Organic Devices Research Articles

A spectroscopic assessment of static and dynamic disorder in a film of a polythiophene with a planarized backbone.

The optoelectronic performance of organic semiconductor devices is related to the static and dynamic disorder in the film. The disorder can be assessed by considering the linewidth of its optical spectra. We focus on identifying the effect of conjugation length distribution on the static energetic disorder. Hence, we disentangle the contributions of static and dynamic disorder to the absorption and emission spectra of poly(3-(2,5-dioctylphenyl)-thiophene) (PDOPT) by exploring how the linewidth and energy of the spectra evolve upon cooling the sample from 300 K to 5 K. PDOPT has sterically hindered side chains that arrange such as to cause a planarized polymer backbone. This makes it a suitable model for a quasi-one-dimensional molecular system. By modelling the conjugated segments as coupled oscillators we find that the linewidth contribution resulting from the variation of conjugation length decreases linearly with decreasing exciton energy and extrapolates to zero at the energy corresponding to an infinite chain. These results provide a new avenue to the design of low disorder and hence high mobility polymeric semiconductors.

Fabrication of Li-Doped NiO Thin Films by Ultrasonic Spray Pyrolysis and Its Application in Light-Emitting Diodes

The fabrication of NiO films by different routes is important to extend and improve their applications as hole-transporting layers in organic and inorganic optoelectronic devices. Here, an automated ultrasonic pyrolysis spray method was used to fabricate NiO and Li-doped NiO thin films using nickel acetylacetonate and lithium acetate dihydrate as metal precursor and dimethylformamide as solvent. The effect of the amount of lithium in the precursor solution on the structural, morphological, optical, and electrical properties were studied. XRD results reveal that all the samples are polycrystalline with cubic structure and crystallite sizes in the range of 21 to 25 nm, without any clear trend with the Li doping level. AFM analysis shows that the crystallites form round-shaped aggregates and all the films have low roughness. The optical transmittance of the films reaches values of 60% to 77% with tendency upward as Li content is increased. The electrical study shows that the films are p-type, with the carrier concentration, resistivity, and carrier mobility depending on the lithium doping. NiO:Li (10%) films were successfully incorporated into inorganic light emitting diodes together with Mn-doped ZnS and ZnO:Al films, all deposited on ITO by the same ultrasonic spray pyrolysis technique.

A Flexible Organic Electrochemical Synaptic Transistor With Dopamine-Mediated Plasticity

Artificial synapses relying on electrical and optical stimuli to implement neuromorphic tasks have been intensively developed, but very few of them can directly respond to real biological neurotransmitter stimulus, thus limiting the seamless integration of bio-electronic interfaces. In this letter, we report a flexible organic electrochemical transistor-based synaptic device, which demonstrates not only short-term synaptic behaviors dominated by the kinetics of ions but also long-term synaptic behaviors derived from the redox reaction of dopamine neurotransmitters. More importantly, we systematically studied the dopamine-mediated synaptic plasticity under both flat and bending states, which shows reliable synaptic response and excellent mechanical flexibility. These results reveal that our device providing a promising way for direct biohybrid integration with soft biological tissues.

Recent Developments of Organic Optoelectronic Functional Materials and Devices Based on Biphenyl Derivatives

Recent Developments of Organic Optoelectronic Functional Materials and Devices Based on Biphenyl Derivatives

Boosting electron transport in non-fullerene acceptors using non-chlorinated solvents

Chlorinated solvents are commonly used to process organic semiconductor devices but have several negative environmental impacts.

PEDOT and PEDOT:PSS thin-film electrodes: patterning, modification and application in stretchable organic optoelectronic devices

This review mainly focuses on patterning strategies and modification methods for better electrical and mechanical properties of PEDOT-based thin-film electrodes as well as their applications in stretchable organic optoelectronics.

