High triplet energy level and thermal stability are crucial properties for host materials to fulfill organic light-emitting devices (OLEDs) with great performance. In this work, four π-shape bipolar host materials, GHA1-4 were designed and synthesized using dibenzofuran core. These hosts exhibit high triplet energy levels as well as excellent thermal stability. Green top-emission OLEDs with GHA1-4 as hosts and Ir (ppy)3 as emitter exhibited excellent performance with high external quantum efficiency (EQEmax) values of above 40%. In addition, devices incorporating GHA1 and GHA3 exhibit a low turn on voltage of 2.07 V, EQEmax of 45.0% and long LT95 device lifetime of 184 h, as well as remarkably small roll-off of only 2.5% at the brightness of 10,000 cd/m2.

Quantum information science is driving progress in a vast number of scientific and technological areas that cover molecular spectroscopy and matter-light interactions in general. In these fields, the ability to generate quantum mechanically-entangled photons is opening avenues to explore the interaction of molecules with quantum light. This work considers an alternative way of correlating photons by including energy superpositions. We study how the multichromatic quantum superposition, or color superposition of photon-pair states, influences the optical properties of organic chromophores. This work uses electronic structure calculations based on time-dependent density functional theory, and a simple modification of the standard entangled two-photon absorption theory. Our calculations show that it is possible to substantially modify the optical absorption cross section of molecules, where constructive and destructive interferences are computed. The quantum interference effects are more pronounced than the constructive ones. These quantum effects, or related ones, could be observed in quantum spectroscopic experiments where qudit photon states are generated.

In organic solar cells (OSCs), it is very important to investigate the relationship between the structure and performance of materials by rational design of small molecule donors (SMDs). In this work, we use thiazole replace a thiophene unit in the π bridge, which could strengthen the connection between π bridges and end groups (EGs). Due to the N–S non-covalent interaction between EG and thiazole unit, the negative charge region of SMDs is expanded, the electron-withdrawing ability of EGs is also enhanced, and the corresponding molecular framework is twisted into a unique linear type. This can effectively enhance intermolecular interaction, promote molecular crystallization, and help to improve hole mobility of related SMDs. This work enriches design strategy that strengthens the interaction between π bridges and EGs, and provides a reference for studying the relationship between molecular structure and crystallinity.

Ultrasonic nebulization is explored here as a resourceful technique for ultrathin film production technique for small molecules. The method can be employed over a variety of substrates, particularly with low viscosity solvents such as water. Specifically for water, spin coating is nearly prohibitive for molecules with a molecular weight up to 1 kDa. However, there is a lack of quantitative results on the ultrasonic nebulization technique when used for deposition in mild conditions that result in film growth. In this work, we study this growth technique to produce ultrathin films of perylenetetracarboxylate derivatives over silica and hexagonal boron nitride flakes. The morphology and physical characteristics of our films were evaluated using atomic force microscopy (AFM) and photoluminescence (PL). A physicochemical model is proposed to explain the overall shape of the height distribution of the films as exponentially-modified Gaussian functions.

A novel approach for improving reproducibility of Organic Field-Effect Transistors electrical performances is proposed. The introduction of isotropic features in the layout of source and drain electrodes is employed to minimize the impact of randomly-distributed crystalline domains in the organic semiconductor film on the reproducibility of basic electrical parameters, such as threshold voltage and charge carrier mobility. A significant reduction of the standard deviation of these parameters is reported over a statistically-relevant set of devices with drop-casted semiconductor, if compared with results obtained in a standard, interdigitated transistor structure. A correlation between electrodes patterning and proposed result is demonstrated by deepening the analysis with the contribution of meniscus-assisted semiconductor printing, in order to precisely control the growth direction of crystals.

