Singlet Fission and Triplet Exciton Dynamics in Rubrene/Fullerene Heterojunctions: Implications for Electroluminescence.

Ullah, Mujeeb; Yambem, Soniya D.; Moore, Evan G.; Namdas, Ebinazar B.; Pandey, Ajay K.

Abstract

The role of triplet excitons in rubrene/C60 heterojunctions is investigated through detailed spectroscopic studies of triplet generation routes in the neat and heterojunction films of rubrene and C60. Time-correlated single-photon counting experiments on rubrene and rubrene/C60 give a long-lived component with lifetime >200 ns, and triplets are found to live longer in rubrene/C60. A distinct reduction at short time scales in fluorescence lifetime of rubrene/C60 gives the indication of singlet exciton dissociation via formation of charge-transfer (CT) states. Using ultrafast transient absorption spectroscopy, it is found that triplets are generated via singlet-fission in neat rubrene films at t ≈ 1.8 ps, whereas a delayed population buildup of triplets in rubrene/C60 occurs at t ≈ 8 ps. The slow rise of triplet population confirms the role of CT-state-mediated triplet energy transfer in rubrene/C60. The recombination of triplets via triplet–triplet annihilation in organic light-emitting diode (OLED) operation of rubrene/C60 is shown to generate extra singlets, which lift the spin branching ratio to values >25%. It is concluded that triplet excitons in rubrene/C60 are instrumental in bringing lower turn-on voltages, brighter emission, and higher external quantum efficiency of electroluminescence in OLED and light-emitting field effect transistors.

Citation

Ullah, M., Yambem, S. D., Moore, E. G., Namdas, E. B., & Pandey, A. K. (2015). Singlet Fission and Triplet Exciton Dynamics in Rubrene/Fullerene Heterojunctions: Implications for Electroluminescence. Advanced Electronic Materials, 1(12), Article 1500229. https://doi.org/10.1002/aelm.201500229

• Journal Article Type: Article
• Acceptance Date: Jul 15, 2015
• Online Publication Date: Oct 28, 2015
• Publication Date: 2015-12
• Deposit Date: Apr 13, 2017
• Journal: Advanced Electronic Materials
• Publisher: Wiley
• Peer Reviewed: Peer Reviewed
• Volume: 1
• Issue: 12
• Article Number: 1500229
• DOI: https://doi.org/10.1002/aelm.201500229