Porphyrin molecules offer immense potential as the light harvesting component of dye-sensitised nanocrystalline TiO₂ solar cells. Synthetic porphyrin dyes were amongst the first dyes trialled for sensitisation of inorganic semiconducting oxides. Today, they exhibit the best performance reported for dye-sensitised solar cells. Accompanying the significant performance improvement over the last two decades is a much improved understanding of efficiency-determining fundamental electron transfer steps, from charge photogeneration to recombination. In this feature article we highlight our recent discoveries of the influence of porphyrin molecule structure on efficiency determining electron transfer kinetics and device performance by systematically changing the molecular structure and observing electron injection and recombination kinetics using time-resolved optical and electrical probes. Despite our observation of ultrafast charge injection for all porphyrin dyes studied by transient absorption spectroscopy, the injection yield estimated using an internal standard remains below 100% and depends strongly on the molecular structure. The observed discrepancy between kinetic competition and the injection yield is attributed to non-injecting dyes, probably arising due to inhomogeneity. A very interesting sub-ns (0.5 ns to 100 ns) charge recombination channel between photo-injected electrons and porphyrin cations is observed, which is found to be more prominent in free-base porphyrin dyes with a conjugated linker. Charge recombination between the acceptor species in the redox containing electrolyte and injected electrons is shown to be an important limitation of most porphyrin-sensitised solar cells, accelerated by the presence of porphyrin molecules at the TiO₂–electrolyte interface. This recombination reaction is strongly dependent on the porphyrin molecular structure. Bulky substituents, using a porphyrin dimer instead of a porphyrin monomer, a light soaking treatment of freshly prepared films and co-sensitization of TiO₂ with multiple dyes are shown to be successful strategies to improve electron lifetime. Finally, new developments unique to porphyrin dye-sensitised solar cells, including performance enhancements from a light exposure treatment of a zinc porphyrin dye, a significant performance improvement observed after co-sensitisation of TiO₂ with free-base and zinc porphyrin dyes and the use of porphyrin dimers with increased light harvesting in thin-film TiO₂ solar cells are described.

Asymmetric zinc phthalocyanines with alkyl chain substituents formed highly efficient light-harvesting layers on a TiO₂ surface. Dye-sensitized solar cells using PcS20 exhibited a record efficiency of 6.4% under one-sun irradiation.

The deployment of organic semiconducting materials for radiation detection is an emerging and highly attractive area of materials science research. These organic materials offer the enticing vision of technologies created from low-cost materials that can be printed on-demand with a range of different tailored optoelectronic functionalities. An explosion in the number of available materials, improved functionality of materials, and sophistication of solution-based device fabrication techniques for organic semiconductors in recent years have led to considerable opportunities for the utilization of organic materials in the detection of ionizing radiation. While the potential of organic semiconducting materials for low-cost radiation detection is clear, transitioning these printable materials to a commercial reality presents a significant scientific challenge. In this work, we provide a comprehensive analysis of the use of organic semiconductors for radiation detection. We discuss the fundamental physics of these materials and how their conduction mechanisms, including charge generation and charge transport, differ significantly from established inorganic semiconductors. Various strategies employed to control the nanostructure in organic semiconductors to optimize charge generation and transport for radiation detection are discussed. We provide insights into the strategies employed to fabricate organic semiconducting devices at industrially relevant scales using roll-to-roll solution processing and finally discuss existing examples of organic semiconducting materials utilized in the radiation detection arena.