Exciton–charge carrier interactions in the electroluminescence of crystalline anthracene

Abstract

The interactions of triplet excitons with trapped charge carriers are studied in anthracene single crystals. The triplet excitons are generated by the recombination of charge carriers through double injection. The lifetime of the triplet excitons is studied from the decay of the phosphorescence intensity in a transient measurement. The interaction rate constant for the trapped charge carriers is of the same order of magnitude as previous published data measured with single injection of electrons. It is further shown that the rate constant varies with different conditions of crystal growth. The simultaneous investigation of double injection delayed fluorescence reveals also a strong quenching of the delayed fluorescence from the excited singlet state by trapped charge carriers. Magnetic field measurements show that this quenching is partly due to an increased dissociation of the triplet pair state through the presence of charge carriers. The possibility of enhanced spin relaxation of the triplets in the pair state is also discussed.

Magnetic‐Field Effects in Organic Semiconducting Materials and Devices

“…[41,[106][107][108][109] This phenomenon indicates that nonmagnetic organic semiconductors have potential applications in spintronic devices where electronic, optical, and magnetic properties can be mutually controlled. On the other hand, the studies of MFE EL can enhance the critical understanding of intrinsic useful and non-useful excited processes in respective optoelectronic devices.…”

“…[82,[89][90][91][92] In addition, the triplet excitons can also react with free charge carriers in organic materials, with the outcome of dissociating e-h pairs. [93,94] The e-h separation was also shown in the MFEs on electroluminescence, where dissociated electrons and holes maintain their spin polarizations from their parent triplet excitons and the reform triplet excitons from their recombination. [95] This exciton-charge reaction can provide strong local electrical force to break strongly bound e-h pairs in excitonic states for the generation of charge carriers.…”

The role of magnetic fields on the transport and efficiency of aluminum tris(8-hydroxyquinoline) based organic light emitting diodes

“…If the carrier were to directly interact with the triplet state, then there would be spin selection rules to determine the final state and hence some field dependence would be expected. Subsequent work by Wittmer and Zschokke-Gränacher 14 showed that for free carrier interactions with triplet pairs, the effect of a magnetic field was to increase the rate constant for the dissociation of the combined state rather than to enhance the quenching of the triplet pair state into a singlet. Such an increase in the rate constant for dissociation, k 1 , would correspond to a reduction in the trapping time for carriers and, hence an increase in the mobility.…”

Large magnetic field effects in electrochemically doped organic light-emitting diodes

“…Due to the relatively large lifetime of triplet excitons, most likely their interaction with polarons is dominant. [33][34][35][36] The triplet exciton density itself is magnetic field dependent, which is followed from the change in singlet:triplet ratio as calculated in Fig. 5(a).…”