Field Of Organic Optoelectronics Research Articles

Solution-Processed ZnO with Conductivity over 1000 S cm-1 for ITO-Free Organic Photovoltaics.

Developing transparent conductors to replace indium tin oxide (ITO) is a critical objective in the field of organic optoelectronics. Non-atomically doped (NAD) ZnO thin films, while currently exhibiting limited conductivity, are highly promising candidates due to their unique advantages, such as having complete transparency in both the visible and near-infrared spectral regions, solution processability, and the desired surface electronic properties. In this work, the impact of surface modification by insulating polymers on the ultraviolet-enhanced conductivity of NAD-ZnO films is investigated. It was found that polymer modifiers that are rich in amino and hydroxyl groups are effective at increasing the concentration of oxygen vacancies and the conductivity of NAD-ZnO films. The highest conductivity of over 1000 S cm-1, which is more than twice as high as the previous record for NAD-ZnO films, is achieved using polyethylenimine ethoxylated (PEIE) to modify NAD-ZnO films. Subsequently, the replacement of ITO in organic photovoltaic devices by a ZnO/PEIE electrode is realized. The ZnO/PEIE-based OPV devices that were created exhibit performances comparable to those of ITO-based devices under simulated solar illumination and performances better than those achieved with ITO-based devices under simulated indoor illumination. These results make NAD-ZnO a promising candidate for the widespread replacement of ITO in optoelectronic devices.

1,2,5,6‐Naphthalene Diimides: A Class of Promising Building Blocks for Organic Semiconductors†

Comprehensive SummaryOrganic semiconductors have drawn extensive attention due to their optoelectronic properties and wide applications in organic optoelectronics. In comparison with the popular 1,4,5,8‐naphthalene diimides (1,4,5,8‐NDIs), the angular‐shaped 1,2,5,6‐NDIs have exhibited tunable photophysical properties, self‐assembly behaviors and charge transporting properties. Due to these unique features, 1,2,5,6‐NDIs show great potential for construction of high performance π‐functional materials. In this review, we highlight the recent advances and future prospects of 1,2,5,6‐NDI‐based π‐systems in the field of organic optoelectronics, including molecular design, synthesis, structure‐property relationships as well as the applications in high performance organic field‐effect transistors, organic photovoltaics, perovskite solar cells, and so on. What is the most favorite and original chemistry developed in your research group?Chemistry of π‐functional materials by using naphthalene and azulene as the basic structural units.How do you get into this specific field? Could you please share some experiences with our readers?This comes from my previous research experience, independent thinking and academic exchange & discussion. When I was a PhD student, my research topic focused on p‐type organic semiconductors. Since I independently carried out scientific research, my research interest turned to developing more challenging n‐type organic semiconductors by using core‐expanded 1,4,5,8‐naphthalene diimides (NDIs). Later on, 1,2,5,6‐NDIs as high‐performance organic semiconductors, the topic of this review paper, entered our study perspective based on the concept of isomerism. Also, based on the concept of isomerism and academic discussion, azulene, the isomer of naphthalene with unique chemical structure and physicochemical properties, became the dominant building block for constructing novel π‐functional materials in my group.How do you supervise your students?Select a research topic with scientific significance and certain challenges, let students consult and intensively read relevant literatures and obtain research inspiration, basic knowledge, experimental skills, writing skills, etc. Encourage students to think independently, try more, and pay more attention to communication and cooperation. Fully train students to write research papers independently. The last but not the least, advocate the academic spirit of being innovative, pursuing excellence as well as rigorous scholarship.What is the most important personality for scientific research?Curiosity and perseverance.What are your hobbies?Reading and walking.If you have anything else to tell our readers, please feel free to do so.No one can imprison your mind and hold your hand to prevent you from doing research work, follow your heart to do what you like and different from others.

