以昇陳

In an ordinal exciplex-based organic light-emitting diode (OLED), injected holes and electrons immediately recombine to emit light. Meanwhile, an organic long-persistent luminescent (OLPL) system can store holes and electrons for a long time and exhibit luminescence by recombination. By optimizing the light-emitting layer of the exciplex-based OLED, OLPL from an OLED is achieved.

Abstract

Organic long-persistent luminescent systems (OLPLs) exhibiting long-lasting emission after photoexcitation consist of organic electron donors and acceptors, that are widely used in organic light-emitting diodes (OLEDs). Although OLPLs and OLEDs include very similar excitonic processes, long-lasting emission has never been observed in OLEDs. This study confirms the presence of long-persistent luminescence (LPL) under electrical excitation.

In article number 2007177, Feng Liu and co‐workers report the fabrication of ternary organic solar cells, achieving a significant J _SC boost, by virtue of their optimized crystalline feature, with the formation of eutectic crystalline fibrils. The optimal morphology suppresses energetic disorder and nongeminate recombination, and increases charge transfer and transport, yielding a high efficiency of 17.84% with significant current amplification.

Nature Energy, Published online: 10 May 2021; doi:10.1038/s41560-021-00820-x

An efficient polythiophene-based organic solar cell (OSC) is demonstrated based on a fluorinated polythiophene donor with deep highest occupied molecular orbital (HOMO) level and appropriate miscibility with the acceptor. With further interfacial modification by a fullerene self-assembled monolayer, a record power conversion efficiency (PCE) of 13.65% for polythiophene-based OSCs is achieved with the device processed from nonhalogenated solvent.

Abstract

Benefiting from low cost and simple synthesis, polythiophene (PT) derivatives are one of the most popular donor materials for organic solar cells (OSCs). However, polythiophene-based OSCs still suffer from inferior power conversion efficiency (PCE) than those based on donor–acceptor (D–A)-type conjugated polymers. Herein, a fluorinated polythiophene derivative, namely P4T2F-HD, is introduced to modulate the miscibility and morphology of the bulk heterojunction (BHJ)-active layer, leading to a significant improvement of the OSC performance. The Flory–Huggins interaction parameters calculated from the surface energy and differential scanning calorimetry results suggest that P4T2F-HD shows moderate miscibility with the popular nonfullerene acceptor Y6-BO (2,2′-((2Z,2′Z)-((12,13-bis(2-butyloctyl)-3,9-diundecyl-12,13-dihydro-[1,2,5]thiadiazolo[3,4-e]thieno[2′,3′:4′,5′]thieno[2′,3′:4,5]pyrrolo[3,2-g]thieno[2′,3′:4,5]thieno[3,2-b]indole-2,10-diyl)bis(methanylylidene))bis(5,6-difluoro-3-oxo-2,3-dihydro-1H-indene-2,1-diylidene))dimalononitrile), while poly(3-hexylthiophene) (P3HT) is very miscible with Y6-BO. As a result, the P4T2F-HD case forms desired nanoscale phase separation in the BHJ film while the P3HT case forms a completely mixed BHJ film, as revealed by transmission electron microscopy (TEM) and grazing-incidence wide-angle X-ray scattering (GIWAXS). By optimizing the cathode interface and the morphology of the P4T2F-HD:Y6-BO films processed from nonhalogenated solvents, a new record PCE of 13.65% for polythiophene-based OSCs is demonstrated. This work highlights the importance of controlling D/A interactions for achieving desired morphology and also demonstrates a promising OSC system for potential cost-effective organic photovoltaics.

The novel authentic photonic transistor memory based on the aggregation-induced emission (AIE)-polymer electrets demonstrates ultrafast photoresponse ability with versatile memory behaviors. The mechanism of photoinduced memory behaviors is comprehensively elucidated, and the roles of the semiconductor and photoresponsive electrets are confirmed by different optical analyses. Moreover, the molecular design concept of AIE-polymer structures can facilitate diverse storage demands.

