The role of spin in the degradation of organic photovoltaics

Ivan Ramirez, Alberto Privitera, Safakath Karuthedath, Anna Jungbluth, Johannes Benduhn, Andreas Sperlich, Donato Spoltore, Koen Vandewal, Frédéric Laquai, Moritz Riede

Research output: Contribution to journalArticlepeer-review

9 Scopus citations

Abstract

AbstractStability is now a critical factor in the commercialization of organic photovoltaic (OPV) devices. Both extrinsic stability to oxygen and water and intrinsic stability to light and heat in inert conditions must be achieved. Triplet states are known to be problematic in both cases, leading to singlet oxygen production or fullerene dimerization. The latter is thought to proceed from unquenched singlet excitons that have undergone intersystem crossing (ISC). Instead, we show that in bulk heterojunction (BHJ) solar cells the photo-degradation of C60 via photo-oligomerization occurs primarily via back-hole transfer (BHT) from a charge-transfer state to a C60 excited triplet state. We demonstrate this to be the principal pathway from a combination of steady-state optoelectronic measurements, time-resolved electron paramagnetic resonance, and temperature-dependent transient absorption spectroscopy on model systems. BHT is a much more serious concern than ISC because it cannot be mitigated by improved exciton quenching, obtained for example by a finer BHJ morphology. As BHT is not specific to fullerenes, our results suggest that the role of electron and hole back transfer in the degradation of BHJs should also be carefully considered when designing stable OPV devices.
Original languageEnglish (US)
JournalNature Communications
Volume12
Issue number1
DOIs
StatePublished - Jan 20 2021

Bibliographical note

KAUST Repository Item: Exported on 2021-02-03
Acknowledged KAUST grant number(s): OSR-2018-CARF/CCF-3079
Acknowledgements: We thank Dr. Olaf Zeika for TPDP synthesis, Dr. Josue Martinez-Hardigree for his insights on morphology, and Professor Natalie Banerji for her valuable advice with TA analysis. A.P. thanks Dr. William Myers and the Centre for Advanced ESR (CAESR) located in the Department of Chemistry of the University of Oxford (supported by EPSRC EP/L011972/1). I.R. thanks TU Dresden technicians for help with sample production and Dr. Frederik Nehm for help with device degradation. This work was supported by European Union’s Horizon 2020 research and innovation program under Marie Sklodowska Curie Grant agreement number 722651 (SEPOMO) and by the COST Action MP1307 (StableNextSol). M.R. acknowledges funding from an EU FP7 Marie Curie Career Integration Grant (number PCIG14-GA-2013-630864) and STFC Challenge Led Applied Systems Programe (CLASP, Grant number ST/L006294/1). This publication is based upon work supported by the King Abdullah University of Science and Technology (KAUST) Office of Sponsored Research (OSR) under award number OSR-2018-CARF/CCF-3079.

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