This paper demonstrates the designing of π-conjugated donor small organic molecule 4,7-bis(5-((E)-3,5-dimethoxystyryl)thiophen-2-yl)benzo[c][1,2,5]thiadiazole (BTD-2OMe) and its synthesis through the multistep synthetic routes from commercially available low cost precursor materials. The π-conjugated thiophene units interconnected with vinylene in BTD-2OMe favor the red shift absorption spectrum. Thermogravimetric (TGA) and differential scanning calorimetry (DSC) analysis of BTD-2OMe present excellent thermal stability up to ∼403 °C with only 3% weight loss and good crystallization of organic chromophore, respectively. The absorption band in solid state shows the red shift due to J-aggregation and a moderate optical bandgap of ∼1.81 eV with HOMO-LUMO energy levels of −5.35 and −3.54 eV has been obtained. The bulk heterojunction organic solar devices (BHJ-OSCs) have been fabricated and are systematically investigated with different BTD-2OMe:PC71BM (1:1, 1:2, and 1:3, w/w) active layers. The optimized BTD-2OMe:PC71BM (1:2, w/w) device with improved active layer morphology and balanced energy level alignment achieves a high short circuit current density (Jsc) of ∼13.13 mAcm−2 and open-circuit voltage (Voc) of ∼0.924 V resulting in power conversion efficiency (PCE) of ∼6.72%. Importantly, the optimized BTD-2OMePC71BM (1:2, w/w) device poses significantly high device stability of up to 15 days under ambient temperature by retaining ∼95% of PCE from its initial value.

Flexible organic field-effect transistors (FOFETs) have been receiving wide attention for their high flexibility, tunable electronic behavior, and easy integration with flexible devices, and show extensive application potential in the fields of bendable display, flexible sensing, flexible circuits, etc. The formation process of the active layer in the FOFET greatly affects the device's performance. However, effective crystalline growth manipulation of active materials with high carrier mobility remains challenging, especially for the scalable fabrication process of FOFETs. Herein, a sheath gas-assisted direct writing is proposed for the first time to improve the crystal arrangement of ultrathin poly(3-hexylthiophene) (P3HT) films, realized by a combined effect of rheological shearing and drag shearing from sheath gas flow and substrate movement. A coaxial nozzle is designed with the inner channel for P3HT solution, and the sheath gas goes through the outer channel to assist solution deposition onto the substrate. The inlet gas pressure and the moving speed of the substrate are optimized to achieve higher carrier mobility in the active layer. A prototype FOFET was fabricated with a direct-written thin ionic gel film as the dielectric layer. The resulting carrier mobility reached up to 2.527 ± 1.194 cm2/(V·s), and the operating voltage was less than −1.5 V, the device has bendable capability. The FOFET devices were integrated with a flexible humidity sensor and pressure sensors for health monitoring and ON/OFF switch circuits, demonstrating their functions of signal conversion and amplification. This fabrication technique provides an effective mass manufacturing method for FOFETs, and also can be further adapted for crystallization process control in other materials.

Water is known to be the main cause of operational instability in organic electronic devices under ambient conditions. The water-induced hysteresis of lithography-friendly bottom-gate-bottom-contact-type organic field-effect transistors (FETs) with a laminated single-crystal channel was investigated using varying electrode thicknesses. As the amount of water in the air gap enveloped by the semiconductor layer and insulating substrate, adjacent to the electrode, increases, the mechanism dominating the hysteresis phenomenon shifted in the following order: (1) current increase owing to the decreasing charge-injection barrier because of a drain-induced change in the electrode work function, (2) current decrease because of the gate bias stress, and (3) current increase because of the gate enhancement effect owing to the dipole orientation of the water molecules penetrating the semiconductor-insulator interface. Changes in the electrode thickness had the same effect on the hysteretic behavior as the relative humidity of the experimental environment. Thus, this study provides a comprehensive understanding of the water-induced operational instability of laminated organic single-crystal FETs and should aid the realization of stable-operation organic devices, as well as foreign-molecule sensors, by controlling the electrode thickness.

Solid-state LEC exhibits benefits of the simple structure, easy fabrication procedure, and compatibility with air-stable electrodes. Even with the low cost and easy accessibility, organic small molecule ions are not well known for their excellent electroluminescence in LECs. In this design strategy, we have chosen electron-rich triphenylamine and coupled it with thenil imidazole and phenanthroimidazole from both sides with an alkyl chain substitution at N1 position of the imidazole group to construct active material for non-doped LECs. Detailed systematic investigations on optical, electrochemical, thermal, and electroluminescence properties were carried out. For the fabrication of white LECs for lighting applications, the lack of excellent blue LECs has remained a formidable challenge. Herein, our novel ionic small molecule emitters featured bright blue emissions at 479 and 458 nm with the Commission Internationale de I'Eclairage CIE coordinates (0.20, 0.24) and (0.19, 0.22), respectively. It is a remarkable achievement that without a host or extra ions our devices generated eminent blue emissions with a maximum luminance of 899 and 1073 cd m−2 and peak current efficiencies of 1.97 and 2.27 cd A−1. This shows the potential for LECs as low-cost light sources and offers great promise for devices that utilize specifically developed ionic SMs.

