Abstract:
Quantum dot sensitized solar cells (QDSSCs) have gained increased attention due to the unique
properties of the semiconductor quantum dots (QDs), as light captivating materials. QDs facilitates
multiple exciton generation, tunable bandgaps, high absorption coefficient, and low power
consumption. Many studies have been carried out towards producing affordable QDSSCs with high
power conversion efficiencies, utilizing these properties. As a critical component of QDSSCs,
counter electrodes hold significant importance among these studies. Platinum (Pt), a widely used
counter electrode with QDSSCs, is being disfavored due to high cost, diminishing material supply,
and reduced catalytic activity, when used with polysulfide electrolyte which is the most common
electrolyte for QDSSCs, due to surface, adsorbed sulphur. Therefore, substantial investigations have
been carried out in searching for an alternative, affordable and effective counter electrode in these
devices. Among the suitable materials, tin oxide (SnO2), a wide bandgap semiconductor, has become
a promising candidate for counter electrode due to its high chemical stability, high electron mobility,
low cost and environmentally friendly nature. In this study, counter electrodes were fabricated by
depositing SnO2 films on fluorine-doped tin oxide (FTO) glass substrates by using a simple spray
pyrolysis technique. These counter electrodes were characterized by scanning electron microscopic
and Raman techniques. Photovoltaic properties of CdS quantum dots sensitized TiO2 solar cells with
polysulfide electrolyte were tested by using this novel counter electrode. QDSSCs fabricated with
optimized SnO2 counter electrode showed 1.47% power conversion efficiency under the illumination
of 100 mW cm-2, whereas the devices fabricated with conventional Pt coated counter electrodes
showed 1.08% under the same conditions. Therefore, about 36% enhancement in power conversion
efficiency could be obtained by employing this novel low-cost counter electrode in these QDSSCs.
Keywords: Counter electrode; SnO2; CdS; Quantum dot sensitized solar cell
