Interfacial exciton-polaron quenching (EPQ) in organic light-emitting diodes (OLED) refers to the remote and direct energy transfer from the excitons in the emission layer (EML) to the charges accumulated at the interface of the adjacent charge transport layers (CTLs). Here, interfacial EPQ is investigated by using a bilayer hole-only device (HOD), where an ultra-thin dopant layer is selectively introduced near the interface. At the heterointerface, positive-charge accumulation is induced due to the energy difference between distinct organic layers, while excitons are optically pumped in the dopants exclusively. The interfacial EPQ is characterized by measuring a shift in the photoluminescent intensity of the dopants. Such interfacial EPQ indeed depends on the interfacial energy offset and the distance between charges and excitons, and universally occurs regardless of the emission mechanism of OLEDs. We propose the device architecture to potentially reduce interfacial EPQ for achieving high-performance OLEDs.
Recently all-organic thermally activated delayed fluorescent (TADF) emitters have attracted great attention. In TADF emitters, nonemissive triplet states can be also harvested via population of emissive singlet states through reverse intersystem crossing (RISC). The RISC can be induced by the small energy gap between the lowest singlet (S1) and triplet (T1) states. Due to this ability of TADF, 100% internal quantum efficiency and high maximum external quantum efficiency (EQEmax) comparable to those of phosphorescent organic light emitting diodes (OLEDs) have been already reported in TADF OLEDs. In this study, we demonstrate high efficiency TADF OLEDs which are attributed to employing triazine acceptor type TADF compounds having high RISC rates(kRISC).
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