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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]

Single‐component ambipolar polymers are highly desirable for organic electrochemical transistors (OECTs) and integration into complementary logic circuits with reduced process complexity. However, they often suffer from imbalanced p‐type and n‐type characteristics and/or stability issues. Herein, a novel single‐component ambipolar polymer, namely, gIDT–BBT is reported based on indacenodithiophene (IDT) as the electron donor, benzobisthiadiazole (BBT) as the electron acceptor and oligo ethylene glycol (OEG) as the side chain. Benefitting from the extended backbone planarity and rigidity of IDT, pronounced electron‐withdrawing capability of BBT, favored ionic transport from OEG together with vertical OECT device structure, a nearly balanced ambipolar OECT performance is achieved for gIDT–BBT, revealing a high transconductance of 155.05 ± 1.58/27.28 ± 0.92 mS, a high current on/off ratio >106 and an excellent operational stability under both p‐type and n‐type operation conditions. With gIDT–BBT in hand, furthermore, vertically stacked complementary inverters are successfully fabricated to show a maximum voltage gain of 28 V V−1 (VIN = 0.9 V) and stable operation over 1000 switching cycles, and then used for efficient electrooculogram recording. This work provides a new approach for the development of ambipolar single‐component organic mixed ionic–electronic conductors and establishes a foundation for the manufacture of high‐performance ambipolar OECTs and associated complementary circuits. [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]

Thermally activated delayed fluorescence (TADF) polymers show a great potential in low‐cost, large‐area and flexible full‐color flat‐panel displays. One of the most promising design rules is based on TADF+Linker, where a small molecular TADF unit is bonded to each other by a simple linker. Unlike the expensive vacuum deposition for small molecules, these polymerized TADF small molecules (Poly‐TADF‐SMs) are capable of cost‐effective solution processing. Meanwhile, the good luminescent property of small molecular TADF emitters can be well inherited by Poly‐TADF‐SMs so as to bridge the efficiency gap between small molecules and polymers. Herein, we will highlight the recent progress of Poly‐TADF‐SMs, together with emphasis on their molecular design, photophysical and electroluminescence properties. [ABSTRACT FROM AUTHOR]

Nowadays numerous thermally activated delayed fluorescence (TADF) polymers have been developed for PLEDs to realize high device performance and tunable emission colors. However, they often possess a strong concentration dependence on their luminescence including aggregation‐caused quenching (ACQ) and aggregation‐induced emission (AIE). Herein, we first report a nearly concentration‐independent TADF polymer based on the strategy of polymerized TADF small molecules. It is found that when a donor‐acceptor‐donor (D‐A‐D) type TADF small molecule is polymerized through its long‐axis direction, the triplet state is distributed along the polymeric backbone to effectively suppress the unwanted concentration quenching. Unlike the short‐axis one with an ACQ effect, the photoluminescent quantum yield (PLQY) of the resultant long‐axis polymer remains almost unchanged with the increasing doping concentration. Accordingly, a promising external quantum efficiency (EQE) up to 20 % is successfully achieved in a whole doping control window of 5–100 wt. %. [ABSTRACT FROM AUTHOR]

Frontier molecular orbital engineering has been demonstrated to achieve aggregation-induced delayed fluorescence (AIDF) for non-doped OLEDs. As a proof of concept, a new model compound, AT-spiro-DMACF, is reported on the basis of the TXADO-spiro-DMACF reference by changing the spiro-linked moiety from thioxanthene dioxide to anthracen-9(10H)-one. Such a minor alteration makes the lowest unoccupied molecular orbital (LUMO) shift from the inner fluorene to the outer anthracen-9(10H)-one, while retaining the almost same highest occupied molecular orbital (HOMO) distribution. In this case, the intermolecular charge transfer between the HOMO and LUMO becomes favorable, leading to aggregation-induced emission and thermally activated delayed fluorescence. As a result of this AIDF nature, AT-spiro-DMACF achieves a good non-doped device performance with a peak external quantum efficiency of 9.8% (31.1 cd A−1, 33.7 lm W−1) and Commission Internationale de l'Eclairage coordinates of (0.35, 0.54). The result clearly indicates that frontier molecular orbital engineering is an effective strategy for the development of AIDF emitters that are suitable for non-doped OLEDs. [ABSTRACT FROM AUTHOR]

