Two natural dyes extracted from gardenia yellow (Gardenia jasminoides) and cochineal (Dactylopius coccus)
were used as sensitizers in the assembly of dye-sensitized solar cells (DSSCs) to harvest light over a
wide range of wavelengths. The adsorption characteristics, electrochemical properties and photovoltaic
efficiencies of the natural DSSCs were investigated. The adsorption kinetics data of the dyes were
obtained in a small adsorption chamber and fitted with a pseudo-second-order model. The photovoltaic
performance of a photo-electrode adsorbed with single-dye (gardenia or cochineal) or the mixture or successive
adsorption of the two dyes, was evaluated from current–voltage measurements. The energy conversion
efficiency of the TiO2 electrode with the successive adsorption of cochineal and gardenia dyes was
0.48%, which was enhanced compared to single-dye adsorption. Overall, a double layer of the two natural
dyes as sensitizers was successfully formulated on the nanoporous TiO2 surface based on the differences
in their adsorption affinities of gardenia and cochineal.