Characterization of asymmetric electron and hole transport in a high-mobility semiconducting polymer

The electron and hole transport properties in a high-mobility n-type copolymer poly{[N,N′-bis(2-octyldodecyl)-naphthalene-1,4,5,8-bis(dicarboximide)-2,6-diy1]-alt-5,5′-(2,2′-dithiophene)}[P(NDI2OD-T2), PolyeraActivInk™ N2200] are investigated. The electron mobility is observed to be more than two orders of magnitude higher than the hole mobility. The thickness-dependent current density versus voltage (J–V) characteristics of N2200 electron-only and hole-only devices cannot be well described using the conventional mobility model. However, the thickness-dependent and temperature-dependent J–V characteristics of N2200 electron-only and hole-only devices can be accurately described using our recently introduced improved mobility model only with a single set of parameters. Within the improved model, the mobility depends on three important physical quantities: the temperature, carrier density, and electric field. For the semiconducting polymer studied, we find the width of the Gaussian density of states σ = 0.082 eV and the lattice constant a = 0.8 nm for electron transport, while the width of the Gaussian density of states σ = 0.11 eV and the lattice constant a = 0.8 nm for hole transport. It is clear that hole transport exhibits a significantly stronger disorder than electron transport. This is also reflected in the lower hole mobility, as compared to the electron mobility.