A light-triggered molecular switch for an efficient OFET-based organic memory device

An efficient OFET-based memory is designed using spiropyran molecular switch operating via two complementary mechanisms: reversible photoisomerization and light-induced electron transfer involving [Cr(C2O4)3]3− counterion.

Recent progress in flexible electrodes and textile shaped devices for organic solar cells

This review summarized the current development of flexible electrodes applied to organic solar cells and the latest research on fiber and fabric-shaped organic solar cell devices, including detailed information on their fabrication technologies.

2023: Year of Re‐Debut

2023: Year of Re‐Debut

Exciton regulation mechanism of Alq<sub>3</sub>/HAT-CN tandem electroluminescent devices

Tandem organic electroluminescent devices (OLEDs) have attracted widespread attention due to their long lifetime and high current efficiency. In this study, a double-emitting unit tandem OLED is fabricated by using Alq<sub>3</sub>/HAT-CN as an interconnect layer. Its photovoltaic properties and exciton regulation mechanism are investigated. The results show that the luminance (11189.86 cd/m<sup>2</sup>) and efficiency (13.85 cd/A) of the tandem OLED reaches 2.7 times that of the single electroluminescent (EL) unit OLED (luminance and efficiency of 4007.14 cd/m<sup>2</sup> and 5.00 cd/A, respectively) at a current density of 80 mA/cm<sup>2</sup>. This proves that the Alq<sub>3</sub>/HAT-CN is an efficient interconnect layer. At room temperature, the polaron pair undergoes intersystem crossing (ISC) due to hyperfine interaction (HFI) when a magnetic field is applied to the device. This increases the concentration of the triplet excitons (T<sub>1</sub>), thus promoting the charge scattering. The result is a rapid increase in the low magnetic field and a slow increase in the high magnetic field of the MEL. When the injection current strength is constant, there is less uncompounded charge in the Alq<sub>3</sub>/HAT-CN device than in other connected layer devices. Triplet-charge annihilation (TQA) is weak, resulting in a relative increase in the value of T<sub>1</sub>, which is not involved in the TQA. This suppresses the ISC and leads to a minimal increase in the MEL. As the current strength increases, the T<sub>1</sub> value increases, causing TQA to increase and ISC to decrease. Since the TQA is related to charge and T<sub>1</sub> value, lowering the temperature reduces the carrier mobility in the device, resulting in the relative decreasing of charge concentration and the weakening of TQA. Lowering the temperature reduces the quenching of thermal phonons and increases the T<sub>1</sub> value while extending its lifetime, resulting in the enhancement of triplet-triplet annihilation (TTA). At low temperatures, the high magnetic field shape of the MEL changes from slowly increasing to rapidly decreasing. Therefore, the T<sub>1</sub> value can be regulated by varying the current strength and temperature, which further affects the strength of ISC, TQA and TTA, and the luminescence and efficiency of the device can be effectively improved by reducing TQA and ISC. This work is of great significance in understanding the luminescence mechanism of small molecule tandem devices and studying the mechanism for improving their photovoltaic properties.

A high-performance dual-functional organic upconversion device with detectivity approaching 1013 Jones and photon-to-photon efficiency over 20.

Organic upconversion devices (UCDs) are a cutting-edge technology and hot topic because of their advantages of low cost and convenience in the important applications of near-infrared (NIR) detection and imaging. However, to realize utilization of triplet excitons (T1), previous UCDs have the drawback of heavily relying on toxic and costly heavy-metal-doped emitters. More importantly, due to poor performance of the detecting unit and/or emitting unit, improving their detectivity (D*) and photon-to-photon conversion efficiency (ηp-p) is still a challenge for real applications. Here, we report a high-performance dual-functional purely organic UCD that has an outstanding D* approaching 1013 Jones and a high ηp-p of 20.1% in the NIR region, which are some of the highest values among those reported for UCDs. The high performance is credited to the excellent D* of the detecting unit, exceeding 1014 Jones, and is also attributed to efficient T1 utilization via a dual reverse intersystem crossing channel and high optical out coupling achieved via a high horizontal dipole ratio in the emitting unit. The high D* and ηp-p enable the UCD to detect 850 nm light at as little as 0.29 μW cm-2 and with a high display contrast of over 70 000 : 1, significantly improving the potential of practical applications of UCDs in NIR detection and imaging. Furthermore, a fast rise time and fall time of 8.9 and 14.8 μs are also achieved. Benefiting from the high performance, consequent applications of low-power pulse-state monitoring and fine-structure bio-imaging are successfully realized with high quality results by using our organic UCDs. These results demonstrate that our design not only eliminates dependence of UCDs on heavy-metal emitters, but also takes their performance and applications to a high level.

