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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]

All-polymer solar cells (all-PSCs) have received tremendous focus recently owing to their superior mechanical robustness and excellent thermal stability. However, only few studies on the application of small-molecule acceptors (SMAs) in all-PSCs have been reported. Herein, a highly crystalline non-fused ring (NFR) SMA, namely DFTQA-2FIC, was introduced as a third component to enhance the performance of an all-PSC based on PBDB-T:N2200. After introducing DFTQA-2FIC into the PBDB-T:N2200 blend, the energy levels of DFTQA-2FIC did not only cascade with those of PBDB-T and N2200, but also formed a more uniform and continuous interpenetrating structure and caused better phase separation, thereby mitigating losses caused by electron–hole recombination, minimizing energy dissipation, and significantly elevating charge transport with a well-balanced performance. Encouragingly, an impressively improved power conversion efficiency (PCE) from 6.45% in binary all-PSCs to 8.07% in the ternary system, with an increase of 25.1%, was obtained, which is one of the highest reported for PBDB-T:N2200-based all-PSCs thus far. This study highlights the potential of this type of NFR-SMA as a third component for highly efficient ternary OSCs. [ABSTRACT FROM AUTHOR]

Chiral bipolar hosts of (R/S)- L -2mCPCN are synthesized, which show high singlet/triplet energy levels and clear circularly polarized luminescence. Employing racemic phosphorescent and TADF materials as emitting guest molecules, solution-processable CP-OLEDs based on such chiral hosts are obtained with an EQEmax of 10.7% and ‖gEL‖ values of 5.0 × 10−3. [ABSTRACT FROM AUTHOR]

Chiral liquid-crystalline emitters based on 9,9-dimethyl-10-(4-(phenylsulfonyl)phenyl)-9,10-dihydroacridine and a functionalised binaphthol show smectic liquid crystal phases and circularly polarised blue fluorescence with a high luminescence dissymmetry factor ‖glum‖ of 0.13. Solution-processable organic light-emitting diodes (OLEDs) based on the enantiomers were explored. [ABSTRACT FROM AUTHOR]

In organic solar cells (OSCs), the intricate synthesis and lower yield of ladder-type fused ring small molecule receptors (FR-SMAs) have prompted the quest for simpler, higher yielding non-fused ring (NFR)-SMAs. In this paper, a type of NFR asymmetrical SMA with an A–D–π–A structure, namely DPCT8-4F and DPCT10-4F, was primarily designed and synthesized, in which an alkyl chain dipyran (DP) ring, cycllopentadithiophene (CT) and fluorinated 1,1-dicyanomethylene-3-indanone (4F) are employed as the donor (D) unit, π-bridge and acceptor (A) terminals, respectively. The influence of the alkyl chain originating from the DP unit on their optical, electrochemical and photovoltaic properties was systematically investigated. The DPCT8-4F with n-octane chains exhibited enhanced crystallinity and molecular packing compared to the DPCT10-4F with n-decane chains. After being blended with the polymer donor PBDB-T, the OSCs based on PBDB-T:DPCT8-4F demonstrate an impressive power conversion efficiency (PCE) of 12.52%, surpassing that of 11.68% for the DPCT10-4F-based ones. This work demonstrates that these asymmetric NFR-SMAs can improve the efficiency of OSCs by pairing alkyl chains on the dipyran ring. [ABSTRACT FROM AUTHOR]

The moderate charge-transporting capability together with higher-lying energetic levels of self-assembling hole-transporting materials (SAMs) constrain the productive carrier extraction dynamics. To alleviate this issue, a synergetic chlorination and extended conjugation strategy is applied to explore a novel HTL, named 2Cl-TPA-CN-COOH. Indeed, the chlorinated head backbone would deepen the energetic level and strengthen the intramolecular push–pull effect, whereas the elongated conjugation unit would boost the carrier-transporting potential. Consequently, a champion power conversion efficiency (PCE) of 18.6% with upgraded stability is obtained in a 2Cl-TPA-CN-COOH cell. These results demonstrate a new insight of the molecular configuration of SAMs, which would contribute to the enhancements of performance and reliability in the OSC field. [ABSTRACT FROM AUTHOR]

Azaacenes have attracted wide research interest due to their tremendous potential in organic electronics. However, near-infrared (NIR) light-emitting iridium(III) phosphors bearing azaacene derivatives are rarely investigated. In this contribution, two solution-processable heteroleptic iridium(III) complexes, namely DBPzIr and PPzIr, are rationally designed and synthesized, and they contain a rigid phenanthrene- or pyrene-fused diazaacene core and two peripheral groups of 4-tert-butyl-phenyl attached at the 12,13-positions in the core, respectively. The effects of the diazaacene core and appending groups on the optoelectronic properties of both complexes are systematically investigated. A dramatically red-shifted NIR emission peak at 789 nm with a photoluminescence quantum yield (PLQY) of 14% is observed in PPzIr compared with the 746 nm emission with a PLQY of 40% in DBPzIr. Taking advantage of their photophysical properties, the solution-processed device doped with DBPzIr achieves a maximum external quantum efficiency (EQEmax) of 8.00% with a radiance of 54 866 mW Sr−1 m−2 at 716 nm and the device doped with PPzIr exhibits a significantly red-shifted emission at 772 nm with an EQEmax of 3.53%. The achieved device performance is among the best values in the reported NIR-OLEDs based on iridium(III) complexes via a solution process at the same color gamut. Our study indicates that the reasonable collocation of the rigid diazaacene chelating core and flexible peripheral groups in the iridium(III) complex is of great significance in designing highly efficient NIR emitters. [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]

