Organic Electronics最新文献

The universal host material with boron acceptor core structure is exceptionally sparse to be designed for red, green, and blue in efficient phosphorescent organic light emitting diodes (PhOLEDs) accompanying white OLEDs, possessing indistinguishable device feature. Herein, two boron acceptors spiro-host materials namely 1'-(4-(dimesitylboranyl)phenyl)-10-phenyl-10H-spiro[acridine-9,9′-fluorene] (TPA-PBM) and 1-(4-(dimesitylboranyl)phenyl)-3′,6′-dimethylspiro[fluorene-9,8′-indolo[3,2,1-de]acridine] (2MeCz-PBM) were designed and synthesized. The designed rigid donor strategy exhibited good device performance among the reported boron donor-spiro-acceptor (D-spiro-A) skeleton for organic light emitting diodes (OLEDs). In particular, we fabricate RGB three-color phosphorescent OLEDs based on TPA-PBM and 2MeCz-PBM. The red devices exhibit a maximum external quantum efficiency (EQE) of nearly 28 % (26.8 % for TPA-PBM and 27.5 % for 2MeCz-PBM), with an electroluminescence spectrum at 608 nm. The green/blue devices obtain maximum EQEs of 21.2 %/15.3 % and 21.8 % 17.3 %, for TPA-PBM and 2MeCz-PBM, respectively. Furthermore, green devices display an extremely low efficiency roll-off with decreasing 1 % and 3 % at luminance of 5000 cd m⁻². Additionally, the two-color white OLED using 2MeCz-PBM exhibits EQE_max and PE_max are 24.5 % and 62.9 lm W⁻¹ respectively, the EQE remain 23.8 % at commercial lighting brightness of 1000 cd m⁻². The WOLED also shows a stable white spectrum with CIE varying range of (0.41, 0.47) to (0.39, 0.46) at 100 cd m⁻² to 15000 cd m⁻². All obtained results confirmed that our targeted molecules have advantage of carrier balance and efficient charge recombination, which might replace many other commercial host materials.

The slow reverse intersystem crossing (RISC) rate in thermally activated delayed fluorescence (TADF) emitters result in extended exciton lifetime and pronounced efficiency loss at high luminance level. To address this limitation, we have developed and characterized a series of novel compounds featuring triazine cores substituted with tert-butyl carbazole moieties at various positions and quantities. The objective here is to fine-tune the charge transfer properties, thereby enhancing the efficiency of the RISC process. Our studies reveal that through-space charge transfer is more effective than long-range through-bond charge transfer in minimizing the singlet-triplet energy gap and accelerating RISC. The optimized compound, 4tCzTrz, exhibits an exceptionally fast RISC rate of 1.02 × 10⁷ s⁻¹ and a high photoluminescence quantum yield of up to 100 %. Solution-processed organic light-emitting diodes (OLEDs) incorporating this molecule have achieved outstanding maximum external quantum efficiencies of around 20 %, whether used as an emitter directly or as a sensitizer to boost overall emission efficiency.

Multi-resonance (MR) thermally activated delayed fluorescence (TADF) materials with planar rigidity show great potential as emitters in organic light-emitting diodes (OLEDs) due to their high photoluminescence quantum yields and narrowband emission. However, their strong intermolecular interaction trends usually result in redshifted and broadened emission spectra as well as low device efficiencies due to the aggregation-caused quenching (ACQ) effect. In this paper, a bulky spirobifluorene unit was appended onto an asymmetric carbazole/diphenylamine-embedded MR skeleton to relieve such trends, thus affording a new MR-TADF blue emitter, BNSF-1. Introducing spirobifluorene significantly relieves the intermolecular interaction trends of MR backbones without affecting their original photophysical properties. The corresponding sensitizer-free OLED devices based on BNSF-1 exhibit narrowband sky-blue electroluminescence peaking at 475 nm with a full width at half-maximum of 25 nm, as well as a maximum external quantum efficiency of 25.9 %. More importantly, BNSF-1 exhibited negligible spectral broadening and ACQ trends as the doping ratio increased. Our work provides a feasible method for constructing doping concentration-insensitive MR-TADF emitters.

A comparative study of the photophysical properties of pristine C₇₀ and two C₇₀ derivatives, including their thermally activated delayed fluorescence (TADF) is reported. It is observed that the addition of a substituent group to the C₇₀ cage-like structure changes both the radiative and the nonradiative rate constants, the change being more pronounced for the nonradiative processes (S₁→S₀ internal conversion and S₁→T₁ and T₁→S₀ intersystem crossings). A new method of TADF analysis (global analysis of time-resolved and steady-state data) is presented and applied. Both derivatives are found to display a less efficient TADF when compared with C₇₀.

Herein, we propose a strategy to enhance the synaptic behavior of neuromorphic devices based on organic electrochemical transistors (OECT) by introducing (3-aminopropyl)triethoxysilane (APT) into the conjugated polymer film channel. Various film analyses utilizing optical and atomic force microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy revealed that the addition of APT to the poly (3-hexylthiophene) (P3HT) film facilitated the formation of highly crystalline P3HT aggregation, thereby suppressing film degradation induced by repetitive ion injection and ejection under gate bias. Furthermore, electrical characterization of the OECT devices incorporating P3HT channels demonstrated an expanded hysteresis region and improved memory characteristics upon APT addition, which contains functional groups with high electron density, favorably influencing synaptic plasticity features such as short-term plasticity (STP), long-term plasticity (LTP), short-term memory (STM), and long-term memory (LTM). Consequently, it led to the fortification and resilience of synaptic behavior in OECTs, positioning them as a promising candidate for neuromorphic devices.