Abstract

Organic photonic memory, featuring a variety of glamorously light-driven characteristics, is rapidly growing into an indispensable building block for next-generation optical communication systems. However, the ambiguity of their operating mechanism associated with the limitation of photoadaptive materials as an electronics promoter results in the slow development of photonic transistor-based devices. In this study, the conjugated polymers composed of donor–acceptor motifs with typical aggregation-induced emission (AIE) behaviors are designed and successfully discover high-performance photoprogrammable memory. Moreover, the mechanism of photoboosted recording behavior, attributed to the recombination of the formed interlayer excitons right after simultaneous excitation without applying vertical and parallel electric-field at the interface in-between active semiconductor and AIE polymers, is cautiously corroborated by steady-state PL and pulse PL measurements. The AIE-polymer memory devices perform ultrafast photoresponse time of 0.1 ms, an outstanding current switch ratio up to 10⁶, and retention stability over 40 000 s without significant dissipation. Furthermore, photoresponsive AIE-polymer electrets not only modulate the memory performance through the emission wavelength but easily switch storage behavior of nonvolatile memory from flash to WORM by adjusting the torsion-angle through the motif of the donor and acceptor moieties. These findings open an avenue for designing conjugated polymer electret for ultrafast optical storage devices.

A novel polymer acceptor PY2F-T with difluoro-monobromo end groups on monomer sub-units is synthesized, exhibiting extended absorption and stronger crystallinity compared to its non-fluorinated counterpart (PY-T). When employed in all-polymer solar cells, the PY2F-T based device yields an outstanding efficiency of 15.22% and retains a decent performance of 13.05% when processed under ambient conditions with an eco-friendly solvent (o-xylene, no additive).

Abstract

In this paper, a difluoro-monobromo end group is designed and synthesized, which is then used to construct a novel polymer acceptor (named PY2F-T) yielding high-performance all-polymer solar cells with 15.22% efficiency. The fluorination strategy can increase the intramolecular charge transfer and interchain packing of the previous PY-T based acceptor, and significantly improve photon harvesting and charge mobility of the resulting polymer acceptor. In addition, detailed morphology investigations reveal that the PY2F-T-based blend shows smaller domain spacing and higher domain purity, which significantly suppress charge recombination as supported by time-resolved techniques. These polymer properties enable simultaneously enhanced J _SC and FF of the PY2F-T-based devices, eventually delivering device efficiencies of over 15%, significantly outperforming that of the devices based on the non-fluorinated PY-T polymer (13%). More importantly, the PY2F-T-based active layers can be processed under ambient conditions and still achieve a 14.37% efficiency. They can also be processed using non-halogenated solvent o-xylene (no additive) and yield a decent performance of 13.05%. This work demonstrates the success of the fluorination strategy in the design of high-performance polymer acceptors, which provide guidelines for developing new all-PSCs with better efficiencies and stabilities for commercial applications.

External thermally activated delayed fluorescence (TADF) enhancement by exciplex matrixes is investigated with time-resolved photoluminescence and electroluminescence spectroscopies, which indicates reverse intersystem crossing and charge pre-separation provided by exciplex matrixes for TADF enhancement and quenching suppression. The unitary reverse intersystem crossing efficiency and dramatically reduced singlet and triplet nonradiative rate constants of CDBP:2DBSOSPO support its yellow TADF diodes with a record power efficiency of 114.9 lm W⁻¹.

Abstract

The understanding of the external enhancement effects from host matrixes on thermally activated delayed fluorescence (TADF) emitters is crucial but incomprehensive at present. Herein, a series of phosphine oxide (PO) acceptors mDBSOSPO (m = 2, 3, and 4, corresponding to PO substitution position) and 4,4'-bis(9-carbazolyl)-2,2'-dimethylbiphenyl (CDBP) as donor is used to construct CDBP:mDBSOSPO exciplex matrixes with typical TADF behaviors. After doped with a conventional yellow TADF emitter 4CzTPNBu, the exciplex matrixes dramatically elevate the reverse intersystem crossing (RISC) efficiencies up to 99%, effectively reduce triplet nonradiative rate constant, and tenfold increase singlet radiative/nonradiative ratio beyond 30 in the case of CDBP:2DBSOSPO:3% 4CzTPNBu. The time-resolved photoluminescence and electroluminescence (EL) spectra demonstrate that in contrast to single-molecular hosts, besides the additional RISC channel for TADF facilitation, the exciplexes support the charge preseparation for the step-by-step charge transfer-based energy transfer featuring effective quenching suppression. These external enhancement effects of the exciplex matrixes lead to the state-of-the-art EL performances of their yellow TADF diodes, including the recording power and quantum efficiencies of 114.9 lm W⁻¹ and 30.3% to date.