Two kinds of chiral hosts, named (R/S)-BN-mCP and (R/S)-BN-2mCP, are prepared. Solution processable circularly polarized organic light-emitting diodes (CP-OLEDs) based on the chiral hosts and achiral emitter Ir(mypp)3 present the maximum external quantum efficiency (EQEmax) and dissymmetry factor values (gEL) of 12.7%/−1.7 × 10−3 and 17.1%/−1.3 × 10−3, respectively. Using (R)-BN-2mCP as the chiral host and Ir(mypp)3 and Ir(piq)2(acac) as the achiral emitters, the solution-processed OLED exhibits a broad emission spectrum with the EQEmax of 12.1% and gEL of −1.1 × 10−3. [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]

Multiple resonance (MR) thermally activated delayed fluorescence (MR-TADF) materials, categorized for the B/N and carbonyl/amine fragments, are now intensively and widely studied due to their color purity. However, the relationship between the MR molecular structure and full width at half maximum (FWHM) of the emission remains elusive. In order to probe the factor of determining the emission FWHM of the MR emitters, a series of relevant molecules were synthesized where the MR core acceptor moiety, phenylborane or acetophenone, is fixed, while the donor moiety is altered to adjust the charge transfer (CT) strength. These potential MR molecules provide sufficient photophysical data to shed light on the emission bandwidth influenced by CT strength. Meanwhile, OLEDs fabricated using all the studied compounds achieve maximum external quantum efficiencies (EQEmax) around 7.0–15.3% because of the TADF character induced by the host/guest interaction in the excited state. The results provide further understanding on the fundamentals of the MR emitters. [ABSTRACT FROM AUTHOR]

The development of near-infrared (NIR)-emitting phosphorescent emitters are still urgently needed for solution-processed organic light-emitting diodes (SP-OLEDs) with high efficiency, radiant emittance, and low cost. Herein, we designed and synthesized a new iridium complex, namely (tBuTPA–DBPz)2Ir(acac), with the rigid C^N coordinated core of dibenzo[a,c] phenazine (DBPz) and an amplifying peripheral shell of 4,4′-di(tert-butyl)-triphenylamine (tBuTPA) attached at its 3,6-positions. The influence of the rigid DBPz core and big tBuTPA shell on the photophysical, electrochemical and electroluminescent properties of (tBuTPA–DBPz)2Ir(acac) was primarily studied in comparison with the archetype (DBPz)2Ir(dpm). The NIR emission peaked at 714 nm with an outstanding external quantum efficiency of 12.25% and a recorded radiant emittance of 45 330 mW Sr−1 m−2 was observed in the (tBuTPA–DBPz)2Ir(acac)-doped devices at an optimized dopant ratio of 8 wt%. The EQE is 1.57 times that of (DBPz)2Ir(dpm)-doped devices. Moreover, this NIR light-emitting device contains an Ir(III) content as low as 0.68 wt% and exhibits a bright NIR emission at 714 nm with outstanding efficiency and radiant emittance. Our results indicate that the NIR-emitting OLEDs with high efficiency, radiant emittance and low cost should be realized by developing core–shell type Ir(III) complexes with a rigid C^N coordinate core and an amplifying shell. [ABSTRACT FROM AUTHOR]

An efficient blue thermally-activated delayed fluorescence (TADF) emitter is still a challenge in solution-processed organic light-emitting diodes (OLEDs). In this contribution, two asymmetric molecules, TTT-Ac and TTT-2Ac were synthesized and characterized, in which the tris(triazolo)triazine (TTT) fragment is used as the acceptor core and different numbers of acridine (Ac, one or two) units are considered as the donor unit. Both compounds display clear TADF character, concomitant with the emission between 420 and 450 nm in a doped PMMA film. Compared to TTT-2Ac, TTT-Ac shows blue-shifted emission due to its weaker intramolecular charge transfer effect. The solution-processed OLEDs achieve a maximum external quantum efficiency (EQEmax) of 9.26% and 8.10% with the emission peak at about 470 nm for TTT-Ac and TTT-2Ac, respectively. Furthermore, the TTT-Ac-based solution-processed OLED exhibits an EQEmax of 10.01% after optimization of the emitter thickness. This research focuses on the molecular structure–property relationship of TTT-based molecules, which enriches the TTT-based solution-processable sky-blue TADF emitter. [ABSTRACT FROM AUTHOR]

Two intermediate-sized acceptor–π–porphyrin–π–acceptor-type molecules MPor1 and MPor2 with panchromatic absorption profiles have been developed towards improving photovoltaic performance. The conjugation of terthiophenyl-benzodithiophene to the porphyrin center successfully fills the absorption gap between the Soret and Q bands of the conventional porphyrin molecules and leads to narrow optical bandgaps within 1.58–1.60 eV. The two molecules possess excellent light-harvesting property within the UV-visible-near-infrared region, and efficient hole-electron separation in the bulk heterojunction layer with PC71BM as the acceptor. Conventional solar cells based on the MPor1/PC71BM active layer shows an optimal performance with a power conversion efficiency of 8.59% and a short circle current of 14.91 mA cm−2. [ABSTRACT FROM AUTHOR]

