Synthesis and Development of New Dyes and Electron Transport Mediators for p-Type Dye Sensitized Solar Cell Applications

Abstract

NiO-based p-type dye-sensitized solar cells (p-DSSCs) have garnered significant attention, as they are often the limiting factor in achieving high-efficiency tandem DSSCs. In these cells, the dye plays a critical role in light absorption and photocurrent generation, making the design of new sensitisers essential for enhanced device performance. Due to the relatively thin NiO films used (around 1.5 µm), organic dyes with high extinction coefficients are needed to optimise light absorption. In tandem DSSCs, NiO-based p-DSSCs are combined with TiO2 as n-type DSSCs, requiring complementary light absorption across different wavelength ranges. Since n-type devices are optimised for capturing higher-energy photons, dyes for NiO-based cells must efficiently absorb light in the longer-wavelength visible and near-IR regions. Additionally, an anchoring unit, such as a carboxylic acid group, is crucial for dye attachment to the semiconductor surface, facilitating effective charge transfer from NiO to the dye. In a solid-state DSSC (ssDSSC), the cell was constructed on FTO glass with a NiO layer and a benchmark dye, infiltrated with PCBM, and capped with an aluminum contact. However, limited photocurrent was observed, likely due to the PCBM layer, suggesting that alternative electron transport materials may be required to further enhance performance. In this thesis, electron transport materials (ETM), N-heterocyclic dyes, aza-BODIPY catechol dyes, and novel BODIPY dyes were synthesised and studied as sensitisers for p-DSSCs. Each chapter addresses a specific aspect of dye design, offering a comprehensive analysis of the factors critical to developing an efficient device.