We demonstrate a solution method of volatilize-controlled oriented growth (VOG) to fabricate aligned single crystals of 6,13-bis(triisopropylsilylethynyl) pentacene (TIPS pentacene) on a Si/SiO2 substrate. Through controlling the evaporation rate of the solvent, large-area-aligned single-crystal layers can be achieved on several substrates at the same time, covering over 90% on 2 × 1 cm substrates. The method provides a low-cost, maneuverable technology, which has potential to be used in batch production. We find that the atmosphere of the solvent with high dissolving capacity is in favor of aligned single-crystal growth. Besides, the growth mechanism of the VOG method is investigated in this paper. Top-contact organic field-effect transistors based on the single crystals of TIPS pentacene are achieved on a Si/SiO2 substrate. The optimal device exhibits a field-effect mobility of 0.42 cm2 V–1 s–1 and an on/off current ratio of 105. Our research indicates that the VOG method is promising in single-crystal growth on a Si/SiO2 substrate for commercial production.

Flexible electronics has attracted enormous interest in wearable electronics and human–machine interfacing. Here, a flexible organic tribotronic transistor (FOTT) without a top gate electrode has been demonstrated. The FOTT is fabricated on a flexible polyethylene terephthalate film using the p-type pentacene and poly(methyl methacrylate)/Cytop composites as the conductive channel and dielectric layer, respectively. The charge carriers can be modulated by the contact electrification between the dielectric layer and a mobile triboelectric layer. Based on the fabricated FOTT, pressure and magnetic sensors have been developed, respectively, that exhibit great sensitivity, fast response time, and excellent stability. The FOTT in this simple structure shows bright potentials of tribotronics in human–machine interaction, electronic skins, wearable electronics, intelligent sensing, and so on.Keywords: magnetic sensor; organic tribotronic transistor; pressure sensor; triboelectric nanogenerator; tribotronics;

Organic photodiodes (OPD) are becoming promising candidates for narrowband detection to meet new requirements on detectors, such as smaller size, higher resolution, lower power consumption, and the ability to interact with a variety of interfaces. In this article, a new narrowband green-light sensitive squarylium material with donor–acceptor–donor structure and its application in photodiode are reported. Due to the material with intense and sharp absorption in the green color and simple single-layer structure, the device shows excellent color selectivity. The green EQE of the device reaches 66%, while the blue EQE is as low as 10%. The device also shows significantly low dark current of ∼5.4 nA·cm–2 at −2.5 V and high specific detectivity of 7.7 × 1012 Jones. The strategy for designing narrowband OPD can be extended to other wavelength region by replacing substituent group in the donor–acceptor–donor structure of the squarylium and using the single-layer structure.

•A flexible transparent tribotronic transistor is developed by coupling an OTFT and a TENG.•The FTT has good performances in stability and durability in different bending modes and radius.•The FTT can be used as electronic skin in man-machine interface for active modulation of conventional electronics.Flexible and transparent electronics have attracted wide attention for electronic skin, wearable sensors and man-machine interactive interfacing. In this paper, a novel flexible transparent tribotronic transistor (FTT) is developed by coupling an organic thin film transistor (OTFT) and a triboelectric nanogenerator (TENG) in free-standing sliding mode. The carrier transport between drain and source can be modulated by the sliding-induced electrostatic potential of the TENG instead of the conventional gate voltage. With the sliding distance increases from 0 to 7 mm, the reverse drain current is almost linearly increased from 2 to 22 μA. The FTT has excellent performances in stability and durability in different bending modes and radius. The optical transmittance of the device is about 71.6% in the visible wavelength range from 400 to 800 nm. Moreover, the FTT is used for active modulation of conventional electronics, in which the luminance, magnetism, sound and micro-motion can be modulated by sliding a finger. This work has provided a new way to actively modulate conventional electronics, and demonstrated the practicability of tribotronics for human-machine interaction.A novel flexible transparent tribotronic transistor (FTT) is developed by coupling an organic thin film transistor (OTFT) and a triboelectric nanogenerator (TENG) in free-standing sliding mode. The FTT is used for active modulation of conventional electronics, in which the luminance, magnetism, sound and micro-motion can be modulated by sliding a finger.

