Organic Electronics最新文献

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.

Three conjugated copolymers, PDPP-2FTVT, PIID-2FTVT, and PNDI-2FTVT based on the 2,2′-(1E)-1,2-ethenediylbis[3-fluorothiophene] (2FTVT) core with varying acceptor units, diketopyrrolopyrrole (DPP), isoindigo (IID), and naphthalenediimide (NDI) were developed for organic field-effect transistors (OFETs). Combined electron-withdrawing fluorine atoms and vinyl linkage in the 2FTVT unit not only reduce the frontier molecular orbital energies but also extended the absorption profile and planarize the polymer backbone, manifesting synergetic effect on the strengthened molecular interactions and charge-carrier properties. The resulted copolymer, PDPP-2FTVT show highly reliable thin film transistor properties with highest hole mobility of 1.93 cm² V⁻¹ s⁻¹ compared to PIID-2FTV and PNDI-2FTVT. PIID-2FTV copolymer show ambipolar characteristic with hole and electron mobilities of 0.71 and 0.03 cm² V⁻¹ s⁻¹ respectively while PNDI-2FTVT exhibited the highest electron mobility of 0.20 cm² V⁻¹ s⁻¹ among three copolymers. Thin film micro-structure characterization reveal that the three copolymers formed lamellar, edge-on molecular packing (for PDPP-2FTVT and PIID-2FTV), increased crystallinity with smaller π-π stacking distances, and strengthen the planarity after thermal annealing. These results contribute important progresses in solution-processed OFET and could provide a greater possibility of 2FTVT based copolymers for commercial application.

This paper details how two new small molecules, based on phenanthrene, were developed, and tailored for light-emitting device applications. An account is provided of both the compound synthesis and the methodologies employed in device fabrication. The ink formulation was improved by the use of triflate counterions. Standard bottom emitting devices were constructed on ITO glass along with top emitting devices on a sputter coated silver on glass substrate. Both structures exhibit UV emissions from the synthesized molecules. Successful EL emission within the UV spectrum range has been achieved by spray coating these active molecules onto glass slides. The optimized solution-processed devices produce UV emission using a semi-transparent silver nanowire top electrode. This results in electroluminescence (EL) peaking at 398 nm, with a maximum EL emission intensity of 20.5 μW/cm².

The rational design and modification of the buried interface are essential and challenging for high-performance perovskite solar cells (PSCs). TiO₂ is a simple and readily available electron transport layer material, but its surface defects and poor interfacial contact with perovskite layers hinder its widespread application. Here, we propose an effective TiO₂/perovskite interface modification strategy by introducing simple guanidine carbonate (GuaCO₃) onto the surface of TiO₂. Guanidine carbonate can improve the interfacial contact between TiO₂ and perovskite, reduce non-radiative recombination, and enhance carrier extraction. Moreover, the PbI₂ film grown on the TiO₂/GuaCO₃ substrate tended to become porous during the preparation of perovskite films by the traditional two-step method, which facilitated the complete reaction of organic ammonium salts with PbI₂ and promoted the growth of high-quality perovskite films. The experimental results indicate that GuaCO₃ can passivate the interfacial defects of TiO₂/perovskite, as well as reduce the accumulation of interfacial charges. The device modified with GuaCO₃ achieved a power conversion efficiency (PCE) of 23.39 %, which is significantly higher than that of the control device (21.73 %). After storage in an ambient environment at room temperature for 600 h, the unencapsulated device modified with GuaCO₃ retained 78 % of its initial efficiency, while the control device retained only 57 % of its initial efficiency. These results indicate that interfacial modification with GuaCO₃ is an effective strategy for improving the performance of PSCs.

The long-/short-range charge-transfer (LR/SR-CT) type thermally activated delayed fluorescence (TADF) emitter is designed to solve the problem of slow reverse intersystem crossing rate (k_RISC) of the traditional MR-TADF emitter and obtain the full-color emission. However, the introduction of LR-CT transition inevitably leads to the broadening of the emission spectrum. In the design of LR/SR-CT type TADF emitters, it is still quite difficult to balance the smaller singlet-triplet energy gap (ΔE_ST) and the narrower full-width at half-maximum (FWHM). Here, we investigated the LR-CT and SR-CT proportion of LR/SR-CT TADF emitters by adjusting the strength and position of the peripheral electron-donating units on the MR skeleton (TSBA), and prepared three MR-TADF emitters. The investigation of photophysical properties reveals that the increase in the strength and number of donors significantly reduces the ΔE_ST and accelerates the RISC process. The double substitution strategy of the TSBA skeleton effectively reduces the dihedral angle between the MR skeleton and the electron donor unit, and the highest occupied molecular orbital (HOMO)/hole is more distributed on the MR skeleton, which realizes the increase of the excited state SR-CT component. Consequently, the dual-substituted DTPA-TSBA emitter overcomes the contradiction between the small ΔE_ST and the narrow FWHM, and achieves the reduction of both. The corresponding device based on DTPA-TSBA achieved a green light emission with a maximum external quantum efficiency (EQE_max) of 26.2 % and a FWHM of only 55 nm. This work provides profound guidance for the development of high-performance narrowband TADF emitters.

Semitransparent organic photovoltaic (ST-OPV) cells, with their transparency and aesthetic characteristics, demonstrate tremendous application potential in the field of building integrated photovoltaics (BIPVs), such as photovoltaic windows, skylights, and photovoltaic greenhouses. Unlike traditional inorganic materials, the unique absorption characteristics of organic materials enable ST-OPV cells to selectively utilize the solar spectrum, balancing both the power conversion efficiency (PCE) and the average visible transmittance (AVT). With the rapid development of narrow bandgap acceptor materials, the PCE of ST-OPV cells has reached over 13 %, and the AVT has exceeded 20 %. This work reviews the latest progress of ST-OPV cells, summarizes the optimization strategies of high performance ST-OPV cells in terms of active layer engineering, electrode engineering, and device engineering. Finally, some insightful guidelines are provided for future developments in ST-OPV cells from materials, device and commercialization points.