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Monte Carlo simulation of geminate pair recombination dynamics in organic photovoltaic devices : multi-exponential, field-dependent kinetics and its interpretation.

Jones, L.M. and Chakrabarti, B. and Groves, C. (2014) 'Monte Carlo simulation of geminate pair recombination dynamics in organic photovoltaic devices : multi-exponential, field-dependent kinetics and its interpretation.', Journal of physical chemistry C., 118 (1). pp. 85-91.

Abstract

Monte Carlo simulations are used to examine charge-transfer (CT) state recombination dynamics considering the effects of energetic disorder and bulk heterojunction morphology. Strongly biexponential recombination kinetics were observed, in agreement with spectroscopy. Data over a range of electric fields 106 ≤ F ≤ 108 V m–1 suggest that the slow component of recombination is due to energetic and spatial trapping of charges, as increasing the field reduces the magnitude of the slow decay. This behavior could not be described using a simple Onsager–Braun type model; hence, an alternative kinetic framework including an intermediate “quasi-free” state between the CT state and free charges is proposed and subsequently shown to fit the MC data very well. The predictive capability of the modified model was then tested by repeating MC simulations with an altered recombination rate. It is shown that more than just the recombination rate had to be changed in the modified kinetic model to retrieve good agreement with MC simulations. This suggests that the derived rates from the modified kinetic model do not have exact correspondence with physical processes in organic photovoltaic blends. We attribute the difficulty in fitting kinetic models to CT recombination data to the dispersive nature of hopping transport.

Item Type:Article
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Available under License - Creative Commons Attribution.
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Status:Peer-reviewed
Publisher Web site:http://dx.doi.org/10.1021/jp408063f
Publisher statement:This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.
Date accepted:24 September 2014
Date deposited:18 March 2014
Date of first online publication:09 January 2014
Date first made open access:No date available

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