It is crucial to develop high-efficiency simple-structure small molecular acceptors (SMAs) having a shortened synthetic route and lower cost. Herein, two simple SMAs, BDDTTIC and BDDTTIC-4F, with the A–D–A′–D–A architecture were primarily synthesized via a simple three-step route in high yields, based on the central acceptor (A′) unit of benzodithiophenedione (BDD), the spacing donor (D) unit of thienothiophene (TT) and the terminal acceptor (A) unit of dicyanomethylene indanone (IC) or its fluorinated analog (IC-4F). The influence of the molecular structure on the photophysical, electrochemical and photovoltaic properties was primarily studied. The results show that the fluorine-free BDDTTIC exhibits better solubility and higher LUMO energy levels (−3.81 eV) than the fluorinated BDDTTIC-4F. Moreover, the PM6:BDDTTIC based OSCs show better photovoltaic properties than the PM6:BDDTTIC-4F based OSCs by optimizing the polymer donor material, donor/acceptor ratio and 1-chloronaphthalene additive ratio. An increasing power conversion efficiency of 5.62% with a high open-circuit voltage of 0.95 V was obtained in the optimal PM6:BDDTTIC-based device, which is almost two times higher than that of the optimal PM6:BDDTTIC-4F-based device. This work provides a potential direction to further construct high-efficiency BDD-based SMAs. [ABSTRACT FROM AUTHOR]

A small molecule donor TiC12 with an asymmetric thieno[3,2-c]isochromene unit is incorporated into the PM6:Y6 system as the third component for constructing ternary organic solar cells (OSCs). It was found that TiC12 played an outstanding role in improvement of open-circuit voltage (Voc), short-circuit current (Jsc) and fill factor (FF) for the OSCs. The effects of TiC12 on the absorption, exciton dissociation, charge extraction, bimolecular recombination and morphology of the active layer are analyzed in detail. The synergetic improvement of Jsc, Voc and FF parameters is realized to generate an advanced power conversion efficiency (PCE) of 17.25% in the optimized PM6 : TiC12 : Y6 (0.9 : 0.1 : 1.2) ternary device. Furthermore, the Voc is increased in proportion to the added amount of TiC12 in the ternary devices due to reduced disorder and nonradiative energy loss, although the guest donor TiC12 exhibited a higher HOMO level than PM6. This study provides an effective and innovative approach to elevate Voc and thus PCE for ternary OSCs by introducing a guest small molecule donor with a higher HOMO level and better miscibility with the acceptor. [ABSTRACT FROM AUTHOR]

With the meteoric progress of near-infrared (NIR) emission materials for solution-processed polymer light-emitting diodes (PLEDs), exploring efficient NIR materials is still a key science issue. Herein, acceptor (A)–donor (D)–acceptor (A) rigid backbone 2,7-di(isoquinolin-1-yl)pyrene (BIQPy) as a cyclometalated ligand was treated with the anion of dipivaloyl methane (DPM) to afford a novel shoulder to shoulder-type binuclear platinum(II) complex, (BIQPy)[Pt(DPM)]2; the complex and its mononuclear analogue (BIQPy)Pt(DPM) were successfully strategically designed and synthesized. The photophysical, electrochemical and electroluminescent performances of complexes were primarily systematically studied. Upon introducing a second platinum(II) ion, the relevant binuclear platinum(II) complex displays notably red-shifted emission characteristics. Strong deep-red (DR) emission at 630 nm with a quantum efficiency (ΦPL) of 21.44% and a lifetime of 0.45 μs is obtained in (BIQPy)Pt(DPM) solution. Conversely, an outstandingly red-shifted NIR emission at 704 nm with a ΦPL of 16.94% and a lifetime of 0.39 μs is observed in (BIQPy)[Pt(DPM)]2 solution. Solution-processed PLEDs employing (BIQPy)Pt(DPM) as a dopant exhibit a stable electroluminescence (EL) emission of 630 nm and a shoulder at around 672 nm in the DR area, along with an efficient external quantum efficiency (EQE) of 8.84% and a brightness of 3328 cd m−2. Encouragingly, an NIR emission peak at 700 nm with an efficient EQE of 6.06% and a radiance of up to 24 259 mW Sr−1 m−2 was observed in (BIQPy)[Pt(DPM)]2-doped PLEDs. Results demonstrate that high-efficiency NIR-emitting binuclear platinum(II) complexes can be afforded by designing a shoulder to shoulder-type N^C–C^N tetradentate cyclometalating ligand with a fused rigid planar ligand. [ABSTRACT FROM AUTHOR]

Emissive gold(III) complexes of pincer 2,6-diphenylpyridines also bearing a phenylacetylide ligand have been modified at both the pincer and phenylacetylide to confer liquid crystalline properties, with most complexes showing a columnar hexagonal phase in the condensed phase. Solution NMR studies show a preferred orientation for self-association, consistent with structural parameters in the liquid crystal phase obtained by X-ray methods. While the pattern of substitution of the phenylacetylide has no discernible effect on the photophysics, when two alkoxy chains are attached to the pincer ligands, photoluminescence quantum yields (PLQY) of around 3% are found, whereas when four alkoxy chains are attached the PLQY increases significantly to 36%. Insight from computational chemistry indicated that the incorporation of the alkoxy donor groups raises the energy of the pincer-based HOMO−1 orbital, with a concomitant lowering of the LUMO ← HOMO−1 transition energy, consistent with an experimentally observed red shift. The gold complexes were fabricated into OLED devices using solution processing methods, being doped into the emissive layer at 5%, leading to external quantum efficiencies of up to 7.14%, values that compare well with those of related complexes in the literature. [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]

