Organic Optoelectronic Devices Research Articles

Universal Design and Efficient Synthesis for High Ambipolar Mobility Emissive Conjugated Polymers

AbstractHigh ambipolar mobility emissive conjugated polymers (HAME‐CPs) are perfect candidates for organic optoelectronic devices, such as polymer light emitting transistors. However, due to intrinsic trade‐off relationship between high ambipolar mobility and strong solid‐state luminescence, the development of HAME‐CPs suffers from high structural and synthetic complexity. Herein, a universal design principle and simple synthetic approach for HAME‐CPs are developed. A series of simple non‐fused polymers composed of charge transfer units, π bridges and emissive units are synthesized via a two‐step microwave assisted C−H arylation and direct arylation polymerization protocol with high total yields up to 61 %. The synthetic protocol is verified valid among 7 monomers and 8 polymers. Most importantly, all 8 conjugated polymers have strong solid‐state emission with high photoluminescence quantum yields up to 24 %. Furthermore, 4 polymers exhibit high ambipolar field effect mobility up to 10−2 cm2 V−1 s−1, and can be used in multifunctional optoelectronic devices. This work opens a new avenue for developing HAME‐CPs by efficient synthesis and rational design.

From monomer to polymer: Controlled synthesis and comprehensive analysis of poly(p-phenylene vinylene) via ROMP

This study focuses on synthesis and evaluation of [2.2] paracyclophane-1,9-diene to produce a soluble poly(p-phenylenevinylene) (PPV) derivative homopolymer using ring-opening metathesis polymerization (ROMP). The resulting homopolymer displayed a narrow polydispersity index (PDI) of 1.22, indicating precise control over polymerization. The PPV derivative exhibited excellent solubility in various organic solvents. Photophysical properties, including optical absorption and fluorescence emission spectra, were investigated to evaluate utilization in optoelectronic devices. Optical band gaps ranged from 2.21 to 2.25 eV for thin films and 2.07 to 2.19 eV for solutions, while the electrochemical band gap, determined by cyclic voltammetry, was 2.37 eV. These materials demonstrated promising fluorescence activity in various solvents and thin films, suggesting potential applications in organic light-emitting diodes (OLEDs) and related optoelectronic devices.

Investigation on structural, optical, thermal, and dielectric properties of cellulose propionate/styrene-maleic anhydride copolymer/molybdenum nanocomposite prepared by pulsed laser ablation

Polymer nanocomposite films of cellulose propionate/styrene-maleic anhydride copolymer/molybdenum (CP/SMAC/Mo) were fabricated by pulsed laser ablation of Mo in the polymer solution for 10, 20, and 30 min. The films were then characterized by various analytical methods. X-ray diffraction (XRD) revealed that the addition of Mo to CP/SMAC removed the crystalline peaks of Mo without changing the amorphous nature of the copolymer. According to the scanning electron microscopy (SEM) and atomic force microscopy (AFM) patterns, Mo atoms were trapped in the amorphous polymer stacks. The energy-dispersive X-ray (EDX) spectrum features C, O, and Mo. FTIR confirmed the embedding of Mo in the polymers. Thermogravimetric analysis (TGA) and differential thermal analysis (DTA) were carried out on the samples. The pristine polymer film exhibited a band gap energy of 2.9 eV, which decreased to 2.05 eV because of the loading of the Mo nanoparticles. The intensity of the photoluminescence (PL) peak of the films increases with ablation time such that the absorption intensity of the film at a λmax of 426 nm increases by trifold during the 30 min of irradiation, which is consequently due to the increased amount of Mo in the nanostructure. The incorporation of Mo in the polymer matrix enhances the dielectric constant (ε') (6.28–18.13) and ac conductivity (σac) (3.19 × 10−5–1.12 × 10−4 S/cm) of the polymer with negligible dielectric loss. The results suggest possible technological utilization of these materials in such applications as supercapacitors, light-emitting diodes, and organic optoelectronic devices, among others.