Buckybowl and its chiral hybrids featuring eight-membered rings and helicene units.

Here we report the synthesis of a novel buckybowl (7) with a high bowl-to-bowl inversion barrier (ΔG‡ = 38 kcal mol-1), which renders the rate of inversion slow enough at room temperature to establish two chiral polycyclic aromatic hydrocarbons (PAHs). By strategic fusion of eight-membered rings to the rim of 7, the chiral hybrids 8 and 9 are synthesized and display helicity and positive and negative curvature, allowing the enantiomers to be configurationally stable and their chiroptical properties are thoroughly examined. Computational and experimental studies reveal the enantiomerization mechanisms for the chiral hybrids and demonstrate that the eight-membered ring strongly affects the conformational stability. Because of its static and doubly curved conformation, 9 shows a high binding affinity towards C60. The OFET performance of 7-9 could be tuned and the hybrids show ambipolar characteristics. Notably, the 9·C60 cocrystal exhibits well-balanced ambipolar performance with electron and hole mobilities of up to 0.19 and 0.11 cm2 V-1 s-1, respectively. This is the first demonstration of a chiral curved PAH and its complex with C60 for organic devices. Our work presents new insight into buckybowl-based design of PAHs with configurational stability and intriguing optoelectronic properties.

Anisotropic etching by electrospray for reduction in parasitic resistance of organic field-effect transistors

Productive manufacturing that uses a roll-to-roll process, called printed electronics, is highly demanded for low-cost, large-area, and high-speed fabrication of organic devices. However, although most studies on the printing process have been focused on the deposition of films, few studies are reported on solution methods for anisotropic etching that are compatible with the printing process. Studying anisotropic etching by using a wet process is a matter of great importance for the further development of printed electronics. Here, we conduct anisotropic etching by using an electrospray method, one of the wet processes, on an underlying active layer beneath source and drain electrodes and demonstrate a reduction in the parasitic resistance of organic field-effect transistors. The same equipment for the etching as the deposition of films was consistently used. Therefore, this study will pave the way for sophisticating printed electronics. • TIPS pentacene/PMMA blend films and PMMA etch masks were prepared by ESD. • We conducted anisotropic etching by using an electrospray method (a wet process). • Underlying TIPS pentacene beneath source/drain electrodes was selectively etched. • We demonstrated a clear reduction in the parasitic resistance of top-contact OFETs. • The same ESD system for the etching as the deposition of films was consistently used.

Study of mechanical degradation of freestanding ALD Al2O3 by a hygrothermal environment and a facile protective method for environmentally stable Al2O3: toward highly reliable wearable OLEDs.