9,10-Dihydroacridine is a very popular donor unit for the construction of thermally activated delayed fluorescence (TADF) molecules due to its good electron-donating properties and potential for chemical modifications. However, the functionalization of the 2/7-positions of the acridine unit has rarely been explored. In this contribution, the novel donor moiety 9,9,9′9′-tetramethyl-9,9′10,10′-tetrahydro-2,10′-biacridine (BDMAc) was prepared via a one-pot C–H arylation procedure. Different acceptor fragments, diphenylsulfone (DPS), benzophenone (BPO) and 1,3,5-triazine (TRZ), were then introduced to synthesize three donor–acceptor molecules: DPS-BDMAc, BPO-BDMAc and TRZ-BDMAc. Single crystal X-ray diffraction and theoretical calculations show that these molecules possess twisted molecular geometries and small energy gaps between the singlet and triplet excited states. All molecules exhibit TADF properties with emission peaks between 480–600 nm in both solution and solid states, along with a high emission efficiency of 69–89% in the solid state. Solution-processed organic light-emitting diodes (OLEDs) based on these molecules were prepared with 25 wt% dopant concentration. Although the devices showed efficiency roll-off, a promising maximum EQE of ∼23% and a luminance of 7173 cd m−2 were obtained for the BPO-BDMAc-based device. This research demonstrates the potential of this novel acridine group for designing TADF molecules for efficient solution-processable OLEDs. [ABSTRACT FROM AUTHOR]

A novel bipolar NIR iridium(III) complex (CH3OTPA-BTz-Iq)2Ir(pic-OXD) with both a hole transporting (HT) triphenylamine (TPA) group and an electron transporting (ET) oxadiazole (OXD) group was designed and synthesized. It was observed that the incorporation of OXD and TPA into the ligand (CH3OTPA-BTz-Iq)2Ir(pic-OXD) improved the optophysical and electroluminescence performance in comparison with the parent iridium(III) complex (CH3OTPA-BTz-Iq)2Irpic. In (CH3OTPA-BTz-Iq)2Ir(pic-OXD)-based OLEDs, a maximum external quantum efficiency (EQEmax) of 1.15% at 716 nm was obtained, which is much superior than that of the (CH3OTPA-BTz-Iq)2Irpic-based OLEDs (0.41% at 723 nm). [ABSTRACT FROM AUTHOR]

Two types of asymmetric binuclear platinum(II) complexes (Pt-1 and Pt-3) bearing bridging ligands of 2-(2,4-difluorophenyl)-5-(pyridin-2-yl)pyridine and 2-(2,4-difluorophenyl)-4-(pyridin-2-yl)pyridine as well as their corresponding mononuclear counterparts (Pt-2, Pt-4, and Pt-5) were synthesized and characterized. Different chelating constructions of the second platinum(II) ions and the bridging ligands in Pt-1 and Pt-3 gave rise to two kinds of electron-transition pathway during their photophysical processes. The meta-/para-carbon of nitrogen on the center pyridyl segments set different levels of ligand field strength to the second platinum(II) ions, lowering their occupied d orbital to varying degrees. Pt-1 showed an enhanced spin–orbit coupling (SOC), caused by the additional metal component through direct orbital hybridization at higher states, where the fixed molecular skeleton induced by the additional metal–ligand bonding also helped to suppress molecular distortion in the excited state, ensuring a high quantum yield (Φ, 0.89 in toluene), which is among the best results in bimetallic complexes. While the second platinum(II) ion in Pt-3 seemed to make no contribution to the radiative transition, and only contributed to the HOMO, it provided a benefit by enlarging the conjugate system. Solution-processed organic lighting emitting devices (OLEDs) fabricated with the bimetallic Pt-1 emitter achieved superior efficiencies and up to 21% external quantum efficiency (EQE) in the Kelly-green region. [ABSTRACT FROM AUTHOR]

To systematically investigate the σ–π and p–π conjugation effects on photoluminescence (PL) and electroluminescence (EL) properties, and to obtain high-efficiency near-infrared (NIR)-emitting iridium(III) complexes, in this work, two rigid C^N ligands of dibenzo[a,c]phenazine (DBPz) derivatives, respectively, anchored by flexible side chains of n-octyl and n-octyloxy and their corresponding iridium(III) complexes of Ir-R and Ir-OR were designed and synthesized. Their photophysical and EL properties were systematically investigated. It is found that the σ–π and p–π conjugation effects can make both iridium(III) complexes exhibit a significantly red-shifted NIR emission with high photoluminescence quantum efficiency (PLQY) in comparison with their archetypal iridium complex without any side chains. More intense NIR emissions are achieved for Ir-R at 732 nm (PLQY: 24%) and Ir-OR at 775 nm (PLQY: 8%) in dichloromethane solution. Utilizing Ir-R as the phosphorescent dopant, the solution-processed organic light-emitting diodes (OLEDs) using CBP as the host and polymer light-emitting diodes (PLEDs) using PVK:OXD-7 as the cohost show outstanding EL performances. The highest external quantum efficiency (EQE) of 6.91% and a radiance of 26 100 mW sr−1 m−2 were obtained in the Ir-R based OLEDs with an emission peak at 730 nm, which are 4.7 and 2.2 times higher than those of the complex Ir-OR-based devices. This indicates that introducing σ–π conjugation effects induced by the anchored flexible n-octyl side chains in the rigid dibenzo[a,c]phenazine moiety is a better strategy for obtaining NIR-emitting iridium complexes for application in high-efficiency solution-processed devices. [ABSTRACT FROM AUTHOR]

