Enhancing the efficiency of organic LEDs through spin-orbit coupling of charge-transfer states
Author(s)Rivoire, Kelley (Kelley E.)
Massachusetts Institute of Technology. Dept. of Physics.
Marc A. Baldo.
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In this thesis, the possibility of enhancing the efficiency of small molecule organic light-emitting diodes through spin-orbit effects is examined. Because only singlet spin states, statistically one quarter of the total possible states, emit fluorescent light, it has generally been thought that a maximum of 25% efficiency could be attained without the addition of an emissive phosphor. Here, we present evidence that this is not a fundamental limit. Two OLED structures have been studied, each providing evidence that the efficiency of the OLED can be enhanced by the use of a heavy-metal material to mix spin in charge-transfer states. A structure with a heavy-metal mixing layer placed beside a neat emissive layer was found to show a (2.5 ± 0.3) times enhancement in the efficiency compared with an OLED without the heavy-metal layer. However, differences in the electroluminescent emission spectra made attributing this result to spin statistics alone difficult. In a structure with the the heavy-metal mixing layer placed next to a fluorescent dye doped into a host, a (2.7 ± 0.2) times enhancement in the efficiency is measured.
Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Physics, 2006.Includes bibliographical references (p. 59-63).
DepartmentMassachusetts Institute of Technology. Dept. of Physics.
Massachusetts Institute of Technology