Aqueous solution processed transition-metal-doped ZnO as electron injection layers for efficient inverted organic light emitting diodes

Zinc oxide (ZnO) has attracted lots of attention to be used as interfacial materials in organic optoelectronic devices owing to its attractive properties. In this work, a series of transition-metal-doped ZnO thin films were prepared by using a facile aqueous solution process, thereafter these films were employed as electron injection layers (EILs) combined with the tris-(8-hydroxyquinoline) aluminum (Alq3) emitting layer to construct the inverted organic light-emitting diodes (IOLEDs). The transition-metal-doped ZnO EIL-based IOLEDs demonstrate markedly improved device performance compared to the reference neat ZnO EIL-based IOLED. However, different transition-metal ions have much different doping effect on the device performance. CoCl2 doped ZnO EIL based IOLED device possesss an optimal current efficiency of 5.52 cd A−1, which is increased about 40% compared to the device with the neat ZnO as EIL. The enhancement might be attributed to the increased electron mobility and favorable interfacial energy level alignment of the transition-metal doped ZnO EIL for more efficient electron injection. Our findings may provide a promising strategy to improve the electron injection properties of ZnO film in the OLED devices.

Electropolymerization and characterization of a new ambipolar perimidine polymer with a perylene core

We successfully synthesized a stable electroactive perinone polymer by electropolymerization from the mixture of syn- and anti- isomers (ratio 1:1) of 3,4:9,10-bis(1,8-naphthapyrimidine)-1,6,7,12-tetrakis(1,1,3,3-tetramethylobutylphenoxy)perylene (NPP). The polymer p(NPP) exhibited distinct redox process, with reduction at -1.20 V and oxidation at 0.60 V (vs. ferrocene/ferrocenium couple). Spectroscopic and computational analyses confirmed structural similarity of the polymer to its monomeric form, revealing a perimidine unit involved in electrocoupling. Our thorough investigations elucidated the redox reactions electrochemical mechanism within the polymer film, identifying predominantly deprotonated bis-perimidine segments contributing to oxidation peaks at 0.60 V and 0.68 V. Additionally, the perylenediamide core exhibits the reversible, multi-stage reduction process. Impedance analysis highlighted efficient n-doping-induced conductivity, suggesting application in organic optoelectronic devices. This work positions p(NPP) as a versatile ambipolar multiredox p- and n-type conductor, indicating a potential for expanding perinone-based perylene-diperimidine polymers for innovative electronics.

Highly reliable and stretchable OLEDs based on facile patterning method: toward stretchable organic optoelectronic devices

Stretchable displays attract significant attention because of their potential applications in wearable electronics, smart textiles, and human-conformable devices. This paper introduces an electrically stable, mechanically ultra-robust, and water-resistant stretchable OLED display (SOLED) mounted on a stress-relief pillar platform. The SOLED is fabricated on a thin, transparent polyethylene terephthalate (PET) film using conventional vacuum evaporation, organic-inorganic hybrid thin film encapsulation (TFE), and a nonselective laser patterning process. This simple and efficient process yields an OLED display with exceptional stretchability, reaching up to 95% strain and outstanding durability, enduring 100,000 stretch-release cycles at 50% strain. Operational lifetime and water-resistant storage lifetime measurements confirm that the TFE provides effective protection even after the nonselective laser patterning process. A 3 × 3 array SOLED display module mounted on a stress-relief pillar platform is successfully implemented, marking the first case of water-resistant display array operation in the field of SOLEDs. This work aims to develop practical stretchable displays by offering a reliable fabrication method and device design for creating mechanically robust and adaptable displays, potentially paving the way for future advances in human-conformable electronics and other innovative applications.

Peripheral Selenium Modification of Multi‐Resonance Thermally Activated Delayed Fluorescence Molecules for High‐Performance Blue Organic Light‐Emitting Diodes

AbstractMulti‐resonance thermally activated delayed fluorescence (MR‐TADF) molecules have attracted much attention in the academia owing to their unique photoelectrical properties. However, MR‐TADF emitters usually show slow reverse intersystem crossing (RISC) rate, resulting in high efficiency roll‐off of organic light‐emitting diodes (OLEDs) and seriously limiting their further development. Here, a peripheral selenium (Se) modification is presented for MR‐TADF molecules to promote the RISC process while keeping the narrowband emission for high‐performance blue OLEDs. Compared to the parent molecules (NBN and tBuNBN), SeNBN and SetBuNBN exhibited narrower full‐width at half maximum (FWHM) value of 23 nm and more obvious delayed fluorescence properties with a high efficiency of delayed fluorescence up to 86%, shorter delayed lifetime of 2.4 µs as well as a faster RISC rate of 3.34×105 s−1. Therefore, high‐performance OLEDs based on these two Se modified MR‐TADF emitters are achieved with a high maximum external quantum efficiency (EQE) up to 25.5% and extremely suppressed efficiency roll‐offs of 3.9% at 100 cd m−2 and 24.4% at 1000 cd m−2. This work demonstrated that the introduction of peripheral Se atom can achieve high‐performance organic semiconductors with both narrowband emission and fast RISC rate constant for high‐performance organic optoelectronic devices.

