María Fernanda Cerdá

Calendula officinalis extract was evaluated as a functionalization agent for gold nanoparticles (AuNPs). The resulting nanoconjugate (AuNP-Cale) was thoroughly characterized, and explored as a sensitizer for dye-sensitized solar cells (DSSC). As a starting point, citrate-reduced AuNPs (AuNP-Cit) were synthesized and fully characterized. Comprehensive characterization for both AuNP-Cit and AuNP-Cale included dynamic light scattering (DLS), electrophoretic light scattering (ELS), colloidal and stability assay. Successful functionalization included increased hydrodynamic diameter, reduced zeta potential, and improved colloidal stability. DSSC evaluation demonstrated that while pre-formed AuNP-Cale did not enhance efficiency, improved performance was achieved when AuNP-Cit was added sequentially after the extract on the TiO2 electrode, likely due to better electrode coverage. This result correlated with enhanced light absorption (FORS) and favorable EIS parameters.

Dye-sensitized solar cells comprise a fluorine doped tin oxide/titanium dioxide photoanode and a counter electrode of fluorine doped tin oxide covered with a catalytic material arranged in a sandwich configuration. Many processes take place inside a dye-sensitized solar cell. However, two involve the redox couple contained in the electrolyte solution: the dye regeneration and the recombination. While the first is a desired path, the latter impacts the power conversion efficiency of the cells, decreasing the measured values. In this work, iodine-based couples are evaluated using cyclic voltammetric measurements, and their behaviour is compared with two commercial electrolytes widely used in dye-sensitized solar cells, particularly when sensitized with natural dyes. Different experimental conditions, such as cell configurations and electrode materials, were adopted to understand the thermodynamics of the competitive electron transfer processes mentioned above.

Three filamentous freshwater cyanobacterial strains were grown at high light intensity to produce lipidic dyes composed of xanthophylls, carotenes, and chlorophyll a. The properties of the pigments were evaluated as suitable natural compounds to be applied in dye-sensitized solar cells (DSSC). The assembled DSSC were characterized using the density current vs. potential profiles and electrochemical impedance spectroscopy. With an efficiency of 0.127%, our results are higher than those previously reported using similarly structured compounds from natural sources such as algae and cyanobacteria, among others. The best efficiencies were probably related to myxoxanthophyll-like derivates and aphanizophyll are carotenoids with many hydroxyl groups being able to interact with the semiconductor surface. The stability of the bonding between the dyes and the titanium oxide of the photoelectrode is crucial to ensuring the acceptable performance of the DSSC, which was successfully achieved in our experiments with carotenoids with many hydroxyl groups. Our results point to cyanobacterial pigments as a promising source of natural dyes for use in solar cells.

Three filamentous freshwater cyanobacterial strains were grown at high light intensity to produce lipidic dyes composed of xanthophylls, carotenes and chlorophyll a. The properties of the pigments were evaluated as suitable natural compounds to be applied in dye-sensitized solar cells (DSSC). The assembled DSSC were characterized using the density current vs. potential profiles and electrochemical impedance spectroscopy. With an efficiency of 0.127 %, our results are higher than those previously reported using similar structured compounds from natural sources as algae and cyanobacteria, among others. The best efficiencies were probably related to the strains with high content in pigments probably related to myxoxanthophyll-like derivates and aphanizophyll, carotenoids with many hydroxyl groups able to interact with the semiconductor surface. The stability of the bonding between the dyes and the titanium oxide of the photoelectrode is crucial to ensuring acceptable performance of the DSSC, which was successfully achieved in our experiments with carotenoids with many hydroxyl groups. Our results point to cyanobacterial pigments as a promising source of natural dyes for use in solar cells.

This work aimed to show the possibility of applying anthocyanins extracted from blueberries following a straightforward path as potential impregnation dyes in dye-sensitized solar cells (DSSCs), particularly in the presence of co-adsorbents, such as silver nanoparticles, as an alternative in order to profit from large amounts of discarded fruits. Following a simple procedure, anthocyanins (mainly delphinidin-3-glucoside) were obtained from blueberries (Southern Highbush type). Complete characterization was carried out in order to prove the utility of delphinidin-3-glucoside as a sensitizer in DSSCs. The analyzed anthocyanin is suitable for sensitizing because of its high molar absorptivity values within the visible region of the light spectra, the adsorption ability to a FTO/TiO₂ electrode (FTO, fluorine-doped tin oxide) as confirmed by Fourier transform infrared (FTIR) as well as thermogravimetry coupled to differential scanning calorimetry (TG-DSC), a potential oxidation value near 1 V, and adequate thermal as well as light stabilities. Moreover, the cell’s conversion efficiency is improved in the presence of silver nanoparticles, reaching 0.24% (nearly a 25% increase). The sum of all these characteristics points to the application of delphinidin-3-glucoside as a sensitizer in DSSCs, offering a technological use with potential interest for countries where agricultural production offers an abundant origin of extraction.

DSSC technology based on natural dyes still constitutes a tempting alternative to explore. Besides the ease of extraction, most natural dyes fulfill the characteristics to be applied as sensitizers. The presented results summarize the exploration of the features of several southern dyes, mostly coming from the Antarctic region. The explored pigments showed good absorption capacity within the visible region of the light spectra, and their molecules possess functional moieties to coordinate with the TiO₂ semiconductor, oxidation potential value near 1 V and reduction potential near −0.8 V, adequate thermal stability, and low fluorescence emission.

The construction of a small-sized panel based on anthocyanins from Erythrina crista-galli as sensitizers is reported in this work. The device, named KD12, was placed indoors at the Artigas Antarctic Scientific Base from March 2019 to December 2020. Here is released for the first time, the indoor installation of dye-sensitized solar cells based on pigments from the Uruguayan national flower at an Antarctic Base and the evaluation of their performance during nineteen months. The panel showed good stability and maintained its efficiency conversion performance over the period. The output power, voltage and conversion efficiency generated for this device mainly depended on irradiance and external factors as light reflection due to snow or artificial bulbs near the area. Additional protection was provided by the double-glass window in front of the panel, lowering lighting irradiance and changing spectral characteristics of the light incident the device. A new prospect raised here: the potential application of anthocyanins as sensitizers for indoor electricity generation in the Antarctic area with long term operability, where low temperatures are helpful considering the thermal stability of the dyes. These constitute an interesting first step of a low-cost alternative searching for clean energy generation sources, focusing on a cold region like Antarctica.