Interacting Emission Species among Donor and Acceptor Moieties in a Donor-Grafted Polymer Host/TADF-Guest System and Their Effects on Photoluminescence and Electroluminescence

• Published in: ACS applied materials & interfaces Vol. 16; no. 44; pp. 60715 - 60731
• Main Authors: Mao, Yi-Hen, Hung, Miao-Ken, Chung, Shang-Ting, Sharma, Sunil, Tsai, Kuen-Wei, Chen, Show-An
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society 06.11.2024
• Subjects: color; electrochemiluminescence; energy transfer; fluorescence; Organic Electronic Devices; photoluminescence; polymers; species; intramolecular charge transfer (ICT); exciplex; thermally activated delayed fluorescence (TADF); organic light-emitting diode (OLED); excimer; polymer light-emitting diode (PLED); aggregate; donor−acceptor (D−A)
• ISSN: 1944-8244; 1944-8252; 1944-8252
• DOI: 10.1021/acsami.4c15933

Thermally activated delayed fluorescence (TADF)-based electroluminescence (EL) devices adopting a host/guest strategy in their emitting layer (EML) are capable of realizing high efficiency. However, TADF emitters composed of donor and acceptor moieties as guests dispersed in organic host materials containing a donor and/or an acceptor are subject to donor–acceptor (D–A) interactions. In addition, electron delocalization between neighboring emitter molecules could form different species of aggregates. Here, we investigate the effects of intermolecular interacting emission species on the optoelectronic properties of sky-blue/green/red (sB/G/R) TADF emitters as guests using poly­(biphenyl-Si/Ge) grafted with various donor moieties as hosts. We found the presence of guest/guest exciplex (Dg/Ag)*, host/guest exciplexes (Dh/Ag)*, and aggregates through the exploration of interactions between neighboring TADF guest molecules and between host and TADF-guest molecules. The nonradiative 3(Dh/Ag)* (ΔE ST ≈ 0.5 eV) could increase the internal conversion rate (kIC) and reduce delayed luminescence, and both of them could cause a decrease in PLQY. The luminescence of 3(Dh/Ag)* may have a positive or negative effect on PLQY depending on its triplet energy. As the singlet and triplet energies of (aggregate)* are lower than those of (ICT)*, energy transfer from (ICT)* to (aggregate)* could occur. The low PLQY nature of (aggregate)* means that it is more likely to cause quenching in device emission. The emissions from (Dh/Ag)* and (aggregate)* are found to have increased full width at half-maximum and lead to lower emission color purity. Such intermolecular interactions should also occur in host/guest (TADF) systems and nondoped TADF emitter systems and thus are important factors for the molecular design of the TADF emitter and/or its accompanying host for high device efficiency and emission color purity.