•Two narrowband OPDs with good color-selectivity was obtained.•Strategy for selecting materials narrowband absorption was presented.•A multi-user VLC system was developed based on all-organic component without filter.In this paper, based on 1,3-bis[(3,3-dimethylindolin-2-ylidene)methyl]squaraine (ISQ), which has narrowband red-light absorption, and Rubrene, which possesses significant blue-light absorption, two color-selective organic photodetectors (OPDs) are developed. By quantum chemistry calculation, the mechanism of ISQ's sharp absorption spectrum is analyzed. Without input filtering, the two OPDs are well suited for two-channel visible light communications (VLC) system due to their good orthogonality of response spectrum and exceptional features, such as flexibility and ability to realize large-area thin-film manufacturing. With the two OPD as receivers and corresponding organic light emitting diodes (OLEDs) as data transmitters respectively, a two-channel VLC system delivering a bit-rate of 530 kb/s in the blue-light channel and 180 kb/s in the red-light channel was experimentally demonstrated. The two channels have good orthogonality when they operate together. This all-organic VLC system demonstrates the feasibility and benefit for the application of organic electronics in the communication field.

We demonstrate a solution method of Marangoni effect-controlled oriented growth (MOG) to fabricate highly oriented crystals of 6,13-bis(triisopropylsilylethynyl)pentacene (TIPS pentacene) on the Si/SiO2 substrate. Based on the Marangoni effect induced by mixed solvent systems, large area aligned ribbon crystals can be achieved, covering over 60% on 4 cm × 1 cm Si/SiO2 substrates. We investigated the growth mechanism of the MOG method and found that the correct choice of solvents and appropriate solvent ratios are in favor of aligned crystal growth. With the ribbon crystals of TIPS pentacene, top-contact organic field-effect transistors are fabricated. The optimal device exhibits a field-effect mobility of 0.70 ± 0.22 cm2 V−1 s−1 and an on/off ratio of 105. The MOG method, which has potential to be used in batch production and features easy control of crystal growth using non-contact forces, will benefit the development of low-cost, high-performance, organic semiconductor devices.

•Hysteresis in perovskite devices results from dynamic charge trapping–detrapping processes.•Proportion of deep traps to shallow traps differs in planar and in porous device.•A multi-bit organic memory can be a potential application of perovskite devices.The hysteresis in perovskites devices puzzled researchers because it was a big hurdle for device stability and the origin of it was still a riddle for people to solve. Here we reported our analysis in mechanism of the hysteresis based on the trap states in the perovskites film surface. We tried to explain the current hysteresis through the dynamic charge trapping–detrapping processes and the conclusion applied both in porous and planar structure devices. However, the proportion of deep traps and shallow traps are different in planar structure device and in porous structure device. Furthermore, we found perovskite devices has potentials of serving as memory devices due to the photocurrent hysteresis. The on/off ratio of memory based on perovskite can be higher than 60 and the write time was as low as 0.54 s as memory. It also had a very low read bias near 0 V. Moreover, the devices show multi-bit property and a multi-bit organic memory came forward as a novel application of perovskite devices.

•Organic–inorganic hybrid optocouplers with OLED and a-Si:H photodiodes were investigated.•The current density transfer ratio of the optocoupler reaches 10.7%.•The hybrid optocouplers exhibit promising results and can be further improved.•This type of devices can be applied to many solid or flexible optoelctronics.Organic–inorganic hybrid electronics have attracted considerable attention because of the possibility of combining advantages of both the organic and inorganic devices. High-performance hybrid optocouplers made of the a-Si:H pin photodiode and organic light emitting diodes have been fabricated and studied. With a blue organic light emitting diode as the light source, the optocoupler shows good photoresponse with a current transfer ratio of 3.72% at the photodetector bias of −2 V and a large light/dark current ratio of 5.6 × 106. With a high efficiency tandem white organic light emitting diode as the light source, an even higher current transfer ratio of 10.7% was achieved, which is larger than that of the all-organic optocoupler and is comparable to that of the all-inorganic optocoupler. Influences of different wavelength components ratios of the OLED spectrum on the photoresponse of a-Si:H pin photodiode was also investigated. It shows that the selection of OLED wavelength plays important roles in improving the performance of OOC. This kind of organic–inorganic hybrid system can be used in many electronic and optoelectronic products.

