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Proceedings Paper

Nonequilibrium and equilibrium operation of organic disordered semiconductor devices (Conference Presentation)

Paper Abstract

Organic semiconducting materials are typically subject to energetic and positional disorder and localization of electronic states. The electronic behavior of these materials are therefore strongly influenced by thermalization of charge carriers in the localized density of states (DOS). Consequently, non-equilibrium processes play an important role in the operation of devices made of such materials. We show as an example that measurements of recombination dynamics, conducted under transient or steady-state conditions, can easily be misinterpreted when a detailed understanding of the interplay of thermalization and recombination is missing. To enable adequate measurement analysis, we solve the multiple-trapping problem for recombining charge carriers and analyze it in the transient and steady excitation paradigm for different DOS distributions. We show that recombination rates measured after pulsed excitation are inherently time-dependent, since recombination gradually slows down as carriers relax in the DOS. When measuring the recombination order after pulsed excitation, this leads to an apparent high-order recombination at short times. As times goes on, the recombination order approaches an asymptotic value. For the Gaussian and the exponential DOS distributions, this asymptotic value equals the recombination order under continuous excitation. For a more general DOS distribution, the recombination order can also depend on the carrier density, under both transient and steady-state conditions. However, we show that there are cases where thermal equilibrium is never attained in the device. We conclude that transient experiments can provide rich information about recombination in and out of equilibrium and the underlying DOS occupation provided that consistent modeling of the system is performed.

Paper Details

Date Published: 23 May 2018
Proc. SPIE 10687, Organic Electronics and Photonics: Fundamentals and Devices, 106870G (23 May 2018); doi: 10.1117/12.2307655
Show Author Affiliations
Andreas Hofacker, TU Dresden (Germany)
Dieter Neher, Univ. Potsdam (Germany)
Karl Leo, TU Dresden (Germany)

Published in SPIE Proceedings Vol. 10687:
Organic Electronics and Photonics: Fundamentals and Devices
Sebastian Reineke; Koen Vandewal, Editor(s)

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