Dye Sensitized Solar Cells

Substrate: The substrate in a DSSC provides structural support and serves as the foundation for other components. Common substrates include glass, plastic, or metal-coated glass. The choice of substrate influences the flexibility, transparency, and durability of the solar cell.

Transparent Conductive Oxide (TCO): TCO coatings, typically made of indium tin oxide (ITO) or fluorine-doped tin oxide (FTO), are applied onto the substrate to facilitate electron conduction while allowing light transmission. TCO layers enable efficient electron transport from the photoanode to the external circuit. Generally, FTO is preferred over ITO because FTO-coated substrates can withstand bending and deformation without compromising conductivity or optical transparency. FTO coatings tend to be more robust and durable than ITO coatings. Indium-based materials are susceptible to degradation over time, especially when exposed to harsh environmental conditions or mechanical stress.

Photoanode: The photoanode is a semiconductor material coated with a dye-sensitizing agent. Generally, Titanium dioxide (TiO2) is used as a semiconductor oxide due to its high surface area, stability, and suitable energy levels for charge separation. The dye molecules adsorbed onto the surface of TiO2 absorb photons and generate electron-hole pairs.TiO2 photoanodes can be prepared with different morphologies, including nanoparticles, nanowires, nanorods, nanotubes, and mesoporous films. Among these, mesoporous TiO2 films are popular due to their high surface area and interconnected pore structure. The surface of the TiO2 photoanode serves as the anchoring site for dye molecules, which absorb photons and generate electron-hole pairs through the process of photoexcitation. The choice of dye and the method of dye deposition onto the TiO2 surface influence the light absorption spectrum, charge injection efficiency, and overall photovoltaic performance of the DSSC.

Dye Sensitizer: Dye molecules play a vital role in the working DSSCs by absorbing light across a broad spectrum of wavelengths and injecting electrons into the semiconductor upon photo-excitation. Two types of dyes are known for DSSCs. Organic dyes (e.g., ruthenium-based complexes) and natural dyes (e.g., chlorophyll) are commonly employed as sensitizers. The choice of dye influences the absorption spectrum, charge injection efficiency, and overall performance of the solar cell.Ruthenium dyes are known for their excellent stability under persistent light exposure and harsh environmental conditions, which is the necessary condition for the long-term performance and reliability of DSSCs. The choice of ancillary ligands and further structural modifications can improve the stability, light-harvesting efficiency, and photovoltaic performance of ruthenium-based sensitizers.

Electrolyte: The electrolyte in DSSCs serves as a medium for charge transport between the photoanode and the counter electrode. Liquid electrolytes based on iodide/triiodide (I−/I3−) redox couples are widely used due to their high ionic conductivity and compatibility with various sensitizers. However, liquid electrolytes pose challenges related to leakage, evaporation, and stability, prompting research into solid-state and quasi-solid-state alternatives.

Counter Electrode: The counter electrode is typically coated with a catalyst (e.g., platinum) that facilitates the reduction of triiodide ions from the electrolyte, completing the electron circuit and enabling continuous operation of the solar cell.However, the high cost of Pt has prompted research into alternative materials that offer comparable performance at lower cost. Counter electrodes made of carbon-based materials or conductive polymers have also been investigated as cost-effective alternatives.Generally,carbon black, carbon nanotubes, graphene, and graphite have been extensively investigated as cost-effective alternatives to Pt for counter electrode applications in DSSCs. These materials exhibit good electrical conductivity, high surface area, and inherent catalytic activity towards the reduction of triiodide ions, making them promising candidates for sustainable and scalable DSSC technology.Counter electrodes can be fabricated using various techniques, including screen printing, doctor-blade coating, spin coating, and electrode position. The choice of fabrication method depends on factors such as substrate type, desired morphology, and scalability. Optimizing the fabrication process is crucial for achieving uniform and well-defined counter electrode structures with high catalytic activity and stability.

Sealing Material: Sealing materials are essential for encapsulating the components of DSSCs and protecting them from environmental factors such as moisture, oxygen, and UV radiation. Proper sealing enhances the long-term stability and reliability of solar cells. Generally, we use a polymer gasket with cover glass to seal the device properly.Commonly used polymer materials include epoxy resins, silicone elastomers, polyurethanes, and fluoro-polymers. These materials offer flexibility, ease of processing, and good adhesion to the substrate, making them suitable for encapsulating complex DSSC geometries.