An organic phototransistor (OPT) shows nonvolatile memory effect due to its novel optical writing and electrical erasing processes. In this work, we utilize an organic light-emitting diode (OLED) as the light source to investigate OPT-based memory (OPTM) performance. It is found that the OPTM can be used as either flash memory or write-once read-many-times memory by adjusting the properties of the Ta2O5 gate dielectric layer. UV/ozone treatment is applied to effectively change dielectric properties of the Ta2O5 film. The mechanisms for this are examined by X-ray photoelectron spectroscopy and capacitance–voltage measurement. It turns out that the densities of oxygen vacancies and defects in the first 1.8 nm Ta2O5 films near the Ta2O5/semiconductor interface are reduced. Furthermore, for the first time, we use this multifunctional OPTM, which unites the photosensitive and memory properties in one single device, as an optical feedback system to tune the brightness of the OLED. Our study suggests that these OPTMs have potential applications in tuning the brightness uniformity, improving the display quality and prolonging the lifetime of flat panel displays.Keywords: multifunctional applications; nonvolatile memory; organic phototransistor; UV/ozone treatment;

•The photocurrent of OPD was determined by optical field distribution and electric field distribution in OPD simultaneously.•A model for predicting the tendency of photocurrent in OPDs is set up.•Devices built according to the simulated optimal configurations through our model gains improved photocurrents as expected.•A method for estimating the diffusion length of C60 was obtained.Optical field distribution and electric field distribution in organic photodiodes (OPDs) are of great importance for exciton generation and photocurrent improvement. Therefore, the influence of the two factors on the properties of OPDs should be considered simultaneously to get optimal devices. In this research, we analyzed the dependence of the photocurrents of m-MTDATA/C60 heterojunction OPDs on the light absorption and electric field distribution. And then a model was set up for predicting the tendency of photocurrent changing with the thicknesses of devices. The validity of the model was well verified by the consistency of the simulated data and the experimental data. Devices built according to the simulated optimal configurations gained improved photocurrents as expected. Furthermore, based on the model, we also presented a simple method to estimate the diffusion length of C60, which may be suitable for other materials.

•The increasing O2 ratio during the fabrication process improves the OPTM performance.•The oxygen content can alter the roughness and surface energy of Ta2O5 film.•Trap density changes are certificated by KFM and vacuum-ultraviolet spectroscopy.•The oxygen content can modulate the electron trap density in the Ta2O5 film.Optical writing and electrical erasing organic phototransistor memory (OPTM) is a promising photoelectric device for its novel integration of photosensitive and memory properties. The performance of OPTM can be influenced by the trap density of the gate dielectric layer. Here, we occupy tantalum pentoxide (Ta2O5), which is a prospective material in microelectronics field, as the gate dielectric. By increasing the oxygen content from 10% to 50% during the fabrication process of Ta2O5, it is found that the mobility and the photoresponsivity of OPTMs are significantly enhanced about 10 times and the retention time is greatly increased to 8.4 × 104 s as well. As far as we know, this is the first example that the modulation of oxygen content can improve the OPTM performance. Furthermore, the change of the oxygen content gives rise to the alteration of the threshold voltage and memory window, of which the absolute values of all the threshold voltage are below 5 V which is low enough to reduce the power consumption. It is found that the oxygen content can influence the surface roughness and surface energy of Ta2O5 films, which alter the nucleation and orientation of semiconductor layers, change the contact resistance and modulate the electron trap density in the Ta2O5 films.Graphical abstract

We synthesized a new ionic iridium complex with interesting multifunctions of both insulativity and light emission. With this material as gate dielectric, we have fabricated a multifunctional device which behaves as a normal transistor at low gate voltage and a light emitting device when the voltage is over 4 V. The emission brightness can be tuned by VGS and VDS separately. This device can potentially be applied in overvoltage alarm systems.

We demonstrate a solution method of volatilize-controlled oriented growth (VOG) to fabricate aligned single crystals of 6,13-bis(triisopropylsilylethynyl) pentacene (TIPS pentacene) on a Si/SiO2 substrate. Through controlling the evaporation rate of the solvent, large-area-aligned single-crystal layers can be achieved on several substrates at the same time, covering over 90% on 2 × 1 cm substrates. The method provides a low-cost, maneuverable technology, which has potential to be used in batch production. We find that the atmosphere of the solvent with high dissolving capacity is in favor of aligned single-crystal growth. Besides, the growth mechanism of the VOG method is investigated in this paper. Top-contact organic field-effect transistors based on the single crystals of TIPS pentacene are achieved on a Si/SiO2 substrate. The optimal device exhibits a field-effect mobility of 0.42 cm2 V–1 s–1 and an on/off current ratio of 105. Our research indicates that the VOG method is promising in single-crystal growth on a Si/SiO2 substrate for commercial production.

