Journal
PHYSICAL REVIEW LETTERS
Volume 108, Issue 26, Pages -Publisher
AMER PHYSICAL SOC
DOI: 10.1103/PhysRevLett.108.267404
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Funding
- U.S. Department of Energy, Center for Energy Nanoscience at the University of Southern California [DE-SC0001013]
- Air Force Office of Scientific Research
- Small Business Innovation Research program
- U.S. Department of Energy through Universal Display Corporation (SRF)
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Nonradiative triplets in fluorescent organic light emitting diodes (OLEDs) can lead to increased efficiency through triplet-triplet annihilation, or to decreased efficiency due to singlet-triplet annihilation. We study the tradeoff between the two processes from the electroluminescence transients of an OLED comprising a tetraphenyldibenzoperiflanthene (DBP) doped rubrene emissive layer, whose emission spectrum peaks at a wavelength of 610 nm. The electroluminescent transients in the current density range, 4 m Lambda/cm(2) < J < 57 Lambda=cm(2), are modeled based on singlet and triplet density dynamics. Our analysis shows that triplets positively contribute to the OLED efficiency at J < 2.2 Lambda/cm(2), while decreasing the efficiency at higher J. The high OLED peak external quantum efficiency of 6.7% and rapid efficiency roll-off with J are quantitatively explained by the tradeoff between triplet-triplet and singlet-triplet annihilation. The model suggests optimal materials properties needed for achieving high efficiency at high brightness in fluorescent OLEDs.
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