Buildup of Triplet-State Population in Operating TQ1:PC71BM Devices Does Not Limit Their Performance

Safakath Karuthedath, Julien Gorenflot, Armantas Melianas, Zhipeng Kan, Martijn Kemerink, Frédéric Laquai

Research output: Contribution to journalArticlepeer-review

26 Scopus citations


Triplet generation in organic solar cells has been considered a major loss channel. Determining the density of the triplet-state population in an operating device is challenging. Here, we employ transient absorption (TA) spectroscopy on the quinoxaline–thiophene copolymer TQ1 blended with PC71BM, quantify the transient charge and triplet-state densities, and parametrize their generation and recombination dynamics. The charge recombination parameters reproduce the experimentally measured current–voltage characteristics in charge carrier drift-diffusion simulations, and they yield the steady-state charge densities. We demonstrate that triplets are formed by both geminate and nongeminate recombination of charge carriers and decay primarily by triplet–triplet annihilation. Using the charge densities in the rate equations describing triplet-state dynamics, we find that triplet-state densities in devices are in the range of charge carrier densities. Despite this substantial triplet-state buildup, TQ1:PC71BM devices exhibit only moderate geminate recombination and significantly reduced nongeminate charge recombination, with reduction factors between 10–4 and 10–3 compared to Langevin recombination.
Original languageEnglish (US)
Pages (from-to)2838-2845
Number of pages8
JournalThe Journal of Physical Chemistry Letters
Issue number8
StatePublished - Mar 23 2020

Bibliographical note

KAUST Repository Item: Exported on 2020-10-01
Acknowledgements: This publication is based upon work supported by the King Abdullah University of Science and Technology (KAUST) Office of Sponsored Research (OSR) under Award No: OSR2018-CARF/CCF-3079. The authors thank Dr. Fabian Etzold for the reference spectra of triplets and charges in TQ1. A.M. gratefully acknowledges support from the Knut and Alice Wallenberg Foundation (KAW 2016.0494) for Postdoctoral Research at Stanford University


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