Applications In Organic Optoelectronic Devices Research Articles

New conjugated copolymer MEH-PPV-P3HT with donor-acceptor system for organic optoelectronics applications: Experimental and theoretical study

Donor-acceptor architecture was designed of new diblocks copolymer MEH-PPV-P3HT synthesis. The new copolymer was elaborated through oxidative pathway. The correlation structure-properties and their potential photophysical characteristics of the obtained material were reported utilizing several characterization analyses (InfraRed, Raman, TGA, UV visible spectroscopy, as well as PL and TRPL). To define the model's geometric structure, vibrational, and optoelectronic properties of the studied copolymer, Density Functional Theory DFT and Time-dependent Density Functional Theory TD-DFT approach were carried out. The obtained copolymer exhibits great thermal stability and substantial absorption in the visible range. An energy gap lower than the original materials by the amount of 1.74 eV which proves the presence of the charge transfer process. In addition, due to Forster energy transfer from the MEH-PPV to the P3HT an enhancement of the exciton average lifetime was detected. The obtained results from the copolymer characterization suggest a potential for application in organic optoelectronic devices. A good accordance between experimental and theoretical results based DFT calculations is obtained.

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.

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.

First principles study of 2-(acetoxy group)benzoic acid under different extremely high-pressure environments

Based on Density Functional Theory (DFT), a first-principles study was conducted on the crystal structure, electronic structure, and optical properties of the organic material 2-(acetoxy group) benzoic acid crystal (C9H8O4) under extremely high pressure ranging from 0 to 300 GPa. The structure study revealed the significant bonding and bond breaking phenomena at pressures of 80 GPa and 270 GPa, respectively, indicating that it may induced the lattice phase transitions. The energy band analysis demonstrated that the crystal underwent a transition from a direct bandgap semiconductor at 0 GPa to an indirect bandgap semiconductor at 80 GPa, and then at 270 GPa, the crystal exhibited a metallic phase with a bandgap of 0. The density of states (DOS) provided evidence that this crystal undergo intricate phase transitions under extremely high pressure. The optical properties were further compared and analyzed. It was observed that the peak of optical absorption shifted towards higher energy regions, while the peak of photoconductivity and Loss function shifted towards the blue shift. These findings indicate that extremely high pressures can effectively modulate the structure and properties of C9H8O4 material. This research offers valuable insights for further exploration of the properties of C9H8O4 materials and their potential applications in organic optoelectronic devices.

Isotropic and Anisotropic Complex Refractive Index of PEDOT:PSS.

In this work, the complex refractive indexes of seven PEDOT:PSS samples, three with isotropic behavior and four with optical anisotropy, were determined. For the anisotropic samples, the ordinary and extraordinary components of the refractive index were described. The effect of the film thickness, measurement technique and preparation method on the extinction coefficient (k) and refractive index (n) of each sample was also discussed. Important differences (up to 20% in the average n) were found among the samples investigated. In most anisotropic films, the mean value of the extraordinary component was between 7 and 10% higher than that of the ordinary. In the three isotropic films, the average k rose when the film thickness increased. Moreover, the different sets of refractive index data were fitted to three different models: the original Forouhi-Bloomer model, the Liu (2007) model and the revised version of the Forouhi-Bloomer model (2019). In general, Liu's model gave better results, with small errors in n and k (<7.81 and 4.68%, respectively, in all the cases). However, this model had seven fitting parameters, which led to significantly longer computation time than the other two models. The influence of the differences in the measurement of the complex refractive index on the simulation of the optical properties of PEDOT:PSS multilayers was discussed. The results showed that n must be known precisely to accurately calculate the light absorption in a multilayer, without ignoring the isotropic or anisotropic behavior of the material or the influence of the layer thickness on its optical properties. This study aids in the development of simulation and optimization tools that allow understanding the optical properties of PEDOT:PSS films for their potential applications in organic optoelectronic devices, such as organic solar cells.

Synthesis and properties of a novel decacyclic S,N-heteroacene.

S,N-Heteroacene materials with fused multicyclic heteroaromatics have become increasingly attractive for organic optoelectronic device applications. In this work, the Cadogan ring-closure reaction between the benzene moiety of thieno[3,2-b]indole and 5,6-dinitrobenzo[c][1,2,5]thiadiazole was employed to prepare the novel decacyclic S,N-heteroacene 15,16-dibutyl-14,17-didodecyldithieno[2'',3'':2',3']indolo[6',7':4,5]pyrrolo[3,2-e:2',3'-g][2,1,3]benzothiadiazole (TIP), C58H76N6S3. The conjugated backbone of TIP is extended in comparison with its octacyclic analogue as the central unit within Y6-type molecular acceptors, a family of overwhelming electron acceptors in polymer solar-cell research. The single-crystal X-ray diffraction (SC-XRD) characterization indicated the existence of π-π and C(sp2)-H...π interactions among TIP molecules. The electrochemical and optical properties of TIP were also characterized. As a novel S,N-heteroacene building block, TIP is anticipated to be of potential use in the construction of promising electronic materials.