Hammer throw-liked hybrid cyclic and alkyl chains: A new side chain engineering for over 18 % efficiency organic solar cells

Side chain engineering has been commonly recognized to be a simple and effective strategy in designing organic photovoltaic materials and increasing power conversion efficiencies. Different from recent traditional side chain modulation, this work presented the design and synthesis of a family of fresh hybrid side chain by combining the relatively rigid cyclic and flexible alkyl chain. To be specific, cyclopentane, cyclohexane and cycloheptane were introduced to the tail of the alkyl side chain, through which novel polymer donors D18-C6Cp, D18-C6Ch and D18-C6Chp were prepared based on the excellent skeleton of D18. In comparison with simplex cyclic or branched chain, hybrid side chains with preferential conformations were capable of impacting the self-assembling characteristics and facilitating the interpenetrating networks of blend films, thereby contributing to high-efficiency charge transport, lower energy loss, and inhibited charge recombination. Strikingly, the D18-C6Ch:L8-Bo-based single junction OPV cells reveal a prominent FF of 78.7 %, and a Voc of 0.91 V with the maximum PCE up to 18.2 %. This work exhibits an effective hybrid side chain engineering to synergistically tune the self-assembly properties and finally improve organic photovoltaic performance, which would be a broad potential in developing novel materials in the field of organic optoelectronics.

Impact of the substitution pattern of the acceptor on the properties of the bis(trifluoromethyl)phenyl disubstituted aromatic diamines

New aromatic diamines with bis(trifluoromethyl)phenyl substituents were synthesized and investigated. Theoretical and experimental results revealed that compounds containing 2,5-bis(trifluoromethyl)benzene moiety exhibit interplay between inductive and mesomeric effects opening new possibilities in the field of organic optoelectronics. Furthermore, the CF3 group at ortho position leads to the closer packing of molecules in the single crystal as well as in the amorphous state. As a result, CF3 group decreases the ionization potential and enhance the hole mobilities of the synthesized compounds containing 2,5-bis(trifluoromethyl)benzene moieties as compared to their counterparts containing 3,5-bis(trifluoromethyl)benzene moieties.

Construction of sublimable pure organic ionic material with high solid luminescence efficiency based on anion-π+ interactions tuning strategy

Charged species with π-conjugated moieties play a vital role in the development of organic electronic field, but the executable strategy of attaining high luminescent efficiency with sublimable pure organic salts is rare due to their inherent ionic nature and low vapor pressure, extremely restricting their application in the field of organic optoelectronics via common vacuum evaporation method. In this work, a series of central-type organic salts based polycyclic aromatic hydrocarbon (PAH) core are developed because of their potential higher luminescence efficiency than that of reported terminal-type organic salts like protonated pyridine framework, and they are equipped with aggregation-induced emission enhancement performance and tunable emission. The analyses of spectral data, crystal packing, and theoretical simulation demonstrate that rationally dispersing surface charge of large π cation by regulating donor–acceptor (D-A) distribution facilitates to increase anion-π+ interactions and suppress the free rotation of phenyl groups, contributing to the fluorescence enhancement in the solid state. Notably, after tuning counter-ions’ steric hindrance and dispersed charges (BArF24−), the sublimable pure organic ionic materials are obtained with high solid luminescence efficiency, and its vacuum-evaporated organic light-emitting diode (OLED) is prepared based on pure organic salt with bright yellow emission. Such inspiring results offer us new alternative material system for the organic optoelectronics.

Self-recovering mechanochromic luminescence of the derivatives of benzanthrone and carbazole: Towards damage-resistive information recording and security probes

Discovery of organic luminophores with unique properties typically leads to new applications of such emitters in the field of organic optoelectronics. The example is demonstrated in this study. One of the newly synthesized mechanochromic derivatives of benzanthrone and carbazole demonstrates ability of self-regulation of its solid-state structure and related light-emitting properties. This compound shows intensive green emission peaking at 537 nm in the initial state, weak yellowish green emission peaking at 557 nm after mechanical treatment which self-recovers back to intensive green emission with the intensity maximum at 539 nm. The processes are completely reversible. They include the following set of states: highly emissive state → damaged weak-emissive state → self-recovering → recovered highly emissive state. The developed compound is a very rare example of materials which can be used for security probes or data/code writing with recovering ability after mechanical damage. Variety of experimental studies including spectroscopy of thermally annealed samples and single crystal and powder diffraction X-ray analysis revealed the ability of the developed derivatives of benzanthrone and carbazole to form different polymorphs and aggregates in solid-state responsible for their multicolour mechanochromic emission.

