4.8 Article

The Role of Balancing Carrier Transport in Realizing an Efficient Orange-Red Thermally Activated Delayed-Fluorescence Organic Light-Emitting Diode

Journal

ACS APPLIED MATERIALS & INTERFACES
Volume 14, Issue 47, Pages 53120-53128

Publisher

AMER CHEMICAL SOC
DOI: 10.1021/acsami.2c17492

Keywords

thermally activated delayed fluorescence; organic light-emitting diodes; carrier mobility; carrier balance; orange-red emission

Funding

  1. National Natural Science Foundation of China
  2. [U2001222]
  3. [21975055]

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The synthesis of two isomeric orange-red TADF emitters with similar good PL properties and the demonstration of higher quantum efficiency in an orange-red OLED using oPDM as the emitter suggest the importance of balanced carrier-transporting properties in achieving improved device performance in TADF emitters.
Simultaneously realizing improved carrier mobility and good photoluminescence (PL) efficiency in red thermally activated delayed-fluorescence (TADF) emitters remains challenging but important. Herein, two isomeric orange-red TADF emitters, oPDM and pPDM, with the same basic donor-acceptor backbone but a pyrimidine (Pm) attachment at different positions are designed and synthesized. The two emitters show similarly good PL properties, including narrow singlet-triplet energy offsets (0.11 and 0.15 eV) and high photoluminescence quantum yields (ca. 100 and 88%) in doped films. An orange-red organic light-emitting diode (OLED) employing oPDM as an emitter achieves an almost twice as high maximum external quantum efficiency (28.2%) compared with that of a pPDM-based OLED. More balanced carrier-transporting properties are responsible for their contrasting device performances, and the position effect of the Pm substituent lends to significantly distinct molecular packing behaviors in the aggregate states and different carrier mobilities.

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