Effect of using betalain, anthocyanin and chlorophyll dyes together as a sensitizer on enhancing the efficiency of dye‐sensitized solar cell

Abstract

The paper explored the mechanism of working of dye sensitizers for the improvement of efficiency of environmentally benign dye-sensitized solar cells (DSSC). The identified natural dyes namely anthocyanin (A), betalain (B) and chlorophyll (C) were extracted from Roselle (Hibiscus sabdariffa L.), spinach (Spinacia oleracea) and beetroot (Beta vulgaris) respectively. Light absorption performance of dyes was recorded by ultraviolet-visible (UV-vis) spectroscopic analysis followed by direct and indirect band gap calculation. The effect of functional groups present in the dyes studied by Fourier transform infrared spectroscopy (FTIR) and binding of the dyes on TiO 2 through surface morphology of sheets was identified employing field emission scanning electron microscopy (FESEM). Photovoltage characteristics (I-V) and induced photon to current efficiency (IPCE) measurements were also noted followed by the stability studies. The N3 (synthetic dye chosen for the reference) dye-based cell showed the highest efficiency of 6.19% out of all of 11 cells fabricated using different sensitizers. The DSSC fabricated using the novel mixed dye (ABC) mixture gave the highest efficiency of 3.73%, however it showed similar drop (almost 22%) in efficiency as that with of N3 dye in stability studies. The mechanism for the increase in the overall power conversion efficiency of DSSC was also suggested.

Enhancing the Conversion Efficiency of Dye-Sensitized Solar Cells based on Betalain Natural Dye as The Potential Photosensitizer: A Review

“…The efficiency of betalain-chlorophyll was better than efficiency of DSSCs device using mono-sensitization of betalain i.e., 0.674%. The other result of betalain-chlorophyll cosensitization was also reported by Patni's group research [31]. the combined dye elevated the efficiency of cell device compared to using betalain (η of 1.29%) and chlorophyll (η of 0.95 %) individually.…”

“…Once more, this result also showed that higher betaxanthin composition gave significant result in device efficiency and to achieve higher efficiency of device based on betalain dye, the favorable composition is importantly needed. Furthermore, the absorption spectra of betalain dye-TiO2 film (both betaxanthin and betanin) were also reported to have red-shift absorption compare to the absorption of dye in solution state [16,28,31]. This red-shift implied the existence of strong electronic coupling between betalain dye and TiO2 film [16], carrying the possibility to achieve higher DSSCs device efficiency in comparison with other natural dyes.…”

“…The carboxyl group in betalain dye has been reported to have good anchor with TiO2 compared to hydroxyl group in anthocyanin [28]. This become the reason why betalain dye has higher efficiency than dye-sensitized solar cell based on anthocyanin as has been informed in previous natural sensitizer reports [28][29][30][31]. The reported conversion efficiency of DSSCs device based on betalain dyes are summarized in Table 1 below.…”

“…This combination term is actually similar with mixing definition. The main consideration supporting this method is combining the different dyes could increase the number of binding sites between natural dye and semiconductor [31]. If the number of binding sites rises, then it would lead to strong interaction with semiconductor and result in the increasing of electron injected.…”

“…On the other side, betalain dye can support chlorophyll limitation in binding with ZnO surface because of having carboxyl groups. In chlorophyl dye, the dye would form a binding interaction with semiconductor surface through carbonyl (C=O) and -O ligands [30,31,40,43]. These two ligands tended to form poor binding site with photoanode (in this case is ZnO) surface because they would compete to get fixed to the ZnO surface.…”