Synthesis, Structure, and Significant Energy Gap Modulation of Symmetrical Silafluorene-Cored Tetracyanobutadiene and Tetracyanoquinodimethane Derivatives.

A series of symmetrical tetracyanobutadiene and tetracyanoquinodimethane derivatives with a D-A-D'-A-D structural configuration and silafluorene core (D') were designed and readily synthesized via a [2+2] cycloaddition-retroelectrocyclization (CA-RE) reaction. We found that the photophysical properties and HOMO and LUMO energy levels and gaps of the silafluorene derivatives could be profoundly remolded through CA-RE reactions and modulated by varying the peripheral donor units from phenyl, m-dimethoxyphenyl, and N,N-dimethylaniline to triphenylamine groups. After CA-RE reactions, the HOMO-LUMO gaps of 1a-1j are in the range of 1.75-2.78 eV, with significant decreases of 0.52-1.46 eV compared to those of the parent silafluorene compounds 2a-2j. The intriguing crystal structures of 1f and 1j were analyzed and elucidated to show their unique potential porosity. The stability, electrochemical, and computational studies were systematically performed to unveil the reshaped electron-donating and -withdrawing nature in one molecular system. 1h-1j with peripherally strong amino donors exhibit an intense and broad intramolecular charge transfer absorption band in the near-infrared region from 550 to 900 nm. The molecular design and synthesis reported here broaden the types and fields of D-A molecular systems for potential applications in organic optoelectronic devices.

The Stoichiometry of TCNQ-Based Organic Charge-Transfer Cocrystals

Organic charge-transfer cocrystals (CTCs) have attracted significant research attention due to their wide range of potential applications in organic optoelectronic devices, organic magnetic devices, organic energy devices, pharmaceutical industry, etc. The physical properties of organic charge transfer cocrystals can be tuned not only by changing the donor and acceptor molecules, but also by varying the stoichiometry between the donor and the acceptor. However, the importance of the stoichiometry on tuning the properties of CTCs has still been underestimated. In this review, single-crystal growth methods of organic CTCs with different stoichiometries are first introduced, and their physical properties, including the degree of charge transfer, electrical conductivity, and field-effect mobility, are then discussed. Finally, a perspective of this research direction is provided to give the readers a general understanding of the concept.

Research progress of rubrene as an excellent multifunctional organic semiconductor

Rubrene, a superstar in organic semiconductors, has achieved unprecedented achievements in the application of electronic devices, and research based on its various photoelectric properties is still in progress. In this review, we introduced the preparation of rubrene crystal, summarized the applications in organic optoelectronic devices with the latest research achievements based on rubrene semiconductors. An outlook of future research directions and challenges of rubrene semiconductor for applications is also provided.

Synthesis and Characterization of AIE-Active B–N-Coordinated Phenalene Complexes

Organoboron compounds provide a new line to tune the electronic structures of π-conjugated molecules, which is critical to the development of new organic semiconductor materials. In this work, we demonstrate the synthesis of two novel boron–nitrogen (B−N) coordinated phenalene complexes (BNP-PX and BNP-PA) by employing BN phenalene (BNP) as the acceptor unit and phenoxazine/phenylphenazine groups as the donors. Based on single-crystal X-ray analysis, both BNP-PX and BNP-PA possess highly twisted conformations with the dihedral angles of 76.6 ° and 70.5 °, respectively. The photophysical properties of BNP-PX and BNP-PA are elucidated through UV-vis absorption, fluorescence spectroscopy, and theoretical calculations. In addition, BNP-PX exhibits a large Stokes shift (8,033 cm−1) and excellent aggregated-induced emission behavior. The red organic light-emitting diode device was fabricated based on compound BNP-PX, manifesting its promising application in organic optoelectronic devices.

Graphene as a Transparent and Conductive Electrode for Organic Optoelectronic Devices

AbstractGraphene is emerging as one of the most useful electrode materials for various organic optoelectronic devices because of its outstanding properties such as high optical transparency, excellent mechanical flexibility, good electrical conductivity, and environmental stability. Numerous synthesis and transfer techniques used to obtain large‐area and high‐quality graphene materials are demonstrated, aiming at high‐performance graphene‐based organic optoelectronic devices such as solar cells, light‐emitting diodes, and field‐effect transistors. The properties, synthesis, and transfer processes of graphene are first introduced. Recent research progress on organic optoelectronic devices with graphene bottom, top, and full electrodes is then reviewed. Finally, graphene composite electrodes integrated with other conductive materials are also summarized. All these advanced works represent important steps in the evolution of graphene electrodes and indicate a bright future for their application in organic optoelectronic devices.

