Organic Electronics最新文献

There inevitably appear dead zones in organic thin films fabricated by sheet-to-sheet slot-die coating because a coating start varies and the recovery time of internal pressure in slot-die head differs for each coating, resulting in poor coating repeatability. Slot-coated thin films within dead zones are thinner or thicker, possibly causing non-uniform light emission from solution-processable organic light-emitting diodes (OLEDs). To tackle it, we have devised an automatic coating start method based on the monitoring of meniscus formation. It automatically starts coatings when the cross-sectional area of meniscus reaches a certain optimal value in such a way that the start of each coating is kept unchanged. It is found that high-viscosity (4800 cPs) polydimethylsiloxane (PDMS) requires a longer time for the internal pressure of slot-die head to reach a steady state than low-viscosity (80 cPs) poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS). It can be reduced to a great extent by applying a method of discharging the solution in advance (pre-discharging scheme). Compared with high-viscosity PDMS films, low-viscosity PEDOT:PSS films are shown to have longer dead zones and poorer repeatability due to the fact that the dead zone of relatively thin films varies sensitively to a small change in the coating start timing. With this scheme, we have successfully fabricated a highly uniform OLED device with no dead zones in the emission area.

Recent research on anthracene-based hydrocarbon (PNA) as the emissive layer host found that deuteration mediated the formation of these adduct species, presumably quenchers, and thus improved the device lifetime. Meanwhile, studies on deuterium in PNA host materials with stepwise deuteration are scarce. In this work, we report a systematic study of isotopic effects through independent deuteration of the phenyl or/and the dibenzofuran unit on a series of PNA materials polyaromatic dibenzofuran (PAF, PAF-d₅, PAF-d₇ and PAF-d₁₂). We fabricated fluorescent OLED based on this triplet-triplet up-conversion active host materials for conventional MR-TADF emitter. A short-lived excited delayed lifetime of less than 2 μs has been observed in their electroluminescence decay studies. In addition, LT₈₀ of up to 12.7 h has been observed in PAF-d₁₂ at the brightness of 1000 cd m⁻², corresponding to a 4-fold enhancement of OLED stability compared to the non-deuterated counterpart. We hope the current research can provide insights for further device improvement.

In this work, three orthogonally bonded phenanthroimidazole based donor-acceptor (D-A) structured blue-emissive materials N-SBPMCN, N-ABPMCN and N-TBPMCN with different donor moieties are designed synthesized. Theoretical combined experimental researches proved that the involving of weak donor (spiro-fluorene and anthracene) and strong donor triphenylamine can form different locally-emissive (LE) dominated hybrid local and charge-transfer (HLCT) excited state, which can contribute to their high photoluminescent quantum yield (PLQY), satisfied electroluminescence performance and blue purity. Specifically, N-TBPMCN with strong donor triphenylamine that possesses more CT excited state components demonstrates the best electroluminescence performance and blue purity among the three materials, revealing that the molecular design of orthogonal D-A structure is of great potential in blue-emissive functional materials. Additionally, we also discovered that intermolecular CT state can also contribute to high exciton utilization.

Two electron-transport host materials are synthesized by linking anthracene with benzimidazole derivatives through a unit of methyl substituted phenyl. The methyl substitution generates a large dihedral angle between the benzimidazole plane and bridging phenyl, keeping the excited state distribution and energy levels of T₁ and S₁ unchanged. The electron-only devices reveal that the two hosts have obviously enhanced electron transport ability than that of Ph-AN-MBP without benzimidazole. As a result, the devices with Ph-AN-BIZ and N1-AN-BIZ as hosts and a blue multiple resonance material of tBuCz-DABNA as emitter exhibit high external quantum efficiency of 10.1 % and 9.1 %, respectively, and low turn-on voltage of 2.7 V, which is better than those of Ph-AN-MBP based device (7.9 %, 3.4 V). And their electroluminescence spectra have a very small full-width at half-maximum of 16.2 nm and pure blue color with CIE coordinates of (0.12, 0.11).

With the advent of numerous flexible optoelectronic applications, the importance of flexible and stable transparent conducting electrodes (TCEs) has been considerable. The conventional silver nanowire (AgNW) is a promising candidate as TCEs due to its decent opto-electrical properties and solution processibility. However, AgNW's high surface root mean square (RMS) roughness, relatively high sheet resistance, and low work function (∼4.5 eV) limit the usage for display applications. In this work, we design and study the AgNW and MXene (Ti₃C₂T_x) hybrid TCEs for flexible organic light-emitting diodes (OLEDs) to enhance the optoelectrical properties and the hole injection within the device. Experiment investigation is carried out via an application of AgNW/MXene (AgMX) hybrid TCEs as a bottom electrode for OLEDs devices in which the photolithography process and lift-off technique are employed for such fabrication. The hybrid TCEs indicate high optical transparency (86.8 % at 550 nm) and low sheet resistance (24.1 Ω/cm²) as well as improved surface morphology, enabling the efficient OLEDs operation. The optimized OLEDs exhibit a clear and stable red electroluminescence (EL) peak with an improved maximum external quantum efficiency (EQE) and luminance of 5.25 % and 3421.7 cd/m², respectively. Furthermore, the hybrid TCEs are readily formed on poly(ethylene terephthalate) (PET) substrate, showing high durability under the bending test up to 100,000 cycles. The results demonstrate that adopting AgMX TCEs is a reasonable strategy for obtaining proper flexible optoelectronic devices.

