Dye-sensitized solar cells based on graphene oxide and natural plant dye extract

Abstract

The world is advancing quickly in terms of population and technology and this has placed a high demand on energy. The exploitation of conventional sources of energy such as fossil fuel, has proven to be harmful to the environment and its biota. Consequently, there is a need to exploit clean, renewable and sustainable sources of energy like the sun. Dye-sensitized solar cells (DSSCs) have been of particular interest owing to their low price-to-performance ratio, relatively low cost of fabrication, availability of raw materials and eco-friendliness. The performance of the cell is highly dependent on the materials used for each of its components: the sensitizer, photoanode, counter electrode and the electrolyte. This work was carried out to study the photovoltaic properties of DSSCs based on TiO2-GO photoanodes sensitized with natural dye pigments. Graphene oxide (GO), synthesized from graphite by Hummer’s method, was incorporated into the photoanodes to study the effects of its varying composition on the photovoltaic performance of the cells. GO was incorporated into the photoanodes by forming a nanocomposite layer (GO-TiO2) onto a pristine TiO2 nanoparticle layer to form double-layer sensitized photoanodes. The synthesized GO was characterized by UV–vis spectroscopy showing an absorbance peak at 221 nm wavelength, characteristic of GO. Mimosa pudica dye, a chlorophyll dye, was extracted from the leaves of the photosensitive green plant to sensitize the photoanodes. The photovoltaic properties of the cells were evaluated by current density–voltage (JV) curves. Promising results were observed. Generally, the incorporation of GO in the double layer photoanodes enhanced the photovoltaic properties of the cells. This led to a 41% improvement in efficiency for 0.71 wt% GO double layer based DSSC compared to the single layer nanoparticle based DSSC. The highest efficiency was recorded for the double layer (DL) photoanode with 0.71 wt% GO composition (Voc = 0.284, Jsc = 16.085, FF = 0.00035, η = 0.1%). Furthermore, single-layer chlorophyll-sensitized photoanodes were compared with single-layer anthocyanin-sensitized photoanodes using Rhoeo spathacea and Hibiscus rosa-sinensis dye extracts. The highest efficiency was recorded for the TiO2/ Hibiscus rosa-sinensis (Voc = 0.468, Jsc = 0.039, FF = 0.485, η = 0.55%).