In order to investigate the effects of the substitution position on the photovoltaic performance of donor polymers, two benzothiophene ring substituted benzo(1,2-b:4,5-b′)dithiophene (BDT)-based conjugated polymers (PBDTBTs-BDD and PBDTTBs-BDD) are designed and synthesized. The variation in the substitution position has small influences on the photophysical properties but has a great effect on the intramolecular π–π stack structure, charge transport and photovoltaic properties. PBDTBTs-BDD (with the 6-position of the benzothiophene substituent) exhibited a smaller π–π stacking distance of 3.67 Å compared to 4.11 Å seen for PBDTTBs-BDD (with the 2-position of the benzothiophene substituent). And the charge mobilities of PBDTBTs-BDD-based devices are higher and more balanced than those of PBDTTBs-BDD-based devices, which are highly beneficial for reducing recombination of free carriers and then lead to a higher short-circuit current density (JSC) and fill factor (FF) of devices. With ITIC or Y6 as non-fullerene acceptors, PBDTBTs-BDD-based devices exhibit power conversion efficiencies (PCE) of 7.76% and 12.07%, respectively, which are higher than those of PBDTTBs-BDD-based devices (5.04% and 5.81%). This work demonstrates that the photovoltaic properties of donor polymers can be highly tunable through slight modifications of their side chain structures. [ABSTRACT FROM AUTHOR]

An acceptor–donor–donor–acceptor (A–D–D–A)-type near-infrared non-fullerene small-molecule acceptor IDT2-DFIC with indacenodithiophene–indacenodithiophene (IDT2) as a donating core and 2-(5,6-difluoro-3-oxo-2,3-dihydro-1H-inden-1-ylidene)malononitrile (2FIC) as electron withdrawing end groups has been synthesized. Compared to A–D–A-type small-molecule acceptor IDIC-4F, IDT2-DFIC exhibits a low optical bandgap of 1.42 eV with strong absorption in the 450–874 nm region, and upshifted energy levels as an electron acceptor. Furthermore, the IDT2-DFIC-based devices exhibited higher and more balanced charge transport and smoother surface morphology. The power conversion efficiency (PCE) of the IDT2-DFIC-based devices is 10.06%, which is higher than that of the IDIC-4F-based devices (5.17%). Our work provides an efficient molecular design strategy to construct small molecule acceptors with near-infrared absorption. [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]

Deep-red/near-infrared (DR/NIR) OLEDs based on transition metal complexes have drawn much attention due to their potential applications in displays, bioimaging and photodynamic therapy. In this article, two novel iridium(III) complexes, (DBPz-11,12-DO)2Ir(acac) and (PPz-11,12-DO)2Ir(acac), were primarily designed and synthesized using highly rigid fused-heterocyclic phenazine derivatives as ligands. By tuning the benzo number in the phenazine, the iridium complexes exhibited significantly different emission characteristics. Strong NIR emission at 732 nm with a quantum efficiency of 13% and a lifetime of 0.60 μs was observed in the (PPz-11,12-DO)2Ir(acac) solution. In contrast, a remarkably blue-shifted DR emission at 685 nm with a quantum efficiency of 27% and a lifetime of 0.40 μs was exhibited in the (DBPz-11,12-DO)2Ir(acac) solution. As a result, both iridium complexes exhibited high-efficiency DR/NIR electroluminescence in their doped polymer light-emitting devices. The (PPz-11,12-DO)2Ir(acac) devices showed a maximum external quantum efficiency (EQE) of 4.14% with a radiance of up to 20 981 mW Sr−1 m−2, and the (DBPz-11,12-DO)2Ir(acac) devices afford an increased EQE of 7.04% with a radiance of 33 671 mW Sr−1 m−2. This strategy of using rigid fused-heterocyclic cyclometalated ligands has opened a new avenue for high-efficiency DR/NIR-emitting iridium complexes. [ABSTRACT FROM AUTHOR]

Four isomeric dinuclear platinum complexes of (C^N)2Pt2(μ-OXT)2 are synthesized and characterized with different C^N cyclometalating ligands and the same ancillary ligand of 5-(4-octylphenyl)-1,3,4-oxadiazole-2-thiol (μ-OXT). These isomeric C^N ligands are 1-naphthyl-1-isoquinoline (niq), 2-naphthyl-1-isoquinoline (2niq), 1-naphthyl-2-quinoline (nq) and 2-naphthyl-2-quinoline (2nq). The isomeric effect on the photophysical, electrochemical and electroluminescence properties of (C^N)2Pt2(μ-OXT)2 was systematically studied. It is found that the emissions were easy to tune from deep red to near infrared for (C^N)2Pt2(μ-OXT)2 by changing the C^N isomers. Furthermore, the complexes with 2-naphthyl presented better electroluminescence (EL) properties than the complexes with 1-naphthyl in these solution-processable polymeric light-emitting devices. In contrast to the (2nq)2Pt2(μ-OXT)2-doped devices displaying a deep-red emission peaked at 686 nm with an external quantum efficiency (EQE) of 3.21%, the (2niq)2Pt2(μ-OXT)2-doped devices exhibited a near-infrared emission peaked at 704 nm with a significantly increased EQE of 8.86% and a radiant emittance of 986 μW cm−2. Our research provides an efficient strategy to tune emission from deep red to near infrared by a simple isomeric engineering of dinuclear platinum(II) complexes. [ABSTRACT FROM AUTHOR]