Al2O3 deposited via atomic layer deposition (ALD) has been used as an insulating and barrier film for thin-film transistors, organic electronics, and microelectromechanical systems. However, ALD Al2O3 films are easily degraded by hydrolysis under harsh hygrothermal conditions, owing to their poor environmental stability. In this study, the mechanical properties and water-vapor transmission rate (WVTR) of environmentally degraded Al2O3 films were investigated by varying the temperature and relative humidity (RH). The hygrothermal environment led to surface and pinhole-concentrated degradation based on aluminum hydroxide, which caused an increased WVTR and reduced elongation of the films in harsher environments. In particular, the elongation of the degraded Al2O3 films was reduced to 0.3%, which is one-third of that of as-deposited Al2O3, and their WVTR increased on the order of 10-1 g m-2 day-1, which is more than 1000 times that of as-deposited Al2O3. Therefore, we introduced a functional silane-based inorganic-organic hybrid layer (silamer) onto the Al2O3 films to improve their environmental stability. The silamer helped preserve the characteristics of Al2O3 films by forming a strong and continuous aluminate phase of Al-O-Si at their interface in hygrothermal environments. Furthermore, the silamer-capped Al2O3 was shown to be an environmentally stable encapsulation for application in wearable organic devices.

Gram-scale polymer-based thermoelectric module for charging Li-ion batteries

Organic thermoelectric devices are promising for charging Li-ion batteries in state-of-art sensors and communication devices. Herein, we report the design and fabrication of a gram-scale polymer-based thermoelectric module prepared by lamination of ultrathin half-dried poly(3,4-ethylenedioxythiophene)/poly(styrenesulfonate) (PEDOT/PSS) films with Ni foils. The hot pressing of a half-dried PEDOT/PSS film increases the film electrical conductivity and decreases its contact resistance. Such devices exhibit a power density of 72 μW/cm2 at 100 °C under natural cooling conditions in the absence of a heat sink. A 5 g device is capable of fully charging a commercial Li-ion battery (Nichicon SLB03070LR35) within 2 days. The manufactured organic thermoelectric device can be used instead of a CR2032 coin cell to power commercial sensors of acceleration, geomagnetism, temperature, humidity, atmospheric pressure, and illuminance. The manufactured devices exhibit excellent stability for over 2 months under continuous operation conditions. This work highlights the potential of organic thermoelectric devices for energy harvesting.

Study on the preparation process and sintering performance of doped nano-silver paste

AbstractAfter tin–lead solders are banned, the widely used electronic packaging interconnect materials are tin–silver, tin–copper, and other alloy solders. With the application of high-power devices, traditional solders can no longer meet the new requirements. Nano-silver (Ag) paste, as a new solder substitute, exhibits excellent properties, such as excellent thermal and electrical conductivity, sintering at lower temperatures, and service at high temperatures. However, many organic devices still cannot withstand this temperature, and are often not suitable for the connection of nano-Ag paste packaging materials, therefore, it is very urgent to further reduce the sintering temperature of nano-silver paste. Based on the transient liquid phase sintering technology, by doping the nano-Ag paste with the nano-tin paste with a lower melting point to make the two uniformly mix, pressureless sintering at low temperature can be realized, and a sintered joint with a connection strength greater than 20 MPa can be formed. Considering that tin is easy to be oxidized, and the core–shell material can prevent the oxidation of tin, and at the same time ensure the uniform distribution of tin in silver, the doping scheme of the core–shell structure is determined. Heterogeneous flocculation method refers to the particles with different properties of charges which attract each other and agglomerate. It is a continuous reduction method for preparing core–shell materials. This method has the advantages of mild reaction conditions and less equipment investment, so the heterogeneous flocculation method is selected to prepare Sn@Ag core–shell nano paste. And research its sintering performance and strengthening mechanism.

Investigation on potential applications of thermal activated delayed fluorescence materials in organic electroluminescent devices

In the past few years, organic battery light emitting devices have attracted a lot of attention, showing great application potential. Fluorescence material, phosphorescence material and thermal activated delayed fluorescence (TADF) material, have attracted more and more attention. However, phosphorescent material is limited by the useage of a heavy metal, Ir. So people want to find a more efficient and environmental-friendly material:TADF. TADF polymer can be used as a new type of organic photoelectric functional materials due to its high exciton utilization. This work focuses on the working principle, advantages, applications of TADF materials and the imagination for future applications. OLED emission of different light colors is also worthy of attention, the differences and efficiency of the three colors have sparked discussion as well. On this basis, starting from the luminescence principle and device structure of TADF, the advantages and disadvantages of TADF materials are summarized. Finally, the solution to “aggregation-caused quenching” problem (ACQ) is found, so as to focus on the application of technology and envisage the future application direction.

