Investigation of the use of synthetic and natural dyes in solar cells

Humanity's constant and growing need for energy has led to a search for sustainable and environmentally friendly energy sources. With the emergence of new needs due to advancing technology, scientific research on clean energy production has increased. Renewable energy sources are obtained from naturally available resources that can be harnessed continuously and consistently. Renewable energies such as wind, solar, biomass, geothermal, wave energy, and hydroelectric power offer sustainable alternatives compared to fossil fuels like oil, coal, and natural gas, as they are inexhaustible and produce low levels of CO2 emissions. The production of electricity from solar energy has become a significant area of research led by universities and scientists. In recent years, with the rising environmental awareness and public pressure to reduce reliance on fossil fuels, international companies have also shifted their investments toward renewable energy sources. Thanks to large corporations' investments in solar energy, technological advancements have accelerated, production capacity has increased, and mass production has led to a rapid decrease in costs. Consequently, solar energy technologies, which were previously considered expensive compared to traditional electricity generation methods, have now become more accessible and capable of contributing to power generation. Dye-sensitized solar cells (DSSCs) have emerged as a promising technology for renewable energy generation due to their low cost, ease of manufacturing, and potential for large-scale applications. However, achieving higher power conversion efficiency (PCE) remains a challenge. In this study, the researchers aim to enhance the performance of DSSCs by using both natural dyes, anthocyanin (extracted from butterfly pea flowers) and chlorophyll (extracted from spinach leaves), alongside synthetic metal-free dyes (BIM33 and C1). The study also introduces novel amine-based co-adsorbents, triethylamine (TEA) and diethylenetriamine (DETA), to suppress dye aggregation, which is a common issue in DSSCs and can limit their efficiency. The natural dyes used in this study were extracted through ultrasound-assisted extraction (UAE), a method proven to enhance dye extraction efficiency. Anthocyanin (ANT) was extracted from blue butterfly pea flowers and chlorophyll (CHL) from spinach leaves. Additionally, two synthetic metal-free dyes, BIM33 and C1, were utilized. Two co-sensitization techniques were employed. Cocktail co-sensitization: A mixture of dyes is applied to the TiO2 substrate simultaneously. Stepwise co-sensitization: The dyes are applied sequentially, allowing for more controlled layering of the sensitizers on the surface. To prevent dye aggregation, TEA and DETA were used as alternative co-adsorbents to CDCA (commonly used). These co-adsorbents were tested in various concentrations to determine their optimal effect on dye aggregation and electron injection. The optical properties of the dyes were evaluated using UV-Vis spectroscopy to determine their light absorption range, both in solution and when adsorbed on TiO2. Cyclic voltammetry (CV) was employed to measure the electrochemical properties of the dyes, including the energy levels of their highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO). The photovoltaic properties of the DSSCs were measured using current density-voltage (J-V) characteristics, and electron transport properties were studied using electrochemical impedance spectroscopy (EIS). The UV-Vis absorption spectra of anthocyanin and chlorophyll demonstrated a broad absorption range, particularly when the dyes were co-sensitized. This co-sensitization allowed for better coverage of the solar spectrum, particularly in the visible range, which is critical for improving the photovoltaic efficiency of DSSCs. The absorption properties of anthocyanin were further improved with the addition of co-adsorbents like TEA and DETA, which shifted the absorption peak and enhanced light harvesting. The PCE of DSSCs based on anthocyanin alone was 1.95%, but this efficiency increased to 2.42% when 0.01 mM CDCA was added as a co-adsorbent. Further, by using TEA and DETA as alternative co-adsorbents, the PCE improved to 3.11% and 4.33%, respectively. The best results were achieved with DETA, which not only prevented dye aggregation but also improved the electron injection efficiency by forming a more compact dye layer on the TiO2 surface. Chlorophyll alone exhibited a lower PCE of 1.19%, which was less efficient compared to anthocyanin. However, when combined with anthocyanin in a cocktail co-sensitization approach, the PCE increased to 2.39%, demonstrating the effectiveness of co-sensitization in improving light harvesting. For DSSCs based on the synthetic dyes BIM33 and C1, co-adsorbents also played a significant role in improving efficiency. When TEA was used as a co-adsorbent, the PCE of BIM33 increased from 3.19% to 4.60%, and C1 increased from 5.01% to 6.31%. This highlights the importance of selecting the appropriate co-adsorbent based on the molecular structure of the dye. The stepwise co-sensitization of anthocyanin with BIM33 and C1 also led to efficiency improvements, with PCEs of 4.28% and 6.25%, respectively. Although the performance was slightly lower than using TEA as a co-adsorbent, the stepwise approach demonstrated the potential of combining natural and synthetic dyes to optimize solar cell performance. Optical and electrochemical characterisations of the dyes showed that the HOMO and LUMO energy levels are suitable for electron injection into the conduction band of TiO2 and regeneration by the redox electrolyte. This enabled efficient charge transfer in BDGHs. With the use of IPCE analyses, TEA and DETA, the efficiency of all processes in the cell from photon absorption to electron transport was evaluated and the JSC graph was combined and the overall performance of the cell was analysed in detail. EIS analyses were performed to understand the electro-chemical and interfacial processes affecting cell performance in solar cells. The charge recombination resistance obtained from Nyquist diagrams and the electron lifetime estimated from bode diagrams are in agreement with the variations in experimental VOC values. This study provides valuable insights into improving the efficiency of DSSCs through the use of co-sensitization and co-adsorption strategies. By combining natural dyes (anthocyanin and chlorophyll) with synthetic dyes (BIM33 and C1), and introducing alternative co-adsorbents (TEA and DETA), the researchers successfully enhanced the light-harvesting capabilities and electron injection efficiency of the solar cells. The highest PCE achieved was 6.31% with the synthetic dye C1 and TEA as a co-adsorbent, while the best performance for natural dyes was 4.33% with anthocyanin and DETA. These findings demonstrate that sustainable, environment-friendly DSSCs can be optimized for higher efficiency through careful selection of dyes and co-adsorbents, offering a promising pathway toward more affordable and efficient solar energy technologies.