Impact of the intermixed phase and the channel network on the carrier mobility of nanostructured solar cells

Abstract

We analyzed the impact of the complex channel network of donor and acceptor domains in nanostructured solar cells on the mobility of the charge carriers moving by thermally activated hopping. Particular attention was given to the so called intermixed phase, or interface roughness, that has recently been shown to promote an increase in the cell efficiency. The domains were obtained from a Monte Carlo simulation of a two-species lattice gas. We generated domain morphologies with controllable channel size and interface roughness. The field and density dependence of the carrier hopping mobility in different morphologies was obtained by solving a master equation. Our results show that the mobility decreases with roughness and increases with typical channel sizes. The deleterious effect of the roughness on the mobility is quite dramatic at low carrier densities and high fields. The complex channel network is shown to be directly responsible for two potentially harmful effects to the cell performance: a remarkable decrease of the mobility with increasing field and the accumulation of charge at the domains interface, which leads to recombination losses.

Monte Carlo Simulation for Investigation of Morphology Dependent Charge Transport in Bulk-Heterojunction Organic Solar Cells

“…On the other hand, there are some reports on the simulation of charge transport in organic solar cells. For example, Koster and Woellner et al , have reported the investigation of the influence of morphology on the charge transport of BHJ solar cells by numerically solving the Pauli master equation. Heiber et al have investigated the effect of the tortuosity of the charge-transport pathways through a bulk heterojunction film on the charge transport using kinetic Monte Carlo simulations.…”