Correlation Between Triplet–Triplet Annihilation and Electroluminescence Efficiency in Doped Fluorescent Organic Light‐Emitting Devices

Abstract

Triplet–triplet annihilation (TTA) is studied in a wide range of fluorescent host:guest emitter systems used in organic light‐emitting devices (OLEDs). Strong TTA is observed in host:guest systems in which the dopant has a limited charge‐trapping capability. On the other hand, systems in which the dopant can efficiently trap charges show insignificant TTA, an effect that is due, in part, to the efficient quenching of triplet excitons by the trapped charges. Fluorescent host:guest systems with the strongest TTA are found to give the highest OLED electroluminescence efficiency, a phenomenon attributed to the role of TTA in converting triplet excitons into additional singlet excitons, thus appreciably contributing to the light output of OLEDs. The results shed light on and give direct evidence for the phenomena behind the recently reported very high efficiencies attainable in fluorescent host:guest OLEDs with quantum efficiencies exceeding the classical 25% theoretical limit.

Triplets Contribute to Both an Increase and Loss in Fluorescent Yield in Organic Light Emitting Diodes

“…Recently, two types of excitonic interactions, triplet-triplet annihilation (TTA), and singlet-triplet annihilation (STA) were separately found to significantly influence the efficiency of fluorescent OLEDs. TTA [5,6] can generate singlets, thus increasing the theoretical limit of the IQE from 25%, to a maximum of 62.5% [3,[7][8][9]. On the other hand, STA [10,11] reduces the singlet density, thereby lowering the efficiency by as much as 50% at high brightness [12,13].…”

A Theoretical Study of the Formation of Benzene Excimer: Effects of Geometry Relaxation and Spin-state Dependence

“…2,3,8,10,[16][17][18][19][20][21][22][23][24][25][26] As for recent theoretical studies of intermolecular interactions in the excited states, various acene molecules including benzene were employed. 9,18,[20][21][22][24][25][26][27] Most of those studies, however, rely on the frozen molecular structures derived from the ground-state calculations and thus the geometric relaxation effects have been neglected. In this regard, it is demanding to assess how much the structures are deformed in the excited state and investigate what impacts they have.…”

“…However, triplet state dynamics also play an essential role in organic electronics; [8][9][10][11] for example, triplet exciton is the major product in organic light emitting diodes (OLEDs) and triplet-triplet annihilation is believed to be one of the main phenomena to influence OLED efficiency. 27,28 Furthermore, the conversion between singlet and triplet states in large depends upon the energy difference of these states.…”

Optimizing the Charge Balance of Fluorescent Organic Light‐Emitting Devices to Achieve High External Quantum Efficiency Beyond the Conventional Upper Limit

“…One possible mechanism causing the high EQE is triplet-triplet annihilation (TTA). [15][16][17][18][19] Transient electroluminescence responses of the green and blue emitting devices are shown in Figure 5 . In both the green and blue emitting devices, the …”