A new wide-bandgap conjugated polymer, PBQx-TCl, exhibits 18% efficiency for outdoor application and 28.5% efficiency for indoor application. Simultaneously, the PBQx-TCl-based device also shows light-emitting function with broad emission ranges from 630 to 1000 nm and moderate external quantum efficiency approaching 0.2%.

Abstract

Exploring the intriguing bifunctional nature of organic semiconductors and investigating the feasibility of fabricating bifunctional devices are of great significance in realizing various applications with one device. Here, the design of a new wide-bandgap polymer named PBQx-TCl (optical bandgap of 2.05 eV) is reported, and its applications in photovoltaic and light-emitting devices are studied. By fabricating devices with nonfullerene acceptors BTA3 and BTP-eC9, it is shown that the devices exhibit a high power conversion efficiency (PCE) of 18.0% under air mass 1.5G illumination conditions and an outstanding PCE of 28.5% for a 1 cm² device and 26.0% for a 10 cm² device under illumination from a 1000 lux light-emitting diode. In addition, the PBQx-TCl:BTA3-based device also demonstrates a moderate organic light-emitting diode performance with an electroluminescence external quantum efficiency approaching 0.2% and a broad emission range of 630–1000 nm. These results suggest that the polymer PBQx-TCl-based devices exhibit outstanding photovoltaic performance and potential light-emitting functions.

Integrated surgery and phototheranostics employing nanoparticles based on a near-infrared aggregation-induced emission luminogen (AIEgen) for image-guided synergistic tumor therapy are explored to overcome respective limitations and realize maximized therapeutic outcomes and minimized recurrences. Moreover, the combined treatment of AIEgen-nanoparticle-mediated phototheranostics and programmed death-ligand 1 antibody significantly induces tumor elimination by enhancing the effect of immunotherapy.

Abstract

Multimodal therapy is attracting increasing attention to improve tumor treatment efficacy, but generally requires various complicated ingredients combined within one theranostic system to achieve multiple functions. Herein, a multifunctional theranostic nanoplatform based on a single aggregation-induced-emission luminogen (AIEgen), DDTB, is designed to integrate near-infrared (NIR) fluorescence, photothermal, photodynamic, and immunological effects. Intravenously injected AIEgen-based nanoparticles can efficiently accumulate in tumors with NIR fluorescence to provide preoperative diagnosis. Most of the tumors are excised under intraoperative fluorescence navigation, whereafter, some microscopic residual tumors are completely ablated by photodynamic and photothermal therapies for maximally killing the tumor cells and tissues. Up to 90% of the survival rate can be achieved by this synergistic image-guided surgery and photodynamic and photothermal therapies. Importantly, the nanoparticles-mediated photothermal/photodynamic therapy plus programmed death-ligand 1 antibody significantly induce tumor elimination by enhancing the effect of immunotherapy. This theranostic strategy on the basis of a single AIEgen significantly improves the survival of cancer mice with maximized therapeutic outcomes, and holds great promise for clinical cancer treatment.

Two D–A copolymers, PBQ5 and PBQ6, are designed and synthesized based on difluoroquinoxaline (DFQ) units with different side chains. The organic solar cell (OSC) based on PBQ6 as donor and Y6 as acceptor achieves a high power conversion efficiency of 17.62%, which is one of the highest efficiencies for binary OSCs with a polymer donor and Y6 acceptor.