Visualization of Nanocrystallites in Organic Semiconducting Blends Using Cryo-Electron Microscopy.

The efficiency of an organic solar cell is highly dependent on the complex, interpenetrating morphology, and molecular order within the composite phases of the bulk heterojunction (BHJ) blend. Both these microstructural aspects are strongly influenced by the processing conditions and chemical design of donor/acceptor materials. To establish improved structure-function relationships, it is vital to visualize the local microstructural order to provide specific local information about donor/acceptor interfaces and crystalline texture in BHJ blend films. The visualization of nanocrystallites, however, is difficult due to the complex semi-crystalline structure with few characterization techniques capable of visualizing the molecular ordering of soft materials at the nanoscale. Here, it is demonstrated how cryo-electron microscopy can be utilized to visualize local nanoscale order. This method is used to understand the distribution/orientation of crystallites in a BHJ blend. Long-range (>300nm) texturing of IEICO-4F crystallites oriented in an edge-on fashion is observed, which has not previously been observed for spin-coated materials. This approach provides a wealth of quantitative information about the texture and size of nanocrystallites, which can be utilized to understand charge generation and transport in organic film. This study guides tailoring the material design and processing conditions for high-performance organic optoelectronic devices.

Unveiling the Strain‐induced Microstructural Evolution and Morphology‐Stretchability Correlations of Intrinsically Stretchable Organic Photovoltaic Films

AbstractThe progress of stretchable and wearable photovoltaics relies heavily on intrinsically stretchable active layer films. Nevertheless, there is a paucity of research clarifying the connections between their microstructure, performance, and their adaptation to large strain in polymer electronic films. The current study utilizes multiple synchrotron X‐ray scattering methods to collectively examine the correlations between morphology and stretchability, as well as the microstructural evolution induced by stretching in three sample cases of highly stretchable ternary blend films. These blends contain over 30% by weight of a polymer elastomer, such as styrene‐ethylene‐butylene‐styrene block copolymer, integrated into the high‐performance polymer:nonfullerene small molecule mixture. Specifically, the real‐time microstructural changes of these durable organic photovoltaic films with elastomers are monitored when subjected to tensile stretching through in situ synchrotron X‐ray scattering. The experiments demonstrate that polymeric elastomers can effectively lower the degree of crystallinity in films and deform the crystallites of semiconductor molecules. The elastomeric component aids in stress dispersion during stretching, thereby improving the microstructural durability of blend films. This study provides new recommendations for advancing stretchable organic optoelectronic devices.

Surface‐Initiated Living Self‐Assembly of Polythiophene‐Based Conjugated Block Copolymer into Erect Micellar Brushes

AbstractNanostructured conjugated polymers are of widespread interest due to their broad applications in organic optoelectronic devices, biomedical sensors and other fields. However, the alignment of conjugated nanostructures perpendicular to a surface remains a critical challenge. Herein, we report a facile method to directly self‐assemble a poly(3‐(2‐ethylhexyl)thiophene), P3EHT‐based block copolymer into densely aligned micellar brushes through surface‐initiated living crystallization‐driven self‐assembly. The presence of an ethyl pendant on the side group intrinsically moderates the crystallization rate of the polythiophene main chains, and hence favors the controlled living growth of long conjugated fibers and the subsequent fabrication of conjugated micellar brushes. The corona of the micellar brush can be further decorated with platinum nanoparticles, which enables the formation of erect nanoarrays with heights up to 2700 nm in the dried state. This also renders the micellar brush catalytically active toward hydrogen evolution reaction, which shows a low overpotential of 27 mV at 10 mA cm−2. Notably, the P3EHT‐based micellar brush can simultaneously grow with polyferrocenyldimethylsilane, PFS‐based micellar brush on the same surface without any significant interference between the two systems. Thus, these two micellar brushes can be patterned through site‐selective immobilization of two types of seeds followed by independent living self‐assembly.

Surface-Initiated Living Self-Assembly of Polythiophene-Based Conjugated Block Copolymer into Erect Micellar Brushes.