Non-fullerene organic solar cells (OSCs) have attracted significant attention recently due to their tremendous advances in power conversion efficiency (PCE). It has been found that most non-fullerenes are small molecule acceptors (SMAs) bearing electron-rich cores of polycyclic arenes. However, these polycyclic arenes have a high synthetic cost. Here, a novel strategy is proposed to construct SMAs using simple and weakly electron-deficient thiazolothiazole (TTz) as the core. Two simple-structured SMAs of TTz1 and TTz2 with an A(π–A′–A′′)2 framework are designed and synthesized for potential applications in OSCs, in which benzothiadiazole and malononitrile derivatives are employed as a dual electron-accepting (A′–A′′) arm. Their optical, electrochemical and photovoltaic performances are systematically investigated. We find that both TTz1 and TTz2 exhibit decreased LUMO and increased HOMO energy levels in comparison to the prototypical small molecules TT0 and TTz0 bearing a single electron-accepting (A′′) terminal end. Medium optical bandgap of about 1.60 eV and satisfactory energy levels are obtained for both molecules TTz1 and TTz2 with more balanced carrier mobility by introducing a novel TTz core and tuning the A′–A′′ arm. The highest PCE value of 8.77% is recorded in TTz1-based OSCs blended with the common electron-donating material J71, which is the highest efficiency among OSCs using simple-structured SMAs as non-fullerenes to date. This study reveals great potential to construct high-efficiency and simple-structured SMAs using a weakly electron-deficient TTz core instead of an electron-donating polycyclic arene core. [ABSTRACT FROM AUTHOR]

Metal atoms with excellent magnetic, electrical and optical properties that are integrated into liquid crystal molecules – metallomesogens – have attracted much attention from chemists, physicists and engineers and many materials based on e.g. Ag, Pt, Pd, Ir, Ni, Cu and lanthanide ions have been reported. Though several reviews and books have been published on metallomesogens, few refer to their photophysical properties. Additionally, metallomesogens with good emission properties in solution or in neat film are still scarce. Owing to the 100% theoretical internal quantum efficiency, phosphorescent liquid-crystalline materials were developed recently. Here, a brief overview of recent research on such materials based on platinum and iridium complexes including their molecular design and structure–property relationships is reported. It is hoped that this review will stimulate further development of luminescent metallomesogens. [ABSTRACT FROM AUTHOR]

Linear small molecules have been proved to be promising donor materials for high performance small molecular solar cells (SMSCs). In this paper, a series of narrow-band gap, π-conjugated small molecules (SMs) with a D(A–Ar)2 linear framework, denoted as FBT(PyDPP-T)2, FBT(IID-T)2 and FBT(TDPP-T)2, based on fluorinated 2,2′-bithiophene (FBT) as an electron-donating (D) central core, pyridine-flanked diketopyrrolopyrrole (PyDPP), isoindigo (IID) or thiophene-flanked diketopyrrolopyrrole (TDPP) as electron-accepting (A) units, and 2-octylthiophene (Ar) units as end-capping units, have been designed and synthesized for application as donor materials in solution-processed SM organic solar cells (OSCs). The impacts of different acceptor units and fluorinated central cores on bulk properties, such as the optoelectronic properties, carrier mobility, the HOMO/LUMO energy level, and the morphologies of blend films, as well as optimization on device performance via appropriate solvent vapor annealing (SVA) are systematically investigated. The as-cast devices based on FBT(PyDPP-T)2, FBT(IID-T)2 and FBT(TDPP-T)2 exhibit PCEs of 5.04%, 5.68% and 6.86%, respectively. Encouragingly, after a SVA treatment with carbon disulfide (CS2) for 20 s, an impressively improved power conversion efficiency (PCE) from 6.86% to 9.00% with an increase of 35% was obtained in the FBT(TDPP-T)2/PC71BM (w/w, 1 : 1) based cells due to an enhanced short circuit current density (Jsc) of 16.14 mA cm−2 and fill factor (FF) of 73.52%, which is among the highest reported for D(A–Ar)2-type SM-based solar cells with a PCE up to 9.0% so far. Our research results reported here clearly demonstrate that highly efficient SM-OSCs can be obtained via rational design of their molecular structure and optimization of the phase-separated morphology through an appropriate solvent-vapor annealing process. [ABSTRACT FROM AUTHOR]