The development of molecular magnets plays a major role in emerging organic spintronics applications, as it exhibits both semiconducting and magnetic properties. Herein, we report on the molecular-orientation-dependent magnetic properties of iron phthalocyanine (FePc) thin films and microwires. FePc thin films grown on SiO2 and flexible kapton substrates clearly reveal that the morphology is strongly influenced by the substrates and film thickness. Meanwhile, the molecular stacking orientation of FePc thin films can be tuned by 3, 4, 9, 10-perylenetetracarboxylic dianhydride (PTCDA) templating layer and film thickness. Magnetic hysteresis loops show that the iron atoms are strongly magnetically coupled into ferromagnetic chains at low temperature with high coercivity at 1000 Oe. The magnetization and susceptibility of FePc thin films are dependent on the molecular orientation, and the Curie–Weiss constant is modulated from 24 ± 2 K to 35 ± 2 K through the templating effect, in which the molecular stacking orientation changes from standing-up to lying-down arrangement. Furthermore, strong orientation dependent ferromagnetism is also observed in low-dimensional η-FePc microwires, in which the Curie–Weiss constants change from 20 ± 2 K to 35 ± 2 K when magnetic field rotated from short wire axis to long wire axis. The ability to fabricate FePc thin films on flexible substrate with controllable molecular orientation and ferromagnetism makes them promising candidates for flexible spintronic devices.

The spectrum of the light emitted by a microcavity OLED is strongly time dependent on the nanosecond timescale after switch-on of the pump mechanism. This is one reason why convincing confirmation of laser operation in such device is difficult. The simple theory here presented is helpful in interpreting observed light-emission behavior. One important finding is that the occurrence in the optical spectrum of a narrow Lorentzian on top of a spontaneous-emission pedestal is no guarantee for observed laser operation. Another finding is that reabsorption by the singlet excitons leads to the highest gain when the cavity is detuned to the red side of the emission spectrum. This is confirmed by experimental observations on an optically pumped organic laser diode.

Aqueous electrolyte-gated polymer transistors attracted intensive attention in the field of implantable bionics and biochemical sensors due to their simple fabrication process, low operating voltage, and biocompatibility of salt-in-water. In these devices, under gate bias, the free cations and anions in the water solution gate will drift toward the gate electrode or electrolyte/active layer interface, respectively. Under high enough bias, some ions might insert into the active layer and dope the polymer in electrochemical transistors. Therefore, the ions play a crucial role in the salt-in-water electrolyte-gated polymer electrochemical transistors. In this work, the poly (3-hexylthiophene-2, 5-diyl) (P3HT) electrochemical transistors based on different cations and anions contained in the aqueous electrolytes were characterized. The various measurements imply that the larger perchlorate ions can penetrate the P3HT film much more heavily than the smaller chloride ions and the electrochemical bulk doping occurs in the perchlorate devices while the chloride devices involve surface doping. This is why the perchlorate ions can electrochemically dope the P3HT film more heavily than the chloride ions, leading to the larger transconductance and switching ratio. The various anions show different electrochemical doping processes, leading to various electrical hysteresis characteristics. In addition, the cations can affect the doping relaxation process for the electrochemical transistors. Both cation and anion effects on the device performance and doping/dedoping processes have been investigated in this work.