Organic transistors have proved to have potential applications in pressure sensors. However, few reports consider the coactions of pressure and ambient gas adsorption on the characteristics of the sensitive transistors. In this article, pentacene polycrystalline thin films were fabricated as the active layer of organic transistors, and the effects of ambient pressure and the gas adsorption on the carriers’ transport characteristics have been investigated. It was found that during the process from one atmosphere to vacuum (∼5 × 10–3 Pa) the device output, saturation source-drain currents (IDS), changed with pressure not monotonously but with an unexpected reversible minimum peak. Considering the variation of gas adsorption quantity and the distance between pentacene grains with pressure, we established models to understand the nature of the pressure sensitivity. We found that in low pressures the adsorption of gas molecules in grain boundaries was the main factor that affects device performance, whereas in high pressures, the shortening of the distance between pentacene grains was the main factor. Our research will benefit the understanding of charge-transport nature and, more importantly, give some instructions on using and designing highly sensitive pressure sensors.

Low-voltage organic phototransistors (OPTs) are promising for optoelectronic applications such as photosensors and memory. In this paper, pentacene and Ta2O5 were used as the active layer and the gate dielectric, respectively. Commonly used polymer materials, such as poly(4-vinylphenol) and poly(methyl methacrylate), were spin-coated on the high transparency and high permittivity Ta2O5 layer as modification layers. The effects of the interface modification were investigated. It was found that the modification layers can block the electron injection process as the lowest unoccupied molecular orbital levels are higher than that of pentacene, and then reduce photosensitivity and memory effect. However, it was also observed that, for the modified device, the photoresponsivity, photocurrent/dark current ratio and retention time can be improved by modulating the optical writing process through varying a series of gate voltages accompanied by light illumination. Through analysis of energy levels, the mechanism of the tuning is proposed that the polymeric layer acts as a tunneling layer for high-energy electrons and a blocking layer for low-energy electrons. Our study verifies that interface modification benefits not only the OPT performance but also its applications in different fields.

The memory nature and mechanism of the Ta2O5-gate-dielectric-based organic phototransistor memory (OPTM) have been studied. The UV–Vis absorption spectra and the X-ray photoelectron spectroscopy indicate that Ta2O5 owns positive interfacial charge because of the existence of Ta–OH. The hydroxide results in oxygen deficiency in Ta2O5 which is proposed to trap electrons. The characteristics of Ta2O5-based capacitor and the energy level alignment at Ta2O5–pentacene interface reveal that the electron-injection process is favorable which stimulates the electron-trapping process in Ta2O5. The Kelvin probe force microscopy of the Ta2O5-pentacene interface certificates the electron-injection and electron-trapping processes as well. It is the positive charges in Ta2O5 and energy level alignment that lead to the memory effect of Ta2O5-gate-dielectric-based OPTM. Compared to Ta2O5, polymethyl methacrylate (PMMA) does not have so strong a positive interface. Accordingly, PMMA films of different thickness are adopted on Ta2O5 to tune the Ta2O5-pentacene interface, offering control of the memory properties including the memory window and retention time. The understanding of the mechanism is at the forefront of devising high-performance OPTM devices.Graphical abstractHighlights► OPTM is brand new for its optical writing and electrical erasing processes. ► UV–Vis, XPS and KFM have been employed to identify the memory nature and mechanism. ► The positive charge surface of Ta2O5 and the energy level alignment contribute to the memory effect.

We establish quantitative models on the formation of depletion regions in organic photodiodes (OPD) based on fullerene/N,N′-diphenyl-N,N′-bis(1-naphthyl)-1,1′-biphenyl-4,4′-diamine (C60/NPB) heterojunctions. The models describe the relation of dark current and open-circuit voltage to the deposited thickness of C60 or NPB. Interfacial electronic structures, such as built-in potential, the charge density, the minimized thicknesses of completely developed depletion regions and the energy level bending on each side of the heterojunction were derived from the fitting model. Also, we observed a shift of depletion region from NPB to C60 due to the relative change of charge density under illumination. The device performance proved the reasonability of the models. This paper provides a universally applicable method to probe the interfacial information of organic semiconductors.Graphical abstractDark Current and photovoltage models on the formation of depletion region in C60/NPB Organic heterojunctions. The structure of C60/NPB organic photodiode and its dark current and open-circuit voltage vs different semiconductor thicknesses.Highlights► We study the C60/NPB organic heterojunction photodiodes (OPD) by adjusting the thicknesses of semiconductor layers. ► Theoretical models are proposed to numerically fit the dark current and photovoltage of different OPD structures. ► The critical thicknesses of C60/NPB heterojunction are deduced to be 5 nm/70 nm in the dark and 8 nm/60 nm in light. ► Comparison of the performance parameters of C60/NPB OPDs verifies the correctness of the fitting results. ► The finally optimized structure of C60/NPB heterojunction is 8 nm/70 nm.