Two new zig-zag type di- and mono-nuclear platinum(ii) complexes of (BuPh-BDIQ)Pt2(dpm)2 and (BuPh-BDIQ)Ptdpm were synthesized and characterized by using a zig-zag type cyclometalating ligand 3,10-di(tert-butyl)-5,12-bis(4-(tert-butyl)phenyl)-benzodiisoquinoline (BuPh-BDIQ). Their single-crystal structures, and photophysical, electrochemical and electroluminescent properties were primarily investigated. Compared with (BuPh-BDIQ)Ptdpm, (BuPh-BDIQ)Pt2(dpm)2 exhibited a significantly increased photoluminescent efficiency of 3.64% and a red-shifted near-infrared (NIR) emission peak at 718 nm owing to its enhanced rigid planar structure in a nitrogen atmosphere. As a result, only (BuPh-BDIQ)Pt2(dpm)2 presented NIR electroluminescent emission in a doped polymeric light-emitting diode. The highest external quantum efficiency of 0.97% and a radiant intensity of 146 μW cm−2 were observed for the device at 2 wt% dopant concentration, which is higher than the values of previous NIR-emitting di-nuclear platinum complexes constructed with cyclometalated ligands. Furthermore, efficiency roll-off was efficiently inhibited. This indicates that high-efficiency NIR-emitting di-nuclear platinum complexes can be obtained by designing a zig-zag type C^N–C^N tetradentate cyclometalating ligand with a big rigid planar saw band. [ABSTRACT FROM AUTHOR]

Isomeric TF1 and TF2 with highly fused thiophene cores were designed and synthesized here, in which a highly planar molecular structure was obtained for TF1 with the face-to-face sulfur atoms in the lateral region and a twisted molecular backbone was observed for TF2 with the back-to-back sulfur atoms. It is worth noting that different intermolecular interactions dominated in TF1 and TF2 caused by their isomeric thiophene cores, in which strong π–π stacking was achieved for TF1, whereas sulphur-involved nonbonding intermolecular interactions dominated in TF2, leading to the different fluorescence behaviors and also the altered liquid crystalline phases. Finally, typical P-type charge transport behaviors were achieved in both TF1- and TF2-based solution-processed OFETs. Also owing to the much ordered molecular packing in TF1, a higher charge carrier mobility of 3.7 × 10−3 cm2 V−1 s−1 was achieved for TF1-based OFETs compared to TF2-based OFETs. [ABSTRACT FROM AUTHOR]

Directly polarized organic light emitting diodes (OLEDs) have the potential to significantly improve the efficiency and reduce the cost of liquid-crystal displays (LCDs) among other applications. However, fluorescent liquid crystals are currently used to achieve this, while phosphorescent emitters would further improve efficiency. To this end, the metallomesogens based on ionic iridium complexes bearing different aliphatic chains substituent, named 7a and 7b, were designed and prepared in this contribution. Both iridium complexes showed smectic mesophase evidenced by differential scanning calorimetry, polarized optical microscopy and X-ray diffraction. Deep-red emission was observed for the iridium complexes in solution and solid state, and complex 7a clearly presented aggregation-induced emission (AIE) behavior in THF–water solvent mixture. Non-doped polarized OLEDs employing complex 7a or 7b as emitter were fabricated and direct linearly polarized electroluminescence with a polarization ratio of 4 was achieved, which is the highest ratio reported for metallomesogens-based phosphorescent OLEDs. Importantly, the choice of linker between the core complex and mesogenic pendent groups is key to achieve distinctive polarization of electroluminescence and AIE. These results are a first step towards the development phosphorescent OLEDs able to efficiently produce polarized electroluminescence. [ABSTRACT FROM AUTHOR]

Electroluminescence performance of perovskite light-emitting diodes (PeLEDs) is extremely dependent on the morphology of the perovskite films, which is influenced by the processing method. Herein, we report an effective approach for the preparation of a high-quality perovskite film with perfect performance for PeLEDs via a solution process at room temperature. On the one hand, CH3NH3PbBr3 (MAPbBr3) precursor solution was blended with a traditional polymeric host PVK [poly(vinylcarbazole)] to obtain smooth and uniform perovskite films. On the other hand, the perovskite films could be further improved through crystal modification to obtain a more uniform morphology and smaller grain sizes. Our research also demonstrated the feasibility of preparing high-performance solution-processed PeLEDs by blending small molecule hole-transport materials (HTMs) with polymer HTMs (widely used in OLEDs as hole-transport layers (HTLs)). Efficient green PeLEDs with a current efficiency (CE) of 6.7 cd A−1, external quantum efficiency (EQE) of 1.88%, and low turn-on voltage of 2.9 V were achieved; this indicates that the effective solution process used to improve the morphology of the perovskite films as well as carrier injection has great potential for the development of high-performance PeLEDs. [ABSTRACT FROM AUTHOR]

In order to seek the balance point between liquid crystallinity and high efficiency emission, two novel aggregation-induced emission-based (AIE) liquid crystal materials of TPE-PBN and TPE-2PBN, which contain a tetraphenylethene derivative as the emission core and a 4-cynobiphenyl moiety as the mesogenic unit, were designed and prepared. Both simple molecules showed a mesophase at high temperature as evidenced by polarised optical microscopy (POM), differential scanning calorimetry (DSC) and temperature-dependent X-ray diffraction (XRD). Simultaneously, TPE-PBN and TPE-2PBN presented clear AIE characteristics in the blueish-green region and achieved a high emission quantum efficiency of 71% and 83% in the solid state, respectively. Due to the self-assembly properties of thermotropic liquid crystals, both compounds showed higher hole mobilities in the annealed films than in pristine films. Employing TPE-PBN and TPE-2PBN as the emitting materials, both non-doped devices and doped devices were fabricated. The TPE-PBN-based doped OLEDs showed a better device performance with an external quantum efficiency (EQE) of 4.1% which is among the highest EQEs of blue AIE fluorescent OLEDs. [ABSTRACT FROM AUTHOR]

