3D-Localisation - Three Dimensionally Defined Non-Fullerene Acceptors

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Sunlight presents an essentially infinite source of energy. Converting it into electricity, heat, or chemical energy is among the most appealing and effective approaches to tackling the energy crisis and reducing the impact of human activity induced climate change. Organic solar cells are one emerging technology that can aid in the transition to a renewable economy. They are lightweight, flexible devices which utilise readily available organic molecules and can be processed by energy-efficient, non-thermal methods unlike traditional silicon devices. The development of these devices has relied upon fullerenes as electron acceptor materials.Fullerenes are molecular forms of carbon with a spherical, soccer ball-like geometry which gives rise to delocalisation of electrons across the entire surface of the molecule. This structure attributes fullerene with a variety of unique properties, they can reversibly accept up to six electrons and can transport charges efficiently in three dimensions. However, it is now well-established that using fullerenes places strict limitations on organic solar cell performance. Fullerenes absorb sunlight only poorly and they participate in processes which are destructive to the device while under operation. Compounding this, they are expensive to produce and purchase, and are extremely challenging to chemically modify with any degree of control. This means that their optical and electronic properties cannot be easily tuned for solar cells or any other specific application. Ultimately, the use of fullerenes is non-sustainable therefore new non-fullerene acceptors are urgently required if these green energy technologies are to realise their full potential.This project takes a holistic view of the beneficial and detrimental properties of fullerenes and will use this approach to produce a completely new class of non-fullerene acceptors. These will serve to impact hugely on the delivery of renewable energy sources. There are two key facets to this approach:1) The use of three-dimensional molecular structures as a central scaffold. These will facilitate electronic delocalisation in three dimensions.2) By attaching selected heterocyclic side groups to these scaffolds, solar absorbance will be maximised, and the electrochemical and morphological properties of these new molecules will be controlled in a facile manner.This represents a step-change in the development of useful non-fullerene acceptors. A new generation of molecular materials for use in energy conversion technologies will be produced, and design rules for attaining truly fullerene-like behaviour in general, and for any application, will be established. In contrast with much of the existing work on organic electronic materials, which focusses upon molecules and polymers composed of planar heterocyclic fragments, exploring chemical space in three dimensions is key to the work proposed here. This adds significantly to the novelty of our approach.