Jenny Nelson1

1, Imperial College London, London, , United Kingdom

In a molecular photovoltaic device, charge separation and energy conversion result from the evolution of a photogenerated exciton into a charge separated state, in competition with recombination to ground. The efficiency of charge separation is a function of the molecular packing and energy level alignment near the interface, and of disorder in these properties. Understanding the effect of structure, energetics and disorder on the competition between charge separation and recombination help to identify the factors controlling device photovoltage and ultimately conversion efficiency. Here, we address the factors controlling photovoltage in molecular donor: acceptor solar cells using a combination of electrical and spectroscopic measurements and numerical models. We explore the limits to Voc using a model of non-radiative recombination, building on prior work [1], and demonstrate how choice of materials and control of processing may influence voltage losses. We use these results to consider the relative importance of interface and bulk regions of the materials and the ultimate limitations placed on solar to electric conversion by the molecular nature of the materials. In a second application example we address the role of chemical structure, molecular organisation and environment on the efficiency of charge separation, and subsequent photocatalytic activity, in conjugated polymer photocatalysts. We consider the relevance of models of charge separation in organic solar cells to photocatalysis.
[1] J. Benduhn et al. Nat. Energy (2017) DOI: 10.1038/nenergy.2017.53