Growing two-dimensional single crystals of organic semiconductors on liquid surfaces

Two-dimensional (2D) organic semiconducting single crystals (OSSCs) combine the advantages of OSSCs and 2D molecular materials, and currently, are an important and hot research topic in the field of organic optoelectronics and 2D materials. Growth of large-sized 2D OSSCs with controlled thickness is highly important for fundamental research and practical application, which is still a challenging task. Liquid surfaces can provide ideal platforms for growth of large-scale and layer-controlled 2D OSSCs because their surfaces are molecularly flat and free-defect, the “coffee-ring” effect can be effectively suppressed on liquid surfaces, and the improved spread area of organic semiconductor solutions on liquid surfaces. This perspective concentrates on recent advances in the growth of large-area and layer-controlled 2D OSSCs on liquid surfaces; the optoelectronic applications based on 2D OSSCs, as well as the challenges and outlooks in the field, are also discussed.

Molecular self-assembly and fluorescence change of donor-acceptor cocrystal based on naphthalimide derivatives

<p indent="0mm">Organic cocrystals formed by two or more components through π-π interactions, charge transfer, and hydrogen/halogen bondings have attracted extensive attention because of their applications in the field of organic optoelectronics. Here, we prepared three charge-transfer cocrystals by solution-process self-assembly method which used Coronene and pyrene as donors, <italic>N</italic>,<italic>N</italic>′-dimethyl-1,4,5,8-naphthalenetetracarboxylic diimide (NDI-1) and <italic>N</italic>,<italic>N</italic>′-bis(ethyl)-1,4,5,8-naphthalenetetracarboxylic diimide (NDI-2) as acceptors. Detailed structural characterizations clarified the mixed stacking mode in the charge-transfer cocrystals, and the supramolecular network was stabilized by C–H···O hydrogen bonds and π<italic>-</italic>π interactions. Interestingly, compared with the original donors, three cocrystals show different fluorescence emissions, which is related to the formation of charge-transfer states between donors and acceptors. This cocrystal strategy provides a new opportunity for the design of new organic light-emitting charge-transfer complexes.

The Impact of UV Photoelectron Spectroscopy on the Field of Organic Optoelectronics—A Retrospective

AbstractThe field of organic electronics has been of widespread interest for a long time. Over the years, device efficiencies increased steadily due to the development of new materials, as well as an improved understanding of the physical mechanisms governing underlying fundamental processes such as charge transport or charge carrier generation and recombination. Especially the positions of energy levels that are responsible for the charge transport throughout a device are of paramount importance. This generated a high demand for reliably measured values. The most important technique that can directly access these values in a thin film is photoelectron spectroscopy. The very fruitful collaboration between surface scientists and device specialists is ​ reviewed here, showing a range of experiments through which UV photoelectron spectroscopy helped to unravel the working mechanisms of organic semiconductors in devices.

Comparative opto-electronic properties of perylene diimides derivatives with cyclization and high polarizability cores

Recently, perylene diimides (PDIs) show great application potentials in the field of organic opto-electronics, which can be widely used in OLEDs, OPVs, OFETs, etc. In order to obtain more efficient PDIs derivatives, there are two typical methods including cyclization and high polarizability cores. However, numerous valuable molecules cannot be experimental synthesized easily, which are available for theoretical prediction via simulation and calculation. Therefore, we design four model molecules of PDIs derivatives, whose opto-electronic properties are calculated by the DFT method afterwards. By comparing simulation results, we can further extend the comprehension of structure-property relationships of PDIs, which is beneficial to the high-efficiency PDIs derivatives design.

Multifunctional Benzo[4,5]thieno[3,2-b]benzofuran Derivative with High Mobility and Luminescent Properties.

