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Multiple resonance thermally activated delayed fluorescence (MR-TADF) emitters have been widely used for highly efficient and ultrapure organic light-emitting diodes (OLEDs) via thermal deposition, while the low-cost solution procedure still remains underexplored. Herein, we propose a TADF polymer as the sensitizer of a narrowband emitter to fabricate solution-processed MR-TADF OLEDs. Due to the effective harvesting of triplet excitons, the sensitized devices based on TADF polymer achieve a narrowband electroluminescence, revealing a maximum external quantum efficiency (EQEmax) of 15.7% together with CIE coordinates of (0.28, 0.65). The performance is approximately 2 times higher than that of non-sensitized devices (7.0%), highlighting the great potential of TADF polymers in efficient solution-processed MR-TADF OLEDs. [ABSTRACT FROM AUTHOR]

Solution‐processed fluorescent organic light‐emitting diodes (OLEDs) are believed to be favorable for low‐cost, large‐area, and flexible displays but still suffer from the limited external quantum efficiency (EQE) below 5%. Herein, we demonstrate the EQE breakthrough by introducing a donor–acceptor type thermally activated delayed fluorescence (TADF) polymer as the sensitizer for the typical green‐emitting fluorescent dopants. Benefitting from their matched energy alignment, the unwanted trap‐assisted recombination directly on fluorescent dopant is prevented to avoid the additional loss of triplet excitons. Indeed, triplet excitons are mainly formed on the polymeric TADF sensitizer via a Langevin recombination and then spin‐flipped to singlet excitons due to the good upconversion capability. Followed by an efficient Förster energy transfer, both singlet and triplet excitons can be harvested by fluorescent dopants, leading to a promising solution‐processed green hyperfluorescence with a record‐high EQE of 21.2% (72.2 cd/A, 59.7 lm/W) and Commission Internationale de L'Eclairage coordinates of (0.32, 0.59). The results clearly highlight the great potential of solution‐processed fluorescent OLEDs based on TADF polymers as the sensitizer. [ABSTRACT FROM AUTHOR]

It remains a significant challenge to develop organic room-temperature electrophosphorescence. In this work, we develop two organic phosphors D31 and D32 with acridine as the electron donor, benzophenone with different connection positions as the electron acceptor, and oxygen atom as the bridge. The insertion of the oxygen atom would effectively facilitate the intersystem crossing (ISC) and phosphorescence processes. Due to the different connection positions of benzophenone, D31 and D32-based non-doped devices exhibit an aggregation-diminished and aggregation-enhanced organic room temperature electrophosphorescence with the maximum external quantum efficiency (EQEmax) of 4.51% and 6.70%, respectively. Moreover, the host-free sensitization device based on D32 and S-Cz-BN revealed a significantly boosted EQEmax of 17.11% with a small full-width at half maximum (FWHM) of 28 nm. This work provides a novel approach to develop highly efficient aggregation-induced organic room temperature electrophosphorescence. [ABSTRACT FROM AUTHOR]

Selenium incorporation is a widely used strategy for achieving high mobility semiconductors for a variety of organic optoelectronic devices, but it has received less attention in organic electrochemical transistors (OECTs). Herein, we developed two polythiophene derivatives (Pg2T-S and Pg2T-SVS) containing different selenophene loadings, as well as a selenophene-free polythiophene (Pg2T-T) as the control. The effects of selenium substitution/incorporation on the optical, electrical, electrochemical, and OECT performance of polythiophene-based organic mixed ionic–electronic conductors are systematically investigated. We discovered that introduction of selenium increases quinoidal character and crystallinity, which is beneficial for charge transport but makes ion penetration more challenging. In contrast, increasing selenium content increases the dipole moment and ion–polymer interaction, which is helpful for ion doping and volumetric capacitance but detrimental to charge transport. Therefore, appropriate selenium content should be evaluated to balance the trade-off between charge transfer and volumetric capacitance. As a result, Pg2T-S with moderate selenium loading achieves a high μC* of 332.7 F cm−1 V−1 s−1 with increased μ of 1.31 cm2 V−1 s−1 and maintains the C* value of 254 F cm−3. It also has a quick τon/τoff of 10.76 ms/5.90 ms and outstanding operational stability. Further introducing selenium boosts the dipole moment and ion–polymer interaction and therefore increased C*, but suppressed μ, resulting in inefficient μC*. We indicated that systematic balancing of the effects of selenium incorporation is necessary for the development of mixed ionic–electronic conductors for high-performance OECTs. [ABSTRACT FROM AUTHOR]