Dual-layer organic solar cells (OSCs), fabricated through sequential-casting with separately dissolved donor and acceptor materials, offer simplified solution preparation and morphology control. However, the poor solubility of organic materials in non-halogenated solvents often results in undesirable vertical component distribution and insufficient donor/acceptor interfaces in non-halogenated solvent-processed dual-layer OSCs, adversely affecting photovoltaic performance and flexibility. In this study, we applied a solvent vapor annealing (SVA) method using CS₂ solvent in o-xylene solvent-processed dual-layer OSCs. The SVA method effectively adjusted the vertical component distribution of the active layer and increased the donor/acceptor interfaces, leading to an improved power conversion efficiency (PCE) of 17.24 %. Additionally, SVA films exhibited superior tensile properties, with a crack onset strain of 5.07 %, surpassing that of the as-cast films (4.32 %), attributed to the stronger interaction between the donor and acceptor layers with more donor/acceptor interfaces. Consequently, large-area (1 cm²) flexible devices achieved a significant efficiency of 14.20 % and maintained excellent mechanical flexibility, with 80 % of the initial efficiency retained after 1000 bending cycles. This work presents an effective approach for fabricating high-performance non-halogenated solvent-processed flexible dual-layer OSCs.

A novel bipolar host molecule di-spiro [fluorene-9,5′-quinolino [3,2,1-de] acridine-9′,9″-fluorene]-2,2″,7,7″-tetracarbonitrile (QACN) featuring an Acceptor-σ-Donor-σ-Acceptor structure was developed. Systematic investigations into its photophysical, electrochemical, and thermal properties unveiled exceptional thermal stability, a three-dimensional spatial configuration, and bipolar carrier transport capability. Employing QACN as the host material in red phosphorescent and thermally activated delayed fluorescent (TADF) organic light-emitting diodes (OLEDs) yielded a maximum external quantum efficiency of 25.3 % and 16.5 %, respectively. Compared with the commercial material TPBi (EQE = 12.0 %, λ_EL = 668 nm) and mCP (EQE = 14.5 %, λ_EL = 652 nm), the TADF OLEDs based on QACN achieved a higher EQE and a large red-shift emission (EQE = 16.5 %, λ_EL = 694 nm). These findings underscore the potential of QACN as an effective host material for red phosphorescent and TADF emitters and provide a new auxiliary finesse for realizing deep red and near-infrared (NIR) OLEDs.

Thermal stability holds significant importance in both high-resolution and large-area organic light-emitting diodes (OLEDs) due to its potential impacts on pixel shrinkage, thereby adversely affecting visual quality and long-term device functionality. The thermal instability could be from the thermal diffusion of metal ions or small molecules occurring at the interface between the electron injection layer (EIL) and the cathode material, influenced by differing surface properties and binding strength. In this study, we meticulously engineered magnesium fluoride (MgF₂) as EIL to mitigate the aforementioned challenges. Important physical properties associated with the EIL/cathode interaction were systematically analyzed. Employing Ag:Yb (2.5:1) as the cathode, we achieved notable enhancements in current efficiency and a reduced turn-on voltage for a green device operating under optical microcavity conditions. Thermal degradation test conducted over 240 h on fabricated devices revealed that employing MgF₂ as the EIL markedly enhanced thermal stability compared to devices utilizing Yb as the EIL reference. The robust EIL/cathode system observed herein is attributed to the high binding energy between the EIL and cathode materials utilized in this study.

In this work, we provide a mechanistic understanding of the degradation of perovskite solar cells in operation by focusing on methylammonium lead triiodide (CH₃NH₃PbI₃ or MAPbI₃) and tracking the evolution of electronic defects via photo-induced current transient spectroscopy (PICTS). Moreover, we also record the degradation of its photovaltaic characteristics over time under various electric load and temperature conditions. Using PICTS, we found that bands of trap states, initially highly localized deep within the band gap of the perovskite, widened over the exposure period. This effect was exacerbated with increasing temperature. Further, using the design of experiment methodology for this multifactorial study, we found that two interaction factors (temperature× load & temperature× time) were significant in the degradation of the perovskite cells, validating the importance of our holistic approach. Through these observations, we establish a mechanistic link between deep-level traps and photovoltaic characteristics.

This work reports theoretical investigations concerning long-range coupling of electron-hole pairs in spatially separated exciplex (SSE) systems via Density Functional Theory and Time-Dependent Density Functional Theory. Based on TCTA−PO-T2T parent exciplex, where 4,4′,4″-Tris(carbazol-9-yl)triphenylamine (TCTA) serves as donor (D) and 2,4,6-Tris[3-(diphenylphosphinyl)phenyl]-1,3,5-triazine (PO-T2T) as acceptor (A), SSEs are constructed by intentionally tuning the D−A distance. The calculation results demonstrate that all SSEs, even if the D−A distance is over 14 Å, exhibit the clear and strong charge transfer character in terms of D_CT, q_CT, and t indexes. As the D−A distance increases, the energy gap of SSEs is increased, resulting in the blueshift of emission spectra. Calculation and experiment results show a good consistency, indicating that our model could well describe SSEs. Meanwhile, the reduced energy gap between CT and ³LE and more degenerate states could boost reverse intersystem crossing via vibronic coupling and hyperfine coupling, eventually improving the electroluminescent performance of SSEs. Our study suggests that manipulation of relative energy alignment via controlling D−A distance not only promotes the properties of exciplexes, but also offers guidance for designing thermally activated delayed fluorescence emitters through-space charge transfer.