A spatially smoothed device model for organic bulk heterojunction solar cells

The performance of organic bulk heterojunction (BHJ) solar cells depends strongly on the nanoscale morphology formed by the donor and acceptor materials. However, the majority of device models for organic BHJ solar cells are based on an effective-medium formulation that does not capture details of the underlying morphology. In order to link more detailed models with effective-medium models, we derive a spatially smoothed formulation for organic BHJ solar cells based on volume-averaging of a mathematical model that considers charge carrier transport, generation, and recombination in both the acceptor and donor phases. The formulation captures two essential morphological characteristics of the organic BHJ layer that are not found in existing effective-medium models: the effective interfacial area and the volume fraction ratio between donor and acceptor materials. In addition, effective charge carrier mobilities and diffusion coefficients are identified, which are determined for an “ideal” interpenetrated BHJ solar cell.