Development of multifunctional materials and devices has garnered enormous attention in the field of organic optoelectronics; nevertheless, achieving high mobility together with strong luminescence in a single semiconductor remains a major bottleneck. Here, a new multifunctional semiconductor molecule, 2,7-diphenylbenzo[4,5]thieno[3,2-b]benzofuran (BTBF-DPh), that integrates high charge transporting [1]benzothieno[3,2-b][1]benzothiophene with a strongly emissive furan group, is synthesized and applied in three types of optoelectronic devices, including organic light-emitting diodes (OLEDs), organic field-effect transistors (OFETs), and organic phototransistors (OPTs). OLEDs based on BTBF-DPh as the emissive layer showed a blue emission with CIE coordinates of (0.151, 0.069) and a maximum current efficiency of 2.96 cd A-1 with an external quantum efficiency of 4.23%. Meanwhile, OFETs fabricated with BTBF-DPh thin film manifested a carrier mobility of 0.181 cm2 V-1 s-1, which is comparable to that of thiophene-based counterparts. Additionally, BTBF-DPh-based OPTs exhibited a maximum responsivity and detectivity of 2.07 × 103 A W-1 and of 5.6 × 1015 Jones, respectively. On the one hand, our rationally designed material, BTBF-DPh, has a dense and close-packed structure with an extended π-conjugation, facilitating charge transport through adjacent molecules. On the other hand, the weakened dipole-dipole interactions between BTBF-DPh molecules that resulted from the unambiguous J-aggregation and reduced spin-orbit coupling caused by replacing sulfur atom significantly suppress the exciton quenching, contributing to the improved photoluminescence performance. These results validate that our newly developed BTBF-DPh is a promising multifunctional organic semiconductor for optoelectronic devices.

Simultaneous studies of pressure effect on charge transport and photophysical properties in organic semiconductors: A theoretical investigation

High-mobility and strong luminescent materials are essential as an important component of organic photodiodes, having received extensive attention in the field of organic optoelectronics. Beyond the conventional chemical synthesis of new molecules, pressure technology, as a flexible and efficient method, can tune the electronic and optical properties reversibly. However, the mechanism in organic materials has not been systematically revealed. Here, we theoretically predicted the pressure-depended luminescence and charge transport properties of high-performance organic optoelectronic semiconductors, 2,6-diphenylanthracene (DPA), by first-principle and multi-scale theoretical calculation methods. The dispersion-corrected density functional theory (DFT-D) and hybrid quantum mechanics/molecular mechanics (QM/MM) method were used to get the electronic structures and vibration properties under pressure. Furthermore, the charge transport and luminescence properties were calculated with the quantum tunneling method and thermal vibration correlation function. We found that the pressure could significantly improve the charge transport performance of the DPA single crystal. When the applied pressure increased to 1.86 GPa, the hole mobility could be doubled. At the same time, due to the weak exciton coupling effect and the rigid flat structure, there is neither fluorescence quenching nor obvious emission enhancement phenomenon. The DPA single crystal possesses a slightly higher fluorescence quantum yield ∼ 0.47 under pressure. Our work systematically explored the pressure-dependence photoelectric properties and explained the inside mechanism. Also, we proposed that the external pressure would be an effective way to improve the photoelectric performance of organic semiconductors.

Hydroxy-benzimidazoles as blue-green emitters: Synthesis, structural and DFT studies

The new benzimidazole ligands (3a-e) were synthesized using ethyl 4-(butylamino)-3-nitrobenzoate and substituted salicylaldehyde in the presence of sodium dithionite reagent which undergoes “one-pot’’ nitro reductive cyclization. Here benzimidazole moiety acts as an electron-acceptor (A) whereas substituted 2-hydroxyphenyl moiety acts as an electron-donor (D) unit. The molecular structures were characterised by FTIR, 1H NMR, 13C NMR, single crystal XRD and MS analysis. Optoelectronic properties were determined by UV–vis, solution and solid photoluminescence, quantum yield and lifetime. The solvent-dependent absorption and emission were studied using both polar protic and polar aprotic solvents. All the derivatives exhibited ESIPT, especially compound ethyl 1-butyl-2-(3,5-dichloro-2-hydroxyphenyl)-1H-benzo[d]imidazole-5-carboxylate (3e) displayed dual emission in both polar protic and polar aprotic solvents. The compound stability and electrochemical property were determined by thermal gravimetric analysis (TGA) and cyclic voltammetry (CV) respectively. The compounds emit intense blue-green fluorescence with high to moderate quantum yield. Also, these derivatives exhibited a high Stokes shift. The computational studies like Density-Functional Theory (DFT) and Molecular Electrostatic Potential (MEP) were conducted to provide important insights into the structure-property relationships. The crystal packing is stabilized through intermolecular hydrogen bonds (C---H…O) and intermolecular interactions (π… π). The findings of results help in developing novel ligands in the field of organic optoelectronics.

