The work to date has provided computationally efficient tools to model the structure and electronic properties of molecular electronic materials, to design new materials and to understand the behaviour of such materials when applied to solar energy conversion and charge storage. In the case of polymer photocatalysts, we combined different modelling tools to show that the interactions between the polymer and its liquid environment control the likelihood of the first step in the photocatalytic process (Figure 1). We used the understanding to design better performing materials. Previous approaches had not considered the polymer-solvent interactions. In a separate study we developed a new model of charge recombination at a molecular interface, something which is relevant to both photovoltaic and photochemical solar energy conversion. We discovered that the non-radiative recombination, the main loss pathway in molecular materials, is controlled partly by the brightness of the excited states at the interface, and that this can in turn be controlled by choosing the energy levels of the materials. This represents a design rule to bring molecular solar energy energy conversion closer to the ideal limit. Finally, we demonstrated a novel battery device using conjugated polymers with polar side chain that can transport and store ions (Figure 2). The device could charge and discharge very rapidly compared to state-of-the art lithium ion devices and operates in a safe, salt-water electrolyte.
Figure 1. Snapshots of molecular dynamics simulation showing that whilst a polar polymer (b) photocatalyst avoids water, a non-polar polymer (a) locates at the interface between water and the sacrificial electron donor, triarylamine. In the latter case, the presence of the water increases the driving energy for charge separation, which is the first stage of the photocatalytic process.
Figure 2. (a) schematic of the battery device based on conjugated polymer electrodes with a salt-water electrolyte. (b) reactions that occur at the anode and cathode under changing and discharging.