Abstract

Side-chain engineering has been an effective strategy in tuning electronic energy levels, intermolecular interaction, and aggregation morphology of organic photovoltaic materials, which is very important for improving the power conversion efficiency (PCE) of organic solar cells (OSCs). In this work, two D–A copolymers, PBQ5 and PBQ6, are designed and synthesized based on bithienyl-benzodithiophene (BDTT) as the donor (D) unit, difluoroquinoxaline (DFQ) with different side chains as the acceptor (A) unit, and thiophene as the π-bridges. PBQ6 with two alkyl-substituted fluorothiophene side chains on the DFQ units possesses redshifted absorption, stronger intermolecular interaction, and higher hole mobility than PBQ5 with two alkyl side chains on the DFQ units. The blend film of the PBQ6 donor with the Y6 acceptor shows higher and balanced hole/electron mobilities, less charge carrier recombination, and more favorable aggregation morphology. Therefore, the OSC based on PBQ6:Y6 achieves a PCE as high as 17.62% with a high fill factor of 77.91%, which is significantly higher than the PCE (15.55%) of the PBQ5:Y6-based OSC. The PCE of 17.62% is by far one of the highest efficiencies for the binary OSCs with polymer donor and Y6 acceptor.

Two pairs of circularly polarized multiple resonance thermally activated delayed fluorescence (CP-MR-TADF) enantiomers are developed by combining the merits of circularly polarized luminescence (CPL) and MR-TADF. This is the first example of a highly efficient organic light-emitting diode (OLED) that exhibits circularly polarized electroluminescence signal, narrowband emission, and TADF concurrently.

Abstract

Purely organic fluorescent materials that concurrently exhibit high efficiency, narrowband emission, and circularly polarized luminescence (CPL) remain an unaddressed issue despite their promising applications in wide color gamut- and 3D-display. Herein, the CPL optical property and multiple resonance (MR) effect induced thermally activated delayed fluorescence (MR-TADF) emission are integrated with high color purity and luminous efficiency together. Two pairs of highly efficient green CP-MR-TADF enantiomers, namely, (R/S)-OBN-2CN-BN and (R/S)-OBN-4CN-BN, are developed. The enantiomer-based organic light-emitting diodes (OLEDs) exhibit pure green emission with narrow full-width at half-maximums (FWHMs) of 30 and 33 nm, high maximum external quantum efficiencies (EQEs) of 29.4% and 24.5%, and clear circularly polarized electroluminescence (CPEL) signals with electroluminescence dissymmetry factors (g _EL) of +1.43 × 10⁻³/−1.27 × 10⁻³ and +4.60 × 10⁻⁴/−4.76 × 10⁻⁴, respectively. This is the first example of a highly efficient OLED that exhibits CPEL signal, narrowband emission, and TADF concurrently.

A nanotheranostic agent, which can realize two-stage programmed size changes, is developed for enhanced magnetic resonance imaging (MRI)-guided chemo/photodynamic combination therapy. Once the nano-sized agents reach the acidic tumor microenvironment, large aggregates will be formed for enhanced MRI. After their theranostic functionalities exhaust, large-sized aggregates will be transformed into monodisperse small-sized particles for fast elimination.

Abstract

An ideal nanotheranostic agent should be able to achieve efficient tumor accumulation, retention, and fast elimination after its theranostic functions exhausts. However, there is an irreconcilable contradiction on optimum sizes for effective tumor retention and fast elimination. Herein, a programmed size-changeable nanotheranostic agent based on polyprodrug-modified iron oxide nanoparticles (IONPs) and aggregation-induced emission photosensitizer is developed for enhanced magnetic resonance imaging (MRI)-guided chemo/photodynamic combination therapy. The nano-sized theranostic agents with an initial diameter of about 90 nm can accumulate in tumor tissue through passive targeting. In the acidic tumor microenvironment, large aggregates of IONPs are formed, realizing enhanced tumor retention and MR signal enhancement. Under the guidance of MRI, light irradiation is applied to the tumor site for triggering the generation of reactive oxygen species and drug release. Moreover, after chemo/photodynamic combination therapy, the large-sized aggregates are re-dispersed into small-sized IONPs for fast elimination, reducing the risk of toxicity caused by long-term retention. Therefore, this study provides a promising size-changeable strategy for the development of nanotheranostic agents.

