Are Transport Models Able to Predict Charge Carrier Mobilities in Organic Semiconductors

Organic photovoltaic devices have been steadily becoming more efficient through a combination of reduction in voltage losses, minimization of recombination pathways, and an increase in dimensionality of charge carrier pathways. However, a transport description that predicts the carrier mobility based on the mechanisms behind charge generation and transport in organic semiconducting material blends has been challenging. The complexity is mainly due to the absence of long-range order and the weak band coupling between molecules. In this Feature Article, we discuss charge transport models through a tight-binding lattice model approach. From the introduction of lattice disorder, we make a correlated liquid metal analogy and describe the effects of disorder on transport with quantum mechanical diffusion, Anderson localization, and percolation. We show that it is possible to understand the high- and low-temperature mobility data, the factors which limit the mobility, and the nature of the effective mass of charge carriers.