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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]

In order to develop novel pyrene-derived thermally activated delayed fluorescence (TADF) materials and deeply study their structure–property relationship, two emitters of PyPzCN-TPA2 and PyQlCN-TPA2 were designed and synthesized by alternating dicyano pyrenopyrazine (PyPzCN) and dicyano pyrenoquinoxaline (PyQlCN) as the rigid electron-deficient skeleton, as well as triphenylamine (TPA) as an electron-rich unit anchored at the K-region of pyrene, respectively. The effects of the rigid electron-deficient skeleton and electron-rich unit on photophysical and electroluminescence (EL) properties were primarily studied. The extending rigid electron-deficient skeleton made PyQlCN-TPA2 exhibit red-shifted emission at 658 nm in toluene and 840 nm in its neat film. The appending electron-rich unit at the K-region made both emitters exhibit large steric hindrance with a torsion angle of more than 70°, which resulted in a small ΔEST value of about 0.032 eV and a high kRISC of about 1.6–4.7 × 105 s−1. As a result, the solution-processed PyPzCN-TPA2 and PyQlCN-TPA2-doped OLEDs simultaneously exhibited high EQEs of 9.30% at 588 nm and 8.94% at 630 nm, respectively. The EQE roll-off was efficiently suppressed with an increase of emission wavelength. This is the first time that high-efficiency red-emitting pyrene-derived TADF materials were obtained by extending the rigid electron-deficient skeleton and appending the electron-rich unit at the K-region for solution-processed OLEDs. [ABSTRACT FROM AUTHOR]

Organic near-infrared (NIR) phosphorescent materials, especially platinum complexes, still attract the attention of researchers due to their excellent performance. However, most of the high-efficiency mononuclear cyclometalated platinum complexes in NIR-OLEDs are derived from intermolecular excimer emission except for porphyrin–platinum complexes. The problem is that aggregated emission heavily relies on solid-state packaging technology, which poses challenges to preparation conditions and performance optimization of devices. Employing dinuclear platinum complexes as dopants for solution processed devices is regarded as one of the methods to solve this problem and achieve intrinsic long wavelength emission. Here, we report a class of dinuclear platinum complexes Pt1 and Pt2 which have a butterfly-shaped three-dimensional structure and a cyano (CN) group on the main ligand. Importantly, maximum external quantum efficiencies (EQEmax) of 2.73% and 2.62% around 780 nm at a low doping concentration of 2.0 wt% were achieved for Pt1 and Pt2 based NIR-OLEDs. Our results demonstrate that butterfly shaped dinuclear platinum complexes obtained by cyanidation can be potential candidates for achieving solution processed long wavelength NIR-OLEDs. [ABSTRACT FROM AUTHOR]

Efficient host materials with a bipolar charge transport character have attracted much attention of both academic and industrial communities. In this contribution, dipole moment engineering is proposed to transform a classical hole-type host material (o-CBP) into a bipolar organic light-emitting diode (OLED) host material via introducing nitrogen (N) heteroatom atoms. Thus, 2,2′-di(9H-carbazol-9-yl)-3,3′-bipyridine (o-CBPy) and 9-(3-(2-(9H-carbazol-9-yl-)phenyl)pyridin-2-yl)-9H-carbazole (o-CPPy) are designed and prepared. After introduction of N atom(s), both novel host materials possess a large charge-transfer dipole moment, which is favorable for bipolar transport. Relatively high thermal stability and triplet energy states are obtained for compounds o-CBPy and o-CPPy , and o-CBPy possesses a charmingly balanced charge-transport property as well. Impressively, both sky-blue and green phosphorescent OLEDs employing o-CBPy as the host matrix show very a high efficiency (>30%) and small efficiency roll-off. The white OLEDs based on o-CBPy also exhibit an EQEmax of 25.5% and a color rendering index (CRI) of 76. This research demonstrates that dipole moment engineering is an effective strategy for designing high efficiency bipolar host materials for OLEDs. [ABSTRACT FROM AUTHOR]

