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In this work, we investigated the morphology, electrical conductivity, catalytic properties, and binding energies of electronic states of a system consisting of acetylene carbon black (AB) and graphite as efficient and low-cost counter electrodes (CEs) for dye-sensitized solar cells (DSSCs), where ratios of AB to graphite of 0:1, 1:3, 1:1, 3:1, and 1:0 were investigated. These carbon-based CEs were characterized using four-point probe conductivity measurement, field emission scanning electron microscope (FE-SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), near-edge X-ray absorption fine structure (NAXAFS), electrochemical impedance spectrum (EIS), and current-voltage (I-V) performance. Introduction of small AB particles into graphite paste enhanced the electronic conductivity of AB-graphite composite due to the bridging of the graphite flakes for electrocatalytic activity of triiodide reduction. AB particles also offer large surface area to provide high electrochemical performance in DSSCs. The overall highest power conversion efficiency of 5.06% was achieved for the DSSC fabricated with a CE consisting of AB-graphite ratio of 3:1, which is comparable to the DSSC performance with conventional platinum (Pt) CE. These findings suggest that AB and graphite composite could be a promising CE for low-cost DSSCs.

Natural dye sensitizers from Ixora coccinea (anthocyanin) and Bougainvillea glabra (betalain) flowers were prepared in five different ratios of ethanol to water (0, 30, 50, 70, and 90 % ethanol), and the effect of dye aggregation toward dye sensitized solar cell (DSSC) performance was evaluated. As the concentration of ethanol increases, the tendency of dye molecules to aggregate increased in Ixora dye extracts while no definite trend was observed in Bougainvillea dye extracts. The best DSSC performances of Ixora and Bougainvillea dyes exhibited by extracts in 70 % ethanol and 0 % ethanol are 0.58 ± 0.02 and 0.25 ± 0.02 %, respectively. Both high conversion efficiencies were ascribed to high electron density and low charge transfer resistance. From this study, it was revealed that the performances of DSSC could be affected by the formulation of dye aggregation on the TiO2 surface.

We have tailored the extraction solvent of natural anthocyanin pigments from Ixora coccinea flower to lower charge transport resistance and enhance effective electron diffusion coefficient as well as absorption properties in DSSC sensitization. Six different extraction solvents were used in this study, namely, absolute ethanol, 70 % ethanol, acetone, dimethyl formamide, dimethyl sulfoxide, and distilled water. Dimethyl formamide was found to be able to extract the most anthocyanins from the Ixora flower, followed by dimethyl sulfoxide, acetone, absolute ethanol, 70 % ethanol, and distilled water, respectively. Dye-sensitized solar cells were fabricated using these extracted dyes as sensitizers and the cell performances were measured and characterized. The dye-sensitized solar cell equipped with a dye sensitizer extracted in 70 % ethanol achieved the highest conversion efficiency (ɳ = 0.50 ± 0.04 %) owing to its highest electron diffusion coefficient and lowest transport resistance in the TiO2/dye/electrolyte interface. This was followed by the cell equipped a with dye sensitizer extracted in acetone (ɳ = 0.30 ± 0.04 %), absolute ethanol (ɳ = 0.27 ± 0.01 %), dimethyl formamide (ɳ = 0.17 ± 0.01 %), dimethyl sulfoxide (ɳ = 0.16 ± 0.01 %), and distilled water (ɳ = 0.09 ± 0.003 %) in conversion efficiency performances, respectively. This study provides an insight into the importance of choosing the right medium for both dye extraction as well as the favorable solvent medium for dye adsorption onto TiO2.