High Electron Affinity Molecular Dopant CN6-CP for Efficient Organic Light-Emitting Diodes.

p-Type molecular doping of organic materials with high ionization energies (IEs) of above 5.50 eV is still a challenge, limiting the use of doping in high-performance organic light-emitting diodes (OLEDs). Here, we investigate the molecular dopant hexacyano-trimethylene-cyclopropane (CN6-CP) with a high electron affinity of 5.87 eV as p-dopant in OLEDs. We show that CN6-CP can be used not only as a dopant in the traditional hole transport material 4,4'-cyclohexylidenebis[ N, N-bis(4-methylphenyl)benzenamine] (TAPC, IE = 5.50 eV) but also effectively dopes the host material tris(4-carbazoyl-9-ylphenyl)amine (TCTA, IE = 5.85 eV), reaching a conductivity of 1.86 × 10-4 S/cm at a molar ratio of 0.25. Using CN6-CP-doped TAPC as hole injection and transport layer, we achieve a low driving voltage of 2.92 V at the practical brightness of 1000 cd/m2 and 3.18 V at a current density of 10 mA/cm2 for a green phosphorescent OLED based on bis[2-(2-pyridinyl- N)phenyl- C](acetylacetonato)iridium(III) (Ir(ppy)2(acac)), together with a maximum external quantum efficiency of 18% and a luminous efficacy of 78 lm/W. The device also exhibits a very low efficiency roll-off at high luminance. Further, by directly adopting CN6-CP-doped TCTA as the injection/transport layer, the driving voltage drops to 2.78 V at 1000 cd/m2 and 2.93 V at 10 mA/cm2. Moreover, conductivity and absorption measurements suggest that CN6-CP could also dope CBP with an IE as high as 6.05 eV. The results show that CN6-CP is an excellent p-type dopant for efficient OLEDs and possesses great potential for future application in organic optoelectronic devices.

Flexible transparent conducting electrodes based on metal meshes for organic optoelectronic device applications: a review

Metal mesh: a design that revolutionizes the transparent conducting electrode (TCE) industry and drives the development of flexible optoelectronic technology.

Effects of the Substituents of Boron Atoms on Conjugated Polymers Containing B←N Units.

Organoboron chemistry is a new tool to tune the electronic structures and properties of conjugated polymers, which are important for applications in organic optoelectronic devices. To investigate the effects of substituents of boron atoms on conjugated polymers, we synthesized three conjugated polymers based on double B←N-bridged bipyridine (BNBP) with various substituents on the boron atoms. By changing the substituents from four phenyl groups and two phenyl groups/two fluorine atoms to four fluorine atoms, the BNBP-based polymers show blue-shifted absorption spectra, decreased LUMO/HOMO energy levels, and enhanced electron affinities, as well as increased electron mobilities. Moreover, these BNBP-based polymers can be used as electron acceptors for all-polymer solar cells. These results demonstrate that substituents of boron atoms can effectively modulate the electronic properties and applications of conjugated polymers.

Fine-Tuning LUMO Energy Levels of Conjugated Polymers Containing a B←N Unit

The LUMO and HOMO energy levels (ELUMO/EHOMO) are key parameters for conjugated polymers, which can greatly affect their applications in organic opto-electronic devices. In this manuscript, with donor–acceptor (D–A) type conjugated polymers based on double B←N bridged bipyridine (BNBP) unit, we report fine-tuning of ELUMO of conjugated polymers in a wide range via substitutions on both D unit and A unit. We synthesize eight D–A type conjugated polymers with alternating electron-deficient BNBP unit and electron-rich bithiophene (BT) unit in the main chain. By changing the substitutes on BNBP or BT, the ELUMO of these polymers can be finely tuned in a wide range from −3.3 eV to −3.7 eV. We comprehensively investigate the electronic structures, photophysical properties, charge-transporting properties and polymer solar cell (PSC) device applications of these polymers. In PSC devices, these BNBP-based polymers can be used either as electron donors (with high-lying ELUMO/EHOMO) or as electron acceptors (with lo...