Physical and Chemical Properties of Dimedone “Base Schiff” for Organic Semiconductor Applications

One pot synthesis of “Schiff” base is carried out in this study. The synthesis by using microwave reaction as a modern method is realized from 4-dimehtylamino-5,5-dimethyl-1,3-cyclohexanedione, benzene 1.4-diamine and 1,3-benzodioxole-5-carbaldehyde. The structural properties of the resulting compound were determined by NMR (1H and 13C), low-resolution mass spectrometry (ESI–MS), FTIR spectroscopy and x-ray diffraction. The product is semicrystalline material with a monoclinic unit cell. Based on the optical spectra, the compound has an optical band gap of (Eg = 2.89 eV). In addition, the dielectric spectroscopy was applied for studying the ac-electrical conductivity, dielectric constant and dielectric losses of the synthesized “Schiff” base. The results obtained from this study show that it has a promising future in the field of organic optoelectronics and their potential applications especially in photovoltaic conversion energies.

Negatively Curved Warped Nanographene Self-Assembled on Metal Surfaces.

We report the investigation of a conjugated polycyclic hydrocarbon containing multiple nonbenzenoid rings and exhibiting negative curvature-the warped nanographene C80H30-adsorbed on several noble metal surfaces in an ultrahigh vacuum environment. From a detailed analysis of the molecular self-assembly at different molecular coverages via scanning tunneling microscopy and spectroscopy measurements in combination with theoretical modeling, the nature of the intermolecular interactions is unraveled. For high molecular coverages on Cu(111), the formation of homochiral porous networks is observed, which is rationalized by (i) intermolecular π-π interactions between neighboring C80H30 molecules that promote the formation of molecular dimers and (ii) enantioselective intermolecular CH···π interactions between the dimers. Such interactions are also observed after deposition of C80H30 molecules on Au(111) and Ag(111) substrates. Our results provide perspectives for the on-surface study of negatively curved nanographenes whichopen new avenuestothe design of novel and functional chiral structures with potential use in the field of organic optoelectronics.

Multiple short pulse process for low-temperature atomic layer deposition and its transient steric hindrance

Low-temperature atomic layer deposition (ALD) is increasingly used in the field of organic optoelectronics. However, the deposition of ALD outside the temperature window still cannot be stably implemented. In this study, transient steric hindrance caused by gas-phase molecules at low-temperature (80 °C and 30 °C) was investigated. In order to mitigate the effect of this transient hindrance, a process of consecutive short-pulses was adopted in our experiments. As a result, the density of Alucone films increased from 2.21 g/cm3 to 2.37 g/cm3 and the density of room-temperature deposited Al2O3 films increased 28.6% from 2.41 g/cm3 to 3.1 g/cm3. Overall, the proposed idea would help low-temperature ALD become mature and be widely promoted.

Phenothiazine-Based Oligo(p-phenylenevinylene)s: Substituents Affected Self-Assembly, Optical Properties, and Morphology-Induced Transport.

Designing intramolecular charge-transfer (ICT)-based luminogenic ordered assemblies exhibiting significant electrical transport is a challenging task in the field of organic optoelectronics. In this context, a series of novel phenothiazine-based oligo(p-phenylenevinylene) (OPV1-6) derivatives were designed and their structure-property relationship was investigated. Upon examining their photophysical properties, all the OPVs were found to exhibit significant intramolecular charge-transfer characteristics in organic solvents. While inspecting the self-assembly behaviour, the OPV with a long alkyl chain on the central phenyl core (OPV4) underwent gelation in organic solvent mixtures through strong hydrophobic interactions of the long hexadecyl chains and π-interactions from their aromatic counterparts. Computational studies revealed a lamellar packing of molecules in the assembly. Interestingly, the degree of ICT and the gelation abilities of OPVs were significantly influenced by the electronic nature of the substituents appended to the peripheral phenothiazines. Further, the AC impedance results revealed an increase in storage and electronic transport for the fluorescent thin films prepared by an increase in the content of OPV4 in PMMA.

