Influence of Charge Carrier Mobility on the Performance of Organic Solar Cells

TL;DR

This study investigates how charge carrier mobility influences the efficiency of organic solar cells, finding an optimal mobility level that balances dissociation and recombination processes for maximum power conversion.

Contribution

First, it models the impact of charge mobility on organic solar cell efficiency considering injection barriers and reduced Langevin recombination, identifying an optimal mobility range.

Findings

Optimal mobility around 10^{-6} m^2/Vs improves efficiency by ~20%.

Mobility increase from 10^{-8} to 10^{-6} m^2/Vs yields maximum efficiency.

Recombination losses increase with higher mobility, affecting overall performance.

Abstract

The power conversion efficiency of organic solar cells based on donor--acceptor blends is governed by an interplay of polaron pair dissociation and bimolecular polaron recombination. Both processes are strongly dependent on the charge carrier mobility, the dissociation increasing with faster charge transport, with raised recombination losses at the same time. Using a macroscopic effective medium simulation, we calculate the optimum charge carrier mobility for the highest power conversion efficiency, for the first time accounting for injection barriers and a reduced Langevin-type recombination. An enhancement of the charge carrier mobility from $10^{-8}$m$^2$/Vs for state of the art polymer:fullerene solar cells to about $10^{-6}$m$^2$/Vs, which yields the maximum efficiency, corresponds to an improvement of only about 20% for the given parameter set.