Induction of Strong Long‐Lived Room‐Temperature Phosphorescence of N‐Phenyl‐2‐naphthylamine Molecules by Confinement in a Crystalline Dibromobiphenyl Matrix

AbstractThe design and preparation of metal‐free organic materials that exhibit room‐temperature phosphorescence (RTP) is a very attractive topic owing to potential applications in organic optoelectronic devices. Herein, we present a facile approach to efficient and long‐lived organic RTP involving the doping of N‐phenylnaphthalen‐2‐amine (PNA) or its derivatives into a crystalline 4,4′‐dibromobiphenyl (DBBP) matrix. The resulting materials showed strong and persistent RTP emission with a quantum efficiency of approximately 20 % and a lifetime of a few to more than 100 milliseconds. Bright white dual emission containing blue fluorescence and yellowish‐green RTP from the PNA‐doped DBBP crystals was also confirmed by Commission Internationale de l'Eclairage (CIE) coordinates of (x=0.29–0.31, y=0.38–0.41).

Induction of Strong Long-Lived Room-Temperature Phosphorescence of N-Phenyl-2-naphthylamine Molecules by Confinement in a Crystalline Dibromobiphenyl Matrix.

The design and preparation of metal-free organic materials that exhibit room-temperature phosphorescence (RTP) is a very attractive topic owing to potential applications in organic optoelectronic devices. Herein, we present a facile approach to efficient and long-lived organic RTP involving the doping of N-phenylnaphthalen-2-amine (PNA) or its derivatives into a crystalline 4,4'-dibromobiphenyl (DBBP) matrix. The resulting materials showed strong and persistent RTP emission with a quantum efficiency of approximately 20 % and a lifetime of a few to more than 100 milliseconds. Bright white dual emission containing blue fluorescence and yellowish-green RTP from the PNA-doped DBBP crystals was also confirmed by Commission Internationale de l'Eclairage (CIE) coordinates of (x=0.29-0.31, y=0.38-0.41).

(Invited) Synthesis and Characterization of Photoactive Porphyrin Electropolymers

The design and development of new polymeric functional material for application in organic optoelectronic devices, like polymer solar cells, is one of the most active areas of research, mainly due to the continuous search for low cost renewable energy sources. Flexibility, solution processability, and short energy payback time, are among the very important characteristics of the organic based materials that make possible their application in large area devices. However, despite the facts that high power conversion efficiencies have been attained with bulk heterojunction structures, and that the potentiality of the organic photovoltaic technology is still huge, to date industrial production and large scale commercialization have not been achieved, a major issue being the transfer of the efficiencies obtained on small area cells to large area modules. Thus, the development of new polymeric materials and devices construction methods are still necessary, in order to find procedures that allow the implementation of this relevant technology. One of the principal difficulties that the use of organic polymers in electronics has to face is the film deposition methodology over the conducting or semiconducting contacts. The most common approaches rely on thermal evaporation and solution-processing methods. However, thermal evaporation requires materials with adequate sublimation capability and thermal stability, properties that are difficult to reach in polymers. Also, solution processes, such as dip - or spin - coating methodologies, require polymeric materials with intrinsic high solubility. On the contrary, electropolymerization of suitable photoelectroactive monomers allows the synthesis and formation of polymeric films in one step, with the possibility to get control over pattern and thickness, two very important aspects in the implantation of industrial processes. In the last years we developed porphyrin polymeric materials, produced by electrochemical methods. These materials exhibited photovoltaic and electrochromic properties. The monomers were planned with the aim to achieve their polymerization through dimerization of the electrochemically generated tryphenyl amine and/or carbazole radical cations, giving rise to tetraphenylbenzidine and/or dicarbazole substructures with hole transport capability. These polymers demonstrate their capacity for the generation of photoinduced charge separated states, with light absorption in a broad region of the visible spectrum, and hold the potentiality for their application in the development of optoelectronic devices.

Two-dimensional core-shell donor-acceptor assemblies at metal-organic interfaces promoted by surface-mediated charge transfer.

Organic charge transfer (CT) complexes obtained by combining molecular electron donors and acceptors have attracted much interest due to their potential applications in organic opto-electronic devices. In order to work, these systems must have an electronic matching - the highest occupied molecular orbital (HOMO) of the donor must couple with the lowest unoccupied molecular orbital (LUMO) of the acceptor - and a structural matching, so as to allow direct intermolecular CT. Here it is shown that, when molecules are adsorbed on a metal surface, novel molecular organizations driven by surface-mediated CT can appear that have no counterpart in condensed phase non-covalent assemblies of donor and acceptor molecules. By means of scanning tunneling microscopy and spectroscopy it is demonstrated that the electronic and self-assembly properties of an electron acceptor molecule can change dramatically in the presence of an additional molecular species with marked electron donor character, leading to the formation of unprecedented core-shell assemblies. DFT and classical force-field simulations reveal that this is a consequence of charge transfer from the donor to the acceptor molecules mediated by the metallic substrate.