Nanostructured conjugated polymers are of widespread interest due to their broad applications in organic optoelectronic devices, biomedical sensors and other fields. However, the alignment of conjugated nanostructures perpendicular to a surface remains a critical challenge. Herein, we report a facile method to directly self-assemble a poly(3-(2-ethylhexyl)thiophene), P3EHT-based block copolymer into densely aligned micellar brushes through surface-initiated living crystallization-driven self-assembly. The presence of an ethyl pendant on the side group intrinsically moderates the crystallization rate of the polythiophene main chains, and hence favors the controlled living growth of long conjugated fibers and the subsequent fabrication of conjugated micellar brushes. The corona of the micellar brush can be further decorated with platinum nanoparticles, which enables the formation of erect nanoarrays with heights up to 2700 nm in the dried state. This also renders the micellar brush catalytically active toward hydrogen evolution reaction, which shows a low overpotential of 27 mV at 10 mA cm-2 . Notably, the P3EHT-based micellar brush can simultaneously grow with polyferrocenyldimethylsilane, PFS-based micellar brush on the same surface without any significant interference between the two systems. Thus, these two micellar brushes can be patterned through site-selective immobilization of two types of seeds followed by independent living self-assembly.

Comprehensive analysis of DFT-3C methods with B3LYP and experimental data to model optoelectronic properties of tetracene

Modern computational chemistry methods aid experimentalists in scrutinizing molecular systems for organic optoelectronic device fabrication. They are also helpful for device engineering, such as choosing metals for contact fabrication without sophisticated instrumentation. The B3LYP functional with 6-31G(d,p) or 6-311G(d,p) basis set is a widely used method in this regard. Recently, many upgraded methods, such as the three-fold corrected composite scheme (3C), have been reported to offer cost-effectiveness and better accuracy than the B3LYP. This is particularly interesting from a materials engineering point of view as these methods offer the possibility of rapidly screening the materials prior to the experimental analysis. In order to evaluate their suitability towards organic optoelectronic systems, in this work, we have used three composite schemes, namely B97-3C, PBEh-3C and HF-3C, along with B3LYP and the experimental data. The well-studied tetracene system is considered for the analysis, and different optoelectronic properties such as bandgap, reorganization energy, and absorption maximum are calculated theoretically and compared with the experimental data. The results indicate that though slightly expensive, B3LYP performs better than the 3C methods. Of the three, only PBEh-3C performs on par with B3LYP in accuracy and time. A note of caution is that these results should be inferred as this level of theory is adequate for the screening and modeling optoelectronic systems rather than a potential computational chemistry method.

Counterion Engineering toward High-Performance and pH-Neutral Polyoxometalates-Based Hole-Transporting Materials for Efficient Organic Optoelectronic Devices.

Although protonated polyoxometalates (POMs) are promising hole-transporting layer (HTL) materials for optoelectronic devices owing to their excellent hole collection/injection property, pH neutrality, and noncorrosiveness, POMs are seldom used as high-performance HTL materials. Herein, we designed and synthesized a series of mixed-additive POMs with pH-neutral counterions (NH4+, K+, and Na+) as HTL materials. X-ray photoelectron spectroscopy and single-crystal X-ray analyses indicated that the use of the lacunary heteropolyanion [P2W15O56]12- as an intermediate ensured successful incorporation of the counterions into the mixed-addenda POMs without causing deterioration of the POM frameworks. The hole-transporting layer performance of POM-NH4, which was characterized by a high work function and good conductivity and could be prepared using a low-cost method surpassed those of its protonated counterpart POM-4 and many classic HTL materials. An organic solar cell (OSC) modified with POM-NH4 delivered a power conversion efficiency of 18.0%, which was the highest photovoltaic efficiency achieved by POM-based OSCs to date. Moreover, an HTL material based on POM-NH4 reduced the turn-on voltage of an organic light-emitting diode from 4.2 to 3.2 V. The results of this study suggest that POMs are promising alternatives to the classic HTL materials owing to their excellent hole-collection ability, low costs, neutral nature, and high-chemical stability.