In aiming to build novel wide band-gap high-performance photovoltaic donor materials, a vertical benzo[1,2-b:4,5-b′]dithiophene-2,6-dicarboxylate (V-BDTC) with a weak electron-withdrawing character was primarily developed. And its wide band-gap (WBG) copolymers PV-BDTC1 and PV-BDTC2 were designed and synthesized, which contain a traditional electron-donating unit of 4,8-disubstituted benzo[1,2-b:4,5-b′] dithiophene (BDT) derivative with diethylhexyloxy for the former and diethylhexylthiophenyl for the latter. It is found that the weak electron-withdrawing V-BDTC unit endows its copolymers with a WBG up to 2.09 eV and a deep HOMO energy level of ∼5.67 eV. Furthermore, PV-BDTC2 exhibits much better photovoltaic properties than PV-BDTC1 in the solution-processing polymer solar cells (PSCs) with a higher open-circuit voltage (Voc) of 1.03 V and an increased power conversion efficiency (PCE) of 7.49%. To the best of our knowledge, this PCE value is the highest level recorded for copolymers with a WBG over 2.0 eV in the PSCs to date, along with a remarkable Voc over 1.0 V. This work provides a feasible strategy to develop a novel promising electron-withdrawing building block and its high-performance WBG copolymers based on the BDT unit. [ABSTRACT FROM AUTHOR]

To control excimer/aggregation emission and achieve a single active emitter of aggregation for controllable white polymer light-emitting devices (PLEDs), two star-shaped dinuclear platinum(ii) complexes of C6DBCzC6-DFPt(pic) and DPy(TPA)-C6DBCzC6-DFPt(pic) were synthesized and characterized, in which DBCz is a 3,6-diphenyl-carbazole bridged core, C6 is an unconjugated dioxyhexyloxy linkage, DPy(TPA) is (4,4′-di(pyren-1-yl)triphenylamine), a deep blue-emitting fluorescent chromophore, and DPtF(pic) is a dinuclear platinum(ii) [(4,6-difluorophenyl)-pyridinato-N,C2′](picolinate) blue-emitting phosphorescent chromophore. Compared to its parent complex C6DBCzC6-DFPt(pic), DPy(TPA)-C6DBCzC6-DFPt(pic) showed a lower lying highest occupied molecular energy level (HOMO) and lowest unoccupied molecular energy level (LUMO). Under a current of 2.5 mA, near-white emission was obtained in the DPy(TPA)-C6DBCzC6-DFPt(pic)-doped devices at dopant concentrations from 4 wt% to 10 wt%. However, green-yellow emission was obtained in the C6DBCzC6-DFPt(pic)-doped devices with the same device configuration using a blend of polyvinylcarbazole (PVK) and 2-(4-biphenyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole (PBD) as a host matrix, respectively. This indicates that incorporating a deep blue fluorescent chromophore into a green-yellow emitting dinuclear platinum(ii) complex is an available way to control aggregation/excimer emissions and get white-emitting PLEDs with a single dopant. [ABSTRACT FROM AUTHOR]

Two novel dinuclear platinum complexes of (2niq)2Pt2(μ-C8PhOXT)2 and (piq)2Pt2(μ-PhOXT)2 were synthesized and characterized, where 2niq is 2-naphthyl-isoquinolinate, piq is 1-pheny-isoquinolinate, and μ-C8PhOXT and μ-PhOXT are anions of 5-(4-octylphenyl)-1,3,4-oxadiazole-2-thiol and 5-phenyl-1,3,4-oxadiazole-2-thiol, respectively. The Pt–Pt bond was confirmed by the (piq)2Pt2(μ-PhOXT)2 single crystal. A high-efficiency NIR electroluminescence peak at about 704 nm was observed for this (2niq)2Pt2(μ-C8PhOXT)2 in the solution-processed PLEDs with a notable external quantum efficiency (EQE) of 8.86% and an irradiate of 986 μW cm−2 at 9 wt% dopant concentration. Moreover, the efficiency roll-off was efficiently restrained, with an EQE of 5.22% at a current density of 100 mA cm−2 and 8.47% at 12 wt% dopant concentration. [ABSTRACT FROM AUTHOR]

Utilizing indacenodithiophene (D) and quinoxaline (A) building blocks, novel D–A–π–A type regular terpolymers of PIDT-DTQ-TT were designed with a conjugated π spacer of thieno[3,2-b]thiophene unit in the polymer backbone. In contrast to PIDT-DTQ with the thiophene unit as the spacer, PIDT-DTQ-TT displayed a much broader absorption with suitable HOMO energy levels and high charge carrier mobility. Also an enhanced Jsc of 12.43 mA cm−2 and a Voc of 0.83 V comparable to that of PIDT-DTQ-based devices were observed in PIDT-DTQ-TT-based solar cells, indicating that the balance between Jsc and Voc in devices can be achieved when the spacer in the polymer backbone was altered individually in D–A–π–A type regular terpolymers. Finally, a maximum power conversion efficiency value of 6.63% was achieved without any post-treatment in solar cells. Our results here demonstrate that tuning the conjugated spacers in D–A–π–A type regular terpolymers individually could be an efficient method to balance the trade-off between Jsc and Voc, leading to an enhanced photovoltaic performance in solar cells. [ABSTRACT FROM AUTHOR]