Determination of charge-carrier mobility in disordered thin-film solar cells as a function of current density

Mäckel, Helmut; MacKenzie, Roderick C. I.

Abstract

Charge-carrier mobility is a fundamental material parameter, which plays an important role in determining solar-cell efficiency. The higher the mobility, the less time a charge carrier will spend in a device and the less likely it is that it will be lost to recombination. Despite the importance of this physical property, it is notoriously difficult to measure accurately in disordered thin-film solar cells under operating conditions. We, therefore, investigate a method previously proposed in the literature for the determination of mobility as a function of current density. The method is based on a simple analytical model that relates the mobility to carrier density and transport resistance. By revising the theoretical background of the method, we clearly demonstrate what type of mobility can be extracted (constant mobility or effective mobility of electrons and holes). We generalize the method to any combination of measurements that is able to determine the mean electron and hole carrier density, and the transport resistance at a given current density. We explore the robustness of the method by simulating typical organic solar-cell structures with a variety of physical properties, including unbalanced mobilities, unbalanced carrier densities, and for high or low carrier trapping rates. The simulations reveal that near VOC and JSC, the method fails due to the limitation of determining the transport resistance. However, away from these regions (and, importantly, around the maximum power point), the method can accurately determine charge-carrier mobility. In the presence of strong carrier trapping, the method overestimates the effective mobility due to an underestimation of the carrier density.

Citation

Mäckel, H., & MacKenzie, R. C. (2018). Determination of charge-carrier mobility in disordered thin-film solar cells as a function of current density. Physical Review Applied, 9(3), Article 034020. https://doi.org/10.1103/physrevapplied.9.034020

• Journal Article Type: Article
• Acceptance Date: Nov 21, 2017
• Online Publication Date: Mar 23, 2018
• Publication Date: Mar 23, 2018
• Deposit Date: Oct 29, 2018
• Publicly Available Date: Oct 29, 2018
• Journal: Physical Review Applied
• Publisher: American Physical Society
• Peer Reviewed: Peer Reviewed
• Volume: 9
• Issue: 3
• Article Number: 034020
• DOI: https://doi.org/10.1103/physrevapplied.9.034020
• Public URL: https://nottingham-repository.worktribe.com/output/1206239
• Publisher URL: https://journals.aps.org/prapplied/abstract/10.1103/PhysRevApplied.9.034020