Solvent Doping Organic Single Crystal Enables High‐Performance Optoelectronic Devices

AbstractOrganic doping has become an effective method to improve the performance of organic optoelectronic devices. However, the understanding of organic doping mechanism is limited by the difficulty in obtaining highly ordered molecular packing structure. Herein, a new donor‐acceptor type triphenylamine‐acetylene‐based isoindigo derivative, (E)‐6,6′‐bis((4‐(diphenylamino)phenyl)ethynyl)‐[3,3′‐biindolinylidene]‐2,2′‐dione (BDPEBD), is successfully designed and synthesized. The tetrahydrofuran solvent doped BDPEBD single crystal with a mass fraction of 4.33% is easily obtained through a solvent evaporation method. Tetrahydrofuran, as a dopant in its single crystal, effectively reduces the dihedral angle of BDPEBD molecules by forming strong intermolecular hydrogen bonds with BDPEBD molecules, which enhances the π–π intermolecular interaction between BDPEBD molecules, thereby resulting in excellent optoelectronic properties of its single crystal. Its phototransistors show the highest mobility of 0.3 cm2 V−1 s−1, wide spectral response from 254 to 790 nm, UV sensitivity, and a response time of 40 ms, the highest photoresponsivity exceeds 7.44 × 106 A W−1.

Organic Optoelectronic Devices Based on Through-Space Interaction

Organic Optoelectronic Devices Based on Through-Space Interaction

Piezochromic luminescence of excimers formed by anthracene plane slip

Excimer materials are frequently applied to organic chemistry, optoelectronic devices and stimulus response. Specific research on the entire process of excimer generation in solid materials, as well as the intricate mechanism of piezochromic luminescence based on excimer, are still absent and need to be examined in-depth through comprehensive experiments. Therefore, we designed an anthracene-based molecule CZPAN, which adopts no overlap area between anthracene molecules in its crystal at ambient conditions, to investigate the piezochromic luminescence behavior and expect the anthracene group to form excimers under high-pressure stimulation. As pressure increases, CZPAN gradually changes from blue monomer luminescence to green excimer luminescence accompanied with the considerably red-shifted emission spectra, and exhibits a discontinuity of fluorescence quenching during the formation of excimers (in the pressure range of 5.3–6.6 GPa). Moreover, the pressure relief process is fully reversible. This study presents abundant piezochromic luminescence of CZPAN and proves that the formation of excimers requires a certain overlap area between molecules. Pursuing the appropriate strength of π–π interactions will thus be the focus of future research on excimer materials of high luminescence efficiency, so that excimers can be better applied in sensors and imaging devices.

Organic near-infrared optoelectronic materials and devices: an overview

Organic near-infrared optoelectronic materials and devices: an overview

Electric-field modulated energy transfer in phosphorescent material- and fluorescent material-codoped polymer light-emitting diodes.

The excited-state energy transfer widely exists in mixed-material systems and devices. The modulation of an electric field on the energy transfer in photoluminescence has been demonstrated. However, to date, no studies on the electric-field modulation of the excited-state energy transfer in organic optoelectronic devices have been reported. Herein, we investigate the effect of an electric field on the energy transfer in the poly(N-vinylcarbazole) (PVK) thin films doped with iridium(iii)[bis(4,6-difluorophenyl)pyridinato-N,C2']-tetrakis(1-pyrazolyl)borate (Fir6) and 5,6,11,12-tetraphenylnaphthacene (rubrene) (PVK:Fir6:rubrene) and the corresponding light-emitting diodes. Combined with the Onsager model describing electric-field enhanced exciton dissociation, we find that the electric field increases the rate of Dexter energy transfer from Fir6 to rubrene in the films and the diodes. The voltage-dependent color shift in the PVK:Fir6:rubrene light-emitting diodes can be explained by the electric-field enhanced Dexter energy transfer from Fir6 to rubrene. Our findings are important for the control of energy transfer process in organic optoelectronic devices by an electric field for desirable applications.

Energy level measurement for organic semiconductors.

Along with the miniaturization and versatility of organic optoelectronic devices, it is desired to achieve a profound comprehension of the charge transport mechanism and even the basic device physics. The basis of these studies is the acquisition of relevant information about energy levels. This review provides a comprehensive analysis of five commonly-used techniques, including cyclic voltammetry, ultraviolet electron spectroscopy, inverse photoemission electron spectroscopy, low energy inverse photoemission spectroscopy and hot electron spectroscopy. According to the advantages and disadvantages, working mechanism, and application conditions, researchers will screen out a reliable and suitable characterization method, quickly and accurately. This should be beneficial for the efficient promotion of organic electronics and save valuable time for the related research studies.

Hole-transporting alternating copolymers for perovskite solar cells: thia[5]helicene comonomer outperforms planar perylothiophene analog

Compared to planar perylothiophene, thiahelicene has been demonstrated as a superior co-monomer for crafting a high-performance semiconducting polymer in n–i–p perovskite solar cells.