The effect of TiO2 nanoflowers as a compact layer for CdS quantum-dot sensitized solar cells with improved performance

Abstract

Currently, TiO₂ on a fluorine-doped tin oxide substrate is the most commonly used type of photoelectrode in high-efficiency quantum dot-sensitized solar cells (QDSSCs). The power conversion efficiency (PCE) of TiO₂ photoelectrodes is limited because of higher charge recombination and lower QD loading on the TiO₂ film. This article describes the effect of a TiO₂ compact layer on a TiO₂ film to enhance the performance of QDSSCs. TiO₂ nanoparticles were coated on an FTO substrate by the doctor-blade method and then the TiO₂ compact layer was successfully fabricated on the surface of the nanoparticles by a simple hydrothermal method. QDSSCs were made using these films as photoelectrodes with NiS counter electrodes. Under one sun illumination (AM 1.5 G, 100 mW cm⁻²), the QDSSCs showed PCEs of 2.19 and 2.93% for TCL1 and TCL2 based photoelectrodes, which are higher than the 1.33% value obtained with bare TiO₂. The compact-layer-coated film electrodes provide a lower charge-transfer resistance and higher light harvesting. The compact layer on the TiO₂ film is a more efficient photocatalyst than pure TiO₂ film and physically separates the injected electrons in the TiO₂ from the positively charged CdS QD/electrolyte.