In this study, for the first time, a novel low-cost halogen-free supramolecular additive, namely 5-hydroxy-2-methylpyrimidine (ROPD), has been applied to control the morphology of the PTB7-Th:PC71BM active layer, resulting in higher power conversion efficiency (PCE) value, as well as substantially increased thermal stability compared with the classic 1,8-diiodooctane (DIO) additive. The introduction of the ROPD additive brings an enhanced molar extinction coefficient, higher carrier transporting ability, as well as better nanoscale phase-separated morphology, which is ascribed to the interaction with both PTB7-Th and PC71BM through π–π or/and hydrogen bonding, and confirmed by FT-IR, 1H NMR and XRD spectra. Encouragingly, even without thermal annealing (TA) and solvent vapor annealing (SVA) treatments, the PCE of a specimen processed with the ROPD additive improved from 7.40% to 8.33%, getting close to the enhanced 13% of its initial value. In contrast, using the 1,8-diiodooctane (DIO) solution additive in the PTB7-Th:PC71BM-based device only results in an increase from 7.40 to 7.86%. In particular, after successive 60 °C thermal annealing for 210 h illumination, the trend of approaching 84.2% of the original efficiency was still maintained, and more than 76.1% and 55.6% was achieved with and without the DIO additive, respectively. These findings reveal that the smart utilization of a simple halogen-free solid additive by inducing hydrogen bonding is a promising approach for fabricating highly efficient and stable PSCs. [ABSTRACT FROM AUTHOR]

To reveal the influences of introducing various end-capping units onto small-molecule (SM) donors, in this article, 2-octylthio-thiophene (TS), 2-octyl-thiazole (TZ) and 2-octylthiothiazole (TZS) are strategically selected as end-capping units to combine with a fluorinated 2,2′-bithiophene (FBT) core and thiophene-flanked diketopyrrolopyrrole (TDPP) units as electron acceptors to afford three novel D(A–Ar)2 type SM donors, namely FBT(TDPP-TS)2, FBT(TDPP-TZ)2 and FBT(TDPP-TZS)2. The structure-property relationships provoked by slight changes in the terminal groups were systematically evaluated. In particular, TZS end-units make FBT(TDPP-TZS)2 possess better molecular stacking, higher mobility and better miscibility in the blend with PC71BM in comparison with the other two SMs. As a result, the introduction of TZS end-groups has been found to enhance the open-circuit voltage (Voc), short circuit current density (Jsc) and fill factor (FF) simultaneously. After optimization, an outstanding power conversion efficiency (PCE) of 8.91% with a Voc of 0.80 V, a Jsc of 16.75 mA cm−2 and a FF of 66.93% was obtained for the FBT(TDPP-TZS)2 based device, which is among the top values of the D(A–Ar)2 type single junction small molecular BHJ-OSCs. Our results obtained here indicate that strategic hetero-substitution of end-capping units in D(A–Ar)2 type SMs is an efficient strategy to improve photovoltaic performance. [ABSTRACT FROM AUTHOR]

The use of electron-withdrawing substituents on the orthometalated phenyl ring is a common strategy to blue shift the emission of cyclometalated iridium complexes by stabilizing the highest occupied molecular orbital (HOMO), that is, increasing the oxidation potential of the complex. However, for application in blue organic light-emitting diodes (OLEDs), this approach imposes host materials with a deep HOMO, which negatively impacts the injection of charges, and hence the performance of the devices. In this context, we report new iridium complexes with an electron-donating substituent on the cyclometalated ligand to blue shift the emission while keeping a relatively low oxidation potential. As a result, bluish-green OLEDs based on host materials with shallow HOMOs (TCTA = 4,4′,4′′-tri(N-carbazolyl)-triphenylamine) display a higher performance than devices using FIrpic in the same architecture. The improvements are primarily attributed to the lower turn-on voltage (2.8 to 3 V) compared to those of FIrpic-device (3.6 V). White OLED was then prepared with a maximum brightness of 20 226 cd m−2 and current efficiency of 20.4 cd A−2 (at 100 cd m−2). Interestingly, a very small efficiency roll-off of about 1% at 1000 cd m−2 and high color stability were achieved. At a luminance level of 5000 cd m−2 the roll-off efficiency was still below 20%. The introduction of electron-donating substituents on a 2-phenylpyridine scaffold to obtain blue emitters with low oxidation potentials provides an alternative to strategies based on replacing the pyridine with imidazole, carbene, and pyrazole. [ABSTRACT FROM AUTHOR]