A method for preparing a single-layer encapsulation film using an organic-inorganic hybrid precursor solution processing was investigated. The film was created using a commodity epoxy and graphene oxide to ensure cost-effectiveness. Fast curing and annealing techniques, including microwave and intense pulsed light exposure, were employed. Calcium oxide nanoparticles were incorporated as a special moisture absorbent to improve the film's barrier properties. The barrier performance of the single layer encapsulation film was considerably enhanced by post-treatment of these nanoparticles. The characterization of the calcium oxide nanoparticles after post-treatment was performed using transmission electron microscopy with energy-dispersive X-ray spectroscopy, FT-IR, Brunauer-Emmett-Teller test. The composite epoxy encapsulation film, incorporating graphene oxide and post-treated calcium oxide nanoparticles, reduced water permeability approximately 400 times compared to the neat epoxy encapsulation film. This substantial improvement makes it suitable for use in flexible disposable electronics. The enhanced water vapor blocking efficiency is attributed to the combined effect of pathway block by graphene oxide and moisture absorption by calcium oxide.

Organometal halide perovskite solar cells (PSCs) have achieved power conversion efficiencies (PCE) greater than 26 %, making them attractive photovoltaic devices. However, achieving high-performance PSCs typically requires inert gas conditions and antisolvent processes, which are hurdles to the commercialization of PSCs. To overcome these problems, we adopted a vacuum flash-assisted process (VASP) under ambient air conditions. In addition, to minimize the effect of moisture and enhance crystal growth, we adopted an additive engineering strategy using ammonium salts (NH₄X, X = I, Cl, and SCN). Among the various ammonium salts, ammonium iodide (NH₄I) exhibited the best device performance, with a PCE of 19.8 %. The role of the ammonium salts was studied using photoluminescence (PL), scanning electron microscopy (SEM), grazing incidence wide-angle X-ray scattering (GIWAXS), and the device characteristics of the devices. In addition, we measured the wet film state using X-rays to study the effects of ammonium salts on the crystallization process. From these measurements and analyses, we found that the ammonium additives induced rapid crystallization of the perovskite layer, and NH₄I induced a uniform crystalline state of the film in the vertical direction. The uniformity of the crystalline state was related to the reduction in charge recombination and the enhancement of the PCE in the NH₄I added devices.

Low-cost and efficient long-wavelength thermally activated delayed fluorescence (TADF) materials are crucial for organic light-emitting diodes (OLEDs) applications. In this study, 1,8-naphthalimide (NAI)-based D-A-type molecules were explored with a focus on donor engineering. A green-emitting non-TADF original control, the NAI/triphenylamine (TPA) hybrid NAI-TPA, was subjected to structural locking by oxygen-atom bridges on the TPA unit and further adopted an adjacent two-donor configuration to obtain two efficient orange-red/red TADF emitters, NAI-DPXZ and NAI-2DPXZ. The two compounds exhibited both significantly redshifted electroluminescence and improved external quantum efficiency (EQE), reaching 22.12 % at 583 nm and 11.17 % at 622 nm, respectively, which are approximately 2–3 times greater than those achieved by the O-bridges-free controls NAI-TPA (7.38 % at 517 nm) and NAI-2TPA (5.80 % at 564 nm). This work may provide an effective design strategy for the development of high-performance and low-cost orange-red/red TADF materials.

Exploring through-space charge transfer (TSCT) excited state for the design of thermally activated delayed fluorescence (TADF) emitters has been receiving increasing interest for organic light-emitting diodes (OLEDs). In this work, we developed two TSCT-TADF molecules, namely 2DPXZ-QX and 2DPXZ-DFQX, which have sandwich-type donor-acceptor-donor (D-A-D) structures supported by two carbazole bridges. Dibenzo[a,c]phenazine (QX) and its fluorinated derivative (DFQX) were used as the acceptors and O-bridged triphenylamine (DPXZ) was used as the donor. The two donors and acceptor in each molecule are aligned in a face-to-face orientation and thus result in the presence of intramolecular π–π interactions, as revealed by their single crystal X-ray structures. The emission maxima (λ_PL) of 2DPXZ-QX and 2DPXZ-DFQX in doped 1,3-bis(N-carbazolyl)benzene films are 595 and 600 nm with photoluminescence quantum yields of 67 % and 54 %, respectively. The delayed fluorescence lifetimes are 8.8 and 6.7 μs. OLEDs based on the new sandwich-type emitters show maximum external quantum efficiencies of up to 19.1 %.