Abstract

The electrical response of organic donor-acceptor heterojunction solar cells is not readily described by conventional semiconductor device models. In particular, the competition between charge collection and charge recombination is influenced by the disordered nature of charge transport and the heterogeneous microstructure of the active layer. In order to select and design materials with potential for higher performance, methods are needed to help understand first, how charge dynamics are related to the chemical and physical structure of the component materials and second, how the dispersive nature of the charge dynamics influences the current-voltage response of a photovoltaic device. We use a multi-scale modelling approach to simulate charge dynamics in organic electronic materials, incorporating molecular modelling of the microstructure of organic films, quantum chemical calculation of intermolecular charge transfer rates and kinetic Monte Carlo simulation of current transport and recombination. The methods are validated by a range of experimental measurements. Moreover, we have adapted continuum models of device behaviour to incorporate disorder in the electronic structure via a density-of-states function based on the microscopic studies. We will show how such an approach can be used to help explain the opto-electrical behaviour of organic photovoltaic materials and devices.