Impedance spectroscopy was used to investigate the charge transportation and accumulation mechanisms in a mixed-host emissive layer (EML) of phosphorescent organic light-emitting diodes (OLEDs). 1, 3, 5-tris(1-phenyl-1H-benzimidazole-2-yl)benzene (TPBi) and 4, 4′, 4″-tris(N-carbazolyl)-triphenylamine (TCTA) materials were used as the electron transport and hole transport layers, respectively, to fabricate the mixed-host EML device. The results showed enhanced current and power efficiency owing to the use of the same material as the mixed-host EML, eliminating energy barriers within the device, coupled with the negative interfacial charges in the polarized TPBi material. The hole- and electron-split devices of the mixed-host EML OLED were analyzed to comprehensively understand the enhanced electrical properties within the device. Subsequently, the capacitance-frequency (C–F) characteristics of the devices were simulated with an equivalent circuit to quantitatively determine the capacitance and resistance in each organic layer at specific voltages (0–4 V) representing each characteristic step on the capacitance-voltage (C–V) curve.

In this study, we investigated the fabrication of high-performance inverted ternary organic solar cells (OSCs) using solution-processed SnO2 as the electron transport layer. Compared with standard structured OSCs using poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) and LiF, the inverted PM6:PC71BM:Y6-based ternary OSCs showed enhanced charge transport and suppressed charge recombination properties, which are beneficial for improving the solar performance. As a result, an average power-conversion-efficiency (PCE) of 16.3% was achieved for the inverted OSCs using SnO2, which is higher than that (15.2%) of standard devices. Moreover, the inverted OSCs showed a simultaneously improved long-term stability with the PCE degradation significantly suppressed from 46.1% to 23.9% after a 15-days measurement in ambient condition. The best inverted OSC exhibited a highest PCE of 16.7% with a stable power output and negligible hysteresis. Our results demonstrate the superior effect of inverted strategy on boosting the performance of ternary OSCs.

Titanium oxide (TiO2) and tin oxide (SnO2) are the most commonly used electron transport materials for high-efficiency n-i-p perovskite solar cells (PSCs); however, several limiting properties of TiO2 and SnO2 adversely affect device performance. This study describes a facile method to synthesize SnO2:TiO2 hybrid nanocrystals (NCs) to construct electron transport layers (ETLs) with the advantageous properties of both SnO2 and TiO2 for n-i-p PSCs. The optimized SnO2:TiO2 ETL exhibited better surface morphology, well-matched band alignment, higher direct current conductivity, and enhanced electron extraction and transport compared to pristine TiO2 and SnO2 ETLs. Moreover, perovskite films deposited on SnO2:TiO2 ETLs exhibited a higher crystallinity and lower trap-state density than those on TiO2 or SnO2 ETLs. Therefore, SnO2:TiO2-based devices showed high performance (with a power conversion efficiency of 23.19%) and stability (with more than 83% retention of the initial efficiency after 800 h of continuous illumination). This study provides a new method for developing low-cost and efficient ETLs for n-i-p PSCs and confirms that constructing SnO2:TiO2 hybrid ETL is an effective method to fabricate high-efficiency and stable planar perovskite solar cells.

Carrageenan material, which is extracted from red edible seaweed, has been widely used in the food and other industries as a thickener and stabilizer. In this paper, carrageenan is employed for the first time as a resistive memory device structure for both the resistive layer and substrate. The carrageenan substrate (CS) has the advantages of excellent optical transparency, low cost, abundant sources, being skin friendly, and biodegradability. Owing to the excellent bending ability of the CS, the In/carrageenan/Ag/CS memory device (ICAC) can fit closely to human skin. The fabricating process for the ICAC device does not involve a vacuum system. The ICAC device shows promising resistive switching behavior with a high ON/OFF ratio of over 106 and a uniform distribution of switching parameters. Furthermore, when carrageenan is used for both the resistive layer and substrate, this produces strong interfacial adhesion. The good matching of metal-insulator-metal (MIM) structures with flexible substrates enhances the strength of the device structure and result in good bending performance. Supported by convincing physical and electrical evidence, the good uniformity and bending performance of the ICAC device may be related to the ability of the Ag ions (from the bottom electrode) to migrate by interacting with the functional groups of the carrageenan and create Ag filaments. Understanding the underlying switching mechanisms of carrageenan memory devices may enable a new design space for transient resistive-switching memory. This demonstration of a skin-inspired biodegradable carrageenan memory device shows great potential for application in wearable biomedical devices, artificial electronic skin, and even implantable electronics in the foreseeable future.

