Student: Tengiz Kardava Department of Physics, IV Course, GTU Supervisor: Prof. PAATA KERVALISHVILI Triplet emitters for OLEDs: Introduction to exciton formation, charge transfer states, and triplet harvesting Department of Physics
Organo-transition-metal triplet emitters …
which lead to electron-hole recombination (exciton formation) and to the population of the emissive triplet states is presented.
In particular, it is shown that the dynamical process of exciton formation and trapping on an emitter molecule involves charge transfer states which result from excitations of the dopant to its nearest neighbor matrix environment.
Only the singlet state can emit radiatively (fluorescence). On the other hand, in organo-transition- metal compounds, fast intersystem crossing induced by spin-orbit coupling effectively depopulates the excited singlet into the lowest triplet state. Again due to SOC, the triplet can decay radiatively as phosphorescence even with high emission quantum yield at ambient temperature. In case of validity of spin statistics only 25% of the excitons can be exploited by organic emitters, while for triplet emitters additional 75% of the excitons are harvested.
Light emission in an electro- luminescent Thus, the efficiency of light emission in an electro-luminescent device with triplet emitters can be by a factor of four higher than with singlet emitters.