procedure provides, in a controlled way, mono- and few-layer thick MoS2 films with substrate-scale uniformity across square-centimeter area on commercial foils without any pre- or post-treatment. The prepared few-layer MoS2 films are investigated as counter electrodes for dye-sensitized solar cells (DSSCs) by assessing their ability to catalyse the reduction of I3(-) to I(-) in triiodide redox shuttles. The dependence of the MoS2 catalytic activity on the number of monolayers is explored down to the bilayer thickness, showing performance similar to that of, and stability against corrosion better than, Pt-based nanostructured film. The DSSC with the MoS2-Mo counter electrode yields a photovoltaic energy conversion efficiency of 8.4%, very close to that of the Pt-FTO-based DSSC, i.e. 8.7%. The current results disclose a facile, cost-effective and green method for the fabrication of mechanically robust and chemically stable, few-layer MoS2 on flexible Mo substrates and further demonstrate that efficient counter electrodes for DSSCs can be prepared at thicknesses down to the 1-2 nm scale.