Zwitterion-functionalized polymers are synthsized with a record-high breakdown strength of 1300 MV m⁻¹, energy density above 35 J cm⁻³, and charge–discharge efficiency of >90%, taking advantage of the covalent-bonding-restricted ion polarization and the charge trapping of the ion cluster phase.

Abstract

Polymer dielectrics are highly desirable in capacitor applications due to their low cost, high breakdown strength, and unique self-healing capability. However, existing polymer dielectrics suffer from either a low energy density or a high dielectric loss, thereby hindering the development of compact, efficient, and reliable power electronics. Here, a novel type of polymer dielectrics simultaneously exhibiting an extraordinarily high recoverable energy density of 35 J cm⁻³ and a low dielectric loss is reported. It is synthesized by grafting zwitterions onto the short side chains of a poly(4-methyl-1-pentene) (PMP)-based copolymer, which increases its dielectric constant from ≈2.2 to ≈5.2 and significantly enhances its breakdown strength from ≈700 MV m⁻¹ to ≈1300 MV m⁻¹ while maintaining its low dielectric loss of <0.002 and high charge–discharge efficiency of >90%. Based on a combination of the phase-field method description of mesoscale structures, Maxwell equations, and theoretical analysis, it is demonstrated that the outstanding combination of high energy density and low dielectric loss of zwitterions-grafted copolymers is attributed to the covalent-bonding restricted ion polarization and the strong charge trapping by the zwitterions. This work represents a new strategy in polymer dielectrics for achieving simultaneous high energy density and low dielectric loss.

A deep-red TADF emitter p CNQ–TPA for UHD display was demonstrated, which realized the desired chromaticity matching rec.2020 standard and the record external quantum efficiency beyond 30 %. It is showed that its quasi-planar structure not only improves horizontal ratio of emitting dipole orientation for out-coupling enhancement, but also balances the intra- and inter-molecular charge transfer for radiation facilitation and quenching suppression.

Abstract

Herein, we report a deep-red TADF emitter p CNQ–TPA, composed of quinoxaline-5,8-dicarbonitrile (pCNQ) acceptor and triphenylamine (TPA) donor. p CNQ–TPA supported its OLED with desired CIE coordinates of (0.69, 0.31) and the record maximum external quantum efficiency of 30.3 %, which is the best red TADF diode with Rec.2020 gamut for UHDTV. It is showed that through tuning p CNQ–TPA doping concentration, intra- and inter-molecular charge transfer are balanced to synchronously improve emission color saturation and TADF radiation, and remedy aggregation-induced quenching, rendering photoluminescence quantum yield (PLQY) reaching 90 % for deep-red emission peaked at ≈690 nm. Quasi-planar structure further endows p CNQ–TPA with an improved horizontal ratio of emitting dipole orientation, which increases light out-coupling ratio to 0.34 for achieving the state-of-the-art device efficiencies.

Based on the synergistic effect of the higher dielectric property of non-fullerene acceptors and corresponding photoactive films and the energy transfer from donor to acceptor on charge separation of selected non-fullerene-based photovoltaic devices, these results well interpret the high device performance with a tiny driving force, and the intrinsic physical working mechanism on non-fullerene-based photovoltaic devices is proposed.

Abstract

In non-fullerene-based photovoltaic devices, it is unclear how excitons efficiently dissociate into charge carriers under small driving force. Here, we developed a modified method to estimate dielectric constants of PM6 donor and non-fullerene acceptors. Surprisingly, most non-fullerene acceptors and blend films showed higher dielectric constants. Moreover, they exhibited larger dielectric constants differences at the optical frequency. These results are likely bound to reduced exciton binding energy and bimolecular recombination. Besides, the overlap between the emission spectrum of donor and absorption spectra of non-fullerene acceptors allowed the energy transfer from donor to acceptors. Hence, based on the synergistic effect of dielectric property and energy transfer resulting in efficient charge separation, our finding paves an alternative path to elucidate the physical working mechanism in non-fullerene-based photovoltaic devices.