Fluorescent emitters with both high exciton utilization and luminescence efficiency show promising applications in organic light-emitting diodes (OLEDs), especially those with simultaneously aggregation-induced emission (AIE) and thermally activated delayed fluorescence (TADF). In this work, we performed multi-scale simulations to investigate the photophysical properties of the reported red AIDF compounds T-DA-1, C-DA-1, T-DA-2 and C-DA-2, molecules with the same donor-acceptor group but with very different emission wavelengths and photoluminescence quantum yields (ΦPL) due to different connection points. The packing modes of molecules in film are obtained by molecular dynamics (MD) simulations, the crystal structure is given from the experiment, and then the photophysical properties with the consideration of the solid-state effect are studied by using the combined quantum mechanics and molecular mechanics (QM/MM) method. Natural transition orbitals (NTOs), adiabatic singlet-triplet state energy levels, reorganization energies and HR factors are analysed in detail. In addition, radiative and non-radiative transitions as well as inter-system crossing (ISC) and reverse inter-system crossing (RISC) processes are also investigated. Our results indicate that there is an important role of different substitution positions on the photo physical properties of TADF molecules. The trans-arrangement substitutions restrict the geometry variations, hinder the non-radiative energy consumption process, and promote the radiative process of TADF molecules. In addition, the trans-arrangement in the aggregated state has a smaller ΔEST and a larger SOC, which could favorite the RISC process. Last, the films and crystals of the trans-arrangement molecules have stronger π-π stacking, it limit the movement of molecules, which may inhibit the nonradiative deactivation caused by intramolecular torsional and vibrational excited-energy loss. Our work reasonably elucidates the experimental results and highlights the effect of different substitution positions on TADF properties. This could provide a theoretical perspective for designing efficient AIDF molecules.

Because of the simplicity of device integration, high energy efficiency, and the ability to achieve robust neuromorphic calculation, the explore of artificial synaptic devices has attracted extensive attention. In this work, an electronic synaptic organic transistor based on a mixture of p-type polymer and n-type small molecule semiconductor colloids by spin coating was designed to achieve synaptic plasticity. Typical synaptic behavior, including excitatory postsynaptic current and paired-pulse facilitation, is simulated using electrical impulse stimulation. In addition, the transition from short-term plasticity to long-term plasticity were realized by adjusting input pulse operation. More importantly, the logic function of “AND” and “NAND” gate is designed and realized based on the operability of organic transistor pulse modulation. Our work offers a new approach for the exploitation of organic multifunctional neuromorphic electronic devices.

In solution-processed organic light-emitting devices (OLEDs), a polymer interface layer underneath the emission layer is essential to improving the device's performance. The typical polymer is Poly (9-vinylcarbazole) (PVK), which can dramatically increase the device efficiency whereas the mechanisms are not well understood. In this work, we explored the related mechanisms by smart experimental design and measurements. The results reveal that in addition to reducing the hole current density and balancing the carrier distribution, the PVK underneath layer also improves the film morphology and enhances the horizontal orientation of the transition dipole moment of the thermally activated delayed fluorescence (TADF) emitters. Consequently, the device's efficiency and stability are notably increased by about three times. This work provides insights into the origins of improved device performance in solution-processed TADF OLEDs with a polymer underneath layer and also highlights the effect of the underneath layer on the film formation of the solution-processed emission layer.

Perovskite films with few defects play a key role in preparing high-performance perovskite solar cells (PSCs). Here, cesium halides, such as CsCl, CsBr, and CsI, were introduced as a modulator into 1st PbI2 precursor for manipulating the crystallization of perovskite films. By introducing CsI dense homogeneous perovskite films with high crystallinity, preferential orientation, and a pure black perovskite phase were prepared. In addition, the carrier lifetime of perovskite films was significantly increased because of the suppressed nonradiative recombination. Correspondingly, the power conversion efficiency (PCE) of small-area devices using CsI regulation was increased from 17.45 to 20.29%. Furthermore, the device showed excellent stability maintaining 75% of its initial PCE after 350 h of continuous irradiation. This study demonstrates that CsI-added is a reliable way to prepare PSCs for practical applications.