Metal–Organic Frameworks-Based Analytical Devices for Chiral Sensing and Separations: A Review (2012–2022)

Metal–organic frameworks (MOFs), as high-surface-area materials, have shown promise in various areas of application, such as chiral sensing and separation, due to their flexibility in design and organized porous cages. Researchers have been striving to design and develop high-performance enantiorecognition and separation analytical techniques in chiral science fields. The main aim of this review is to provide a comprehensive overview of chirality, state-of-the-art MOFs in chirality, and chiral analysis in the past decade, 2012–2022. The classification of this review includes chirality, principles of chiral analysis, the attraction of functional materials in chirality, MOFs in chiral analysis, MOFs for designing enantioselective sensors (fluorescence, circular dichroism, quartz crystal microbalance, electrochemical), and MOFs as chiral stationary phases (CSPs) for chromatographic enantioseparation (high-performance liquid chromatography, gas chromatography, and capillary electrochromatography). Finally, this review covers the vital progress of these materials with attention to the available opportunities and challenges in this topic.

High-performance aggregation-induced emission active poly(ether sulfone)s as polymeric electret for energy-saving genuine photonic transistor memory

Next-generation photo-driven memory devices and artificial neuromorphic networks have shown great promise in adopting organic photo-recordable devices because of their tremendous merits, highly tailorable structures, facile processing, and low power consumption. There are generally-two operation approaches, light-assistant and genuine methods, that can be divided into categories based on whether to apply electrical biasing (VGS or VDS) during the photo-programming process. The genuine type manifests glamorous characteristics in optical communication and neural computation due to the exclusion of additional electric consumption. Nevertheless, there is a lack of investigation into the relationship between the genuine photo-programming process and the design strategy of polymeric electrets. This work is the first to employ triphenylamine (TPA)-based aggregation-induced emission (AIE)-active poly(ether sulfone)s as the electret layer of a photonic transistor memory device to elaborate photo-induced programming. Every chemical building block, AIE-active TPA, ether, and sulfone moieties, has been soundly elucidated and plays an indispensable role in possessing high-performance homopolymer-based photonic memory, including enhancement of photo-induced recording, outstanding retention (14 days), and reducing the working voltage (VGS = 0 V and VDS = −5 V). This study presents an eye-catching design strategy for creating polymer-based photonic memory that also satisfies energy-saving criteria in practice.

Intermolecular coupling enhanced thermopower in single-molecule diketopyrrolopyrrole junctions

<p indent="0mm">Sorting out organic molecules with high thermopower is essential for understanding molecular thermoelectrics. The intermolecular coupling offers a unique chance to enhance the thermopower by tuning the bandgap structure of molecular devices, but the investigation of intermolecular coupling in bulk materials remains challenging. Herein, we investigated the thermopower of diketopyrrolopyrrole (DPP) cored single-molecule junctions with different coupling strengths by varying the packing density of the self-assembled monolayers (SAM) using a customized scanning tunneling microscope break junction (STM-BJ) technique. We found that the thermopower of DPP molecules could be enhanced up to one order of magnitude with increasing packing density, suggesting that the thermopower increases with larger neighboring intermolecular interactions. The combined density functional theory (DFT) calculations revealed that the closely-packed configuration brings stronger intermolecular coupling and then reduces the highest occupied molecular orbital (HOMO)-lowest unoccupied molecular orbital (LUMO) gap, leading to an enhanced thermopower. Our findings offer a new strategy for developing organic thermoelectric devices with high thermopower.