Chapter 9: Drift Diffusion Modelling of Charge Transport in Photovoltaic Devices

Much thin film photovoltaic (PV) device research is based on a ‘shake and bake’ approach, uninformed by an understanding of the underlying mechanisms. These devices consist of several layers of different materials so that the number of potential materials combinations is enormous. Atomistic models do not work on the length scales needed to study charge transport so device models are essential. The drift diffusion (DD) method is appropriate for charge transport in layered devices. This chapter describes the concepts underpinning DD simulations, provides a ‘how to’ guide for 1-dimensional DD simulation and shows how rescaling the variables leads to considerable insight into the physics of the problem. Finding an equivalent circuit for an organic PV device is given as an example. Since DD models of organic PV devices are reviewed in Chapter 13, our main example shows how a more sophisticated approach, employing a spectral method that predicts coupled ion–electron conduction in perovskite devices, allows us to understand the effect of mobile ions on the operational mechanism of the device.