Thieno[3,4-b]thiophene-Based Novel Small-Molecule Optoelectronic Materials.

Because of the tailorable photoelectric properties derived from judicious molecular design and large-area and low-temperature processability especially on flexible substrates, design and synthesis of new organic π-functional materials is always a central topic in the field of organic optoelectronics, which siginificantly contributed to the development of high-performance optoelectronic devices such as organic photovoltaics (OPVs), organic field-effect transistors (OFETs), and organic light-emitting diodes (OLEDs). Compared with polymers, small molecules with well-defined molecular structures benefit the establishment of structure-property relationships, which may provide valuable guidelines for the design of new optoelectronic materials to further promote the device performance. New building blocks are essential for the construction of optoelectronic materials. As is well recognized, thiophene-based functional materials have played an indispensable role in the development of organic optoelectronics. Compared with six-membered benzene, five-membered thiophene shows weaker aromaticity and lower steric hindrance and may provide extra sulfur-sulfur interactions in solid state. Among various thiophene building blocks, thieno[3,4-b]thiophene (TbT) is an asymmetric fused bithiophene containing four functionalization positions, in which the proaromatic thiophene can effectively stabilize the quinoidal resonance of the aromatic thiophene. Thus, TbT exhibits a unique characteristic of quinoid-resonance effect that is powerful to modulate electronic structures. Although the application of TbT in polymer donor materials represented by PTB-7 has achieved a great success, its application in small-molecule optoelectronic materials is almost an untouched field. In this Account, we summerize the rational design of a series of TbT-based small-molecule optoelectronic materials designed and optimized by quinoid-resonance effect, regiochemistry, and side-chain engineering and demonstrate the crucial effect of TbT building blocks on the electronic structures, photophysical and charge transport properties, and photovoltaic performance. With well-defined regioregular oligothieno[3,4-b]thiopenes, we revealed the quinoid-resonance effect of the TbT moiety and its geometric origin. TbT-based small molecules exhibit full-color tunable emissions in the visible to near-infrared regions and excellent performance in OFETs and OPVs. For instance, TbT-based quinoidal molecules with near-infrared fluorescence quantum yields up to 53.1% and TbT-based aromatic molecules with full-color-tunable emissions and high fluorescence quantum yields approaching 100% in polar solvent were designed and synthesized. Solution-processable ambient-stable n-channel organic thin-film transistors based on two-dimensional π-expanded quinoidal terthiophenes with distal or proximal sulfur orientations (2DQTTs) realized a record electron mobility of 5.2 cm2 V-1 s-1. Furthermore, TbT-based electron donor and electron acceptor materials were successfully designed for OPV applications delivering high power conversion efficiencies up to 9.26% and 10.07%, respectively. We believe that new TbT-based small-molecule materials designed by a synergy of molecular engineering strategy may not only further promote OFET and OPV performance but also realize more unique applications.

Highly Efficient Three Primary Color Organic Single‐Crystal Light‐Emitting Devices with Balanced Carrier Injection and Transport

Organic single crystals have a great potential in the field of organic optoelectronics because of their advantages of high carrier mobility and high thermal stability. However, the application of the organic single crystals in light‐emitting devices (OLEDs) has been limited by single‐layered structure with unbalanced carrier injection and transport. Here, fabrication of a multilayered‐structure crystal‐based OLED constitutes a major step toward balanced carrier injection and transport by introducing an anodic buffer layer and electron transport layer into the device structure. Three primary color single‐crystal‐based OLEDs based on the multilayered structure and molecular doping exhibit a maximum luminance and current efficiency of 820 cd cm−2 and 0.9 cd A−1, respectively, which are the highest performance to date for organic single‐crystal‐based OLEDs. This work paves the way toward high‐performance organic optoelectronic devices based on the organic single crystals.

Organics go hybrid

From displays to solar cells, the field of organic optoelectronics has come a long way over the past 50 years, but the realization of an electrically pumped organic laser remains elusive. The answer may lie with hybrid organic–inorganic materials called perovskites.