Solution-processed phosphorescent organic light-emitting diodes (PhOLEDs) have been known as promising alternatives to their vacuum deposited counterparts due to their excellent cost-effectiveness. However, the solution-processed devices still suffer from low efficiencies especially for the saturated red emission. Herein, we designed and demonstrated very efficient solution-processed red PhOLEDs by introducing a thermally activated delayed fluorescence (TADF) host with and without inert peripheral units, i.e., 4CzDMAC-DPS and DMAC-DPS respectively, to manipulate Förster and Dexter interactions. Compared with the steric hindrance on both the host and guest, Förster and Dexter energy transfers were simultaneously promoted when removing the hindrance units on the TADF host. This is mainly attributed to the larger radius of Förster energy transfer and closer intermolecular distance between DMAC-DPS and the guest, compared with those of the 4CzDMAC-DPS and guest system. As a result, the state-of-the-art solution-processed saturated red PhOLEDs achieved a high maximum external quantum efficiency (EQE) of 22.2% with an emission peak beyond 610 nm. In contrast, the TADF host with the additional hindrance units played an important role in achieving a low efficiency roll-off (< 10% at 1000 cd m−2) without sacrificing the EQE. Moreover, ternary-blended solution-processed PhOLEDs exhibited easy color tuning from red to white, which was dominated by the energy transfer radius mediated by the hindrance effect of the TADF compound. [ABSTRACT FROM AUTHOR]

Donor–acceptor (D–A) conjugated polymers often possess a significant frontier molecular orbital overlap because of the conjugation elongation, leading to no thermally activated delayed fluorescence (TADF) caused by a large singlet‐triplet energy splitting (▵EST). Herein a novel steric locking strategy is proposed by incorporating methyl groups into D–A conjugated polymers. Benefitting from the methyl hindrance, the torsion between the donor and acceptor can be well tuned to form a sterically‐locked conformation, so that the unwanted relaxation toward planarity and thus conjugation elongation is prevented to boost hole–electron separation. The resultant D–A conjugated polymer achieves an extremely low ΔEST of 0.09 eV to enable efficient TADF. The corresponding doped and non‐doped devices are fabricated via a solution process, revealing a record‐high external quantum efficiency (EQE) of 24.0 % (79.4 cd A−1, 75.0 lm W−1) and 15.3 % (50.9 cd A−1, 47.3 lm W−1). [ABSTRACT FROM AUTHOR]

A heterogeneous post-passivation process has been demonstrated by using formamidinium bromide (FABr) to compensate the surface bromo vacancy of inorganic cesium lead halide perovskite quantum dots (QDs). Benefitting from its limited solubility, the passivation is anticipated to happen in a two-phase heterogeneous mixture, and excess FABr can be easily removed using a polytetrafluoroethylene (PTFE) syringe filter before device fabrication. This is quite different from didodecyldimethylammonium bromide (DDAB)-based homogeneous post-passivation, where a large amount of DDAB residue is still left in the spin-coated film. Consequently, a more favorable electrical behavior is observed in FABr passivation compared to that in the DDAB one, although they both show comparable improved photoluminescence quantum yields due to bromo compensation. The corresponding perovskite quantum dots light-emitting diodes with FABr-treated green-emitting CsPbBr3 QDs achieve a promising external quantum efficiency (EQE) of 7.94% and luminance of 14 790 cd m−2, much higher than those of the pristine (1.78%, 4640 cd m−2) and the DDAB-treated samples (3.91%, 167 cd m−2). This methodology is also suitable for the surface defect passivation of blue-emitting CsPbBr1.3Cl1.7 and red-emitting CsPbBr1I2 QDs. The results clearly highlight that heterogeneous post-passivation can boost the photoluminescence and electroluminescence performance of inorganic cesium lead halide perovskite QDs simultaneously. [ABSTRACT FROM AUTHOR]

High‐performance red quantum dot light‐emitting diodes (QLEDs) are demonstrated based on nitrogen heterocycle‐containing compounds as the organic electron transporting layer (ETL). Unlike ZnO, the adoption of organic ETL can eliminate unwanted photoluminescence quenching of colloidal quantum dots (QDs) due to the prevented electron transfer between QDs and organic ETL. Most importantly, when the central core is varied from benzene and pyrimidine to triazine, their lowest unoccupied molecular orbital energy levels are found to be well tuned to facilitate electron injection. Consequently, a triazine‐cored organic ETL (denoted as TmPPPyTz) achieves a restored charge balance, giving a record‐high external quantum efficiency of 13.4% (18.8 cd A−1, 23.9 lm W−1) and Commission Internationale de l'Eclairage coordinates of (0.68, 0.32). The obtained state‐of‐art performance clearly indicates the great potential of organic ETL towards efficient QLEDs. [ABSTRACT FROM AUTHOR]

An electroactive room‐temperature phosphorescence (RTP) polymer has been demonstrated based on a characteristic donor‐oxygen‐acceptor geometry. Compared with the donor–acceptor reference, the inserted oxygen atom between donor and acceptor can not only decrease hole‐electron orbital overlap to suppress the charge transfer fluorescence, but also strengthen spin‐orbital coupling effect to facilitate the intersystem crossing and subsequent phosphorescence channels. As a result, a significant RTP is observed in solid states under photo excitation. Most noticeably, the corresponding polymer light‐emitting diodes (PLEDs) reveal a dominant electrophosphorescence with a record‐high external quantum efficiency of 9.7 %. The performance goes well beyond the 5 % theoretical limit for typical fluors, opening a new door to the development of pure organic RTP polymers towards efficient PLEDs. [ABSTRACT FROM AUTHOR]