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Singlet Fission and Triplet Exciton Dynamics in Rubrene/Fullerene Heterojunctions: Implications for Electroluminescence
Author(s) -
Ullah Mujeeb,
Yambem Soniya D.,
Moore Evan G.,
Namdas Ebinazar B.,
Pandey Ajay K.
Publication year - 2015
Publication title -
advanced electronic materials
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.25
H-Index - 56
ISSN - 2199-160X
DOI - 10.1002/aelm.201500229
Subject(s) - rubrene , singlet fission , electroluminescence , materials science , exciton , heterojunction , fullerene , singlet state , optoelectronics , fission , photochemistry , nanotechnology , condensed matter physics , atomic physics , excited state , physics , chemistry , layer (electronics) , quantum mechanics , neutron
The role of triplet excitons in rubrene/C 60 heterojunctions is investigated through detailed spectroscopic studies of triplet generation routes in the neat and heterojunction films of rubrene and C 60 . Time‐correlated single‐photon counting experiments on rubrene and rubrene/C 60 give a long‐lived component with lifetime >200 ns, and triplets are found to live longer in rubrene/C 60 . A distinct reduction at short time scales in fluorescence lifetime of rubrene/C 60 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/C 60 occurs at t ≈ 8 ps. The slow rise of triplet population confirms the role of CT‐state‐mediated triplet energy transfer in rubrene/C 60 . The recombination of triplets via triplet–triplet annihilation in organic light‐emitting diode (OLED) operation of rubrene/C 60 is shown to generate extra singlets, which lift the spin branching ratio to values >25%. It is concluded that triplet excitons in rubrene/C 60 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.