Interpreting impedance spectra of organic photovoltaic cells—Extracting charge transit and recombination rates

Journal Article · Sun Sep 28 00:00:00 EDT 2014 · Journal of Applied Physics

DOI:https://doi.org/10.1063/1.4896269· OSTI ID:22305731

Mullenbach, Tyler K.; Zou, Yunlong; Holst, James ^[1]

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1. New Products R and D, Sigma-Aldrich Corporation, 6000 N. Teutonia Avenue, Milwaukee, Wisconsin 53209 (United States)

Impedance spectroscopy has been widely used to extract the electron-hole recombination rate constant in organic photovoltaic cells (OPVs). This technique is typically performed on OPVs held at open-circuit. Under these conditions, the analysis is simplified with recombination as the only pathway for the decay of excess charge carriers; transit provides no net change in the charge density. In this work, we generalize the application and interpretation of impedance spectroscopy for bulk heterojunction OPVs at any operating voltage. This, in conjunction with reverse bias external quantum efficiency measurements, permits the extraction of both recombination and transit rate constants. Using this approach, the transit and recombination rate constants are determined for OPVs with a variety of electron donor-acceptor pairings and compositions. It is found that neither rate constant individually is sufficient to characterize the efficiency of charge collection in an OPV. It is demonstrated that a large recombination rate constant can be accompanied by a large transit rate constant, thus fast recombination is not necessarily detrimental to OPV performance. Extracting the transit and recombination rate constants permits a detailed understanding of how OPV architecture and processing conditions impact the transient behavior of charge carriers, elucidating the origin of optimum device configurations.

• OSTI ID: 22305731
• Journal Information: Journal of Applied Physics, Vol. 116, Issue 12; Other Information: (c) 2014 AIP Publishing LLC; Country of input: International Atomic Energy Agency (IAEA); ISSN 0021-8979
• Country of Publication: United States
• Language: English

Related Subjects

75 CONDENSED MATTER PHYSICS
SUPERCONDUCTIVITY AND SUPERFLUIDITY
BINDING ENERGY
CHARGE CARRIERS
CHARGE COLLECTION
CHARGE DENSITY
DECAY
ELECTRIC POTENTIAL
EQUIPMENT
EXTRACTION
HETEROJUNCTIONS
IMPEDANCE
PHOTOVOLTAIC CELLS
QUANTUM EFFICIENCY
REACTION KINETICS
RECOMBINATION
SPECTRA
SPECTROSCOPY
TRANSIENTS