Fabrication and Characterization of Dye-sensitized Solar Cells using Locally Sourced Natural Dyes and Synthetic Organic Dyes as Photosensitizers

Cooperating countries: Nigeria and Austria

Coordinating institution: Redeemer's University, Alexander Adesina Willoughby, willoughbya@run.edu.ng

Partner institutions: Johannes Kepler University

Project duration: 1 June 2023 - 31 May 2025

Budget: EUR 19.975

Abstract

The relatively low energy conversion efficiency of Dye-Sensitized Solar Cells (DSSCs) is a key challenge hindering the commercialization of the solar cell. The photochemical performance of the dye used as a photosensitizer for the DSSC greatly determines the efficiency of the solar cell. Besides, the dye absorbance, light scattering, and photoelectron injection in TiO2 semiconductor also contribute to the energy conversion efficiency of a DSSC. In this project, different locally sourced natural dyes in Nigeria will be investigated to determine those with high energy conversion efficiencies suitable for the fabrication of high-performance DSSCs. Synthesis of these dyes will be carried out to mimic the molecular moieties found in natural dyes observed to be the best candidates for photosensitizers in DSSCs. Additionally, Metal-Organic frameworks (MOFs) have the potential to improve the generation of photocurrent in DSSCs by utilizing the advantage of its highly ordered, functionally tuneable supramolecular properties. Therefore, MOFs would also be exploredas sensitizer in the fabrication of DSSCs towards enhancing the energy conversion efficiency of the solar cell. Success in this project would contribute greatly to the development of highly efficient DSSCs to produce clean, affordable, and sustainable energy which is in tandem with the United Nation SDGs #7 and #13.

Summary

Dyes are crucial photosensitizers in the functionality of dye-sensitized solar cells (DSSCs). DSSCs typically utilize synthetic dyes that are non-biodegradable and often toxic. However, substituting these synthetic dyes with inexpensive and biodegradable natural dyes can yield eco-friendly DSSCs. This study evaluates the efficacy of natural dye extracts from Vernonia amygdalina, Goeppertia macrosepala, and Cnestis ferruginea as photosensitizers in DSSCs. The impact of various solvents on the efficacy of these natural dye extracts was also assessed. Extraction of natural dyes was conducted with acetone and ethanol, followed by characterization via FTIR, UV–Vis, and photoluminescence spectroscopy. FTIR analysis confirmed the presence of hydroxyl, amine, and carbonyl groups, suggesting effective adsorption on semiconductor metal oxides in DSSCs. UV-Vis and PL data revealed that acetone and ethanol-extracted natural dyes exhibit robust optical absorption in the visible spectrum. Consequently, the assessed natural dyes represent viable photosensitizer candidates for DSSCs. The DSSC utilizing acetone-extracted V. amygdalina dye achieves superior solar conversion efficiency, with performance metrics of Jsc, Voc, FF, and η recorded at 330.51 µA/cm2, 522 mV, 0.7, and 0.12%, respectively. Chlorophyll-based dyes from V. amygdalina and G. macrosepala demonstrate higher solar efficiency than the anthocyaninbased dye from C. ferruginea. Acetone-extracted samples outperform those extracted with ethanol for V. amygdalina and G. macrosepala. The natural dyes exhibit lower electrical performance compared to synthetic ruthenium-based dyes (η = 2.84%) due to their inherent challenges, such as narrow absorption spectra, poor photostability, slow electron injection, and high recombination losses. 

The impact of co-sensitization on DSSC performance was also examined. DSSCs were fabricated using mixtures of Curcuma longa and Sorghum bicolor natural dye extracts in varying ratios: 1:1 (Mixed dye A), 1:2 (Mixed dye B), and 2:1 (Mixed dye C). The solar cells undergo characterization with a solar simulator and potentiostat. DSSCs sensitized with Mixed dyes A and C yield higher efficiency (η = 0.16%) compared to those with mixed dye B (η = 0.10%). Single dyes exhibit lower efficiency than the mixed dye configurations. Co-sensitization enhances the efficiency of Curcuma longa dye (η = 0.12%) by 30%, while that of Sorghum bicolor dye (η = 0.02%) is improved by 700% using the 1:1 and 2:1 mixing ratios. The EIS results indicate that Curcuma longa dye has superior recombination resistance compared to mixed dyes. The charge transfer resistances for Curcuma longa, Sorghum bicolor, Mixed dye A, Mixed dye B, and Mixed dye C were measured as 341, 155, 179, 196, and 296 Ω, respectively. Curcuma longa dye demonstrates higher efficiency than Sorghum bicolor attributed to an extended charge carrier lifetime. This prolonged lifetime suggests reduced recombination and improved electron collection efficiency.