The measurement of charge mobility is of great importance to optimize the performance of organic semiconductor materials and understand the charge transport behaviors. In this Article, we present a new and in situ method to measure the carrier mobilities in organic semiconductor materials by testing the frequency characteristics of organic optoelectronic coupler (OOC) devices. In this method, a square-wave voltage was applied as the input signal and the mobilities of the related organic semiconductors in the device can be obtained from the falling-edge transient of the output current signal. On the basis of our sample OOC devices of ITO/PEDOT:PSS/C60/(NPB or m-MTDATA)/LiF/Al)/OLED, we successfully achieved the hole mobilities of N,N′-diphenyl-N,N′-bis(1,1′-biphenyl)-4,4′-diamine (NPB) and 4,4′,4″-tris{N,-(3-methylphenyl)-N-phenylamino}triphenylamine (m-MTDATA) to be (1.21 to 2.38) × 10–4 and 4.55 × 10–5 cm2 V–1 s–1, respectively. These results verified the reliability of this new method. Compared with the traditional mobility measurement methods, the new method has advantages of showing the real mobilities in the operating devices and saving materials by decreasing the thickness of semiconductor thin films from micrometers to nanometers.

A series of indolium squarine dyes were studied as air-stable semiconductors in organic field-effect transistors. By modulating substituted groups and structural rigidity, a mobility of 4.8 × 10−3 cm2/Vs was achieved in solution processed device and the highest mobility of 0.2 cm2/Vs was obtained in single crystal devices. By structural analysis and theoretical calculation, crystal packing mode was found to be associated with the electrostatic attraction and repulsion between positive and negative charge centers of the molecule. This electrostatic interaction drove the spontaneous intermolecular ordering in the film, and resulted in performance enhancement for ISQ transistors. Quantitative research between mobility and the area of polycrystalline regions revealed the dependence of transport ability on the continuity and uniformity of the crystalline phase.Graphical abstractThe intermolecular electrostatic interaction and transistor of ISQ compounds.Highlights► We fabricated air-stable field-effect transistors based on a series of indolium squarine dyes. ► Packing configuration in crystal was affected by intermolecular electrostatic interaction. ► Increased device performance was observed accompanied with the crystallization of film after annealing. ► The highest mobility is 0.2 cm2/Vs. ► The morphology and performance could be modulated by the design of side groups.

Organic optocoupler (OOC) or organic photocoupler, optical coupler is a novel and one of the most promising organic optoelectronic devices for its well electrical isolation and anti-jamming ability in long-distance and real-time digital communications. The performance parameters of OOC were greatly raised during the past decade, and its development was strongly associated with basic organic devices such as organic light emitting diodes (OLED), organic photodiodes (OPD) and organic phototransistors (OPT) etc. Here we describe the principles of OOC, review recent breakthroughs in this field, and summarize the photosensor and light emitting parts which could be used in the device. Key technical points, such as current transfer ratio, frequency, matching and stability were also discussed in this paper.

Poly(phenylene sulfide) (PPS) is a well-known organic insulator. However, the PPS thin film, deposited by thermal evaporation in vacuum, showed electrical bistable characteristics. The structure of the PPS thin-film device was glass/ITO/PPS (300 nm)/Au. The thin film can be converted to a high conductance state by applying a pulse of 80 V (5 s), and brought back to a low conductance state by applying a pulse of 100 V (5 s). This kind of thin film is potential for active layer of a memory device. The critical voltage of the device is about 40 V, while the read-out voltage is 5 V. We tentatively ascribe the bistable phenomenon to the charge transfer from S to C atoms in the PPS molecule chains.

•Organic–inorganic hybrid optocouplers with OLED and a-Si:H photodiodes were investigated.•The current density transfer ratio of the optocoupler reaches 10.7%.•The hybrid optocouplers exhibit promising results and can be further improved.•This type of devices can be applied to many solid or flexible optoelctronics.Organic–inorganic hybrid electronics have attracted considerable attention because of the possibility of combining advantages of both the organic and inorganic devices. High-performance hybrid optocouplers made of the a-Si:H pin photodiode and organic light emitting diodes have been fabricated and studied. With a blue organic light emitting diode as the light source, the optocoupler shows good photoresponse with a current transfer ratio of 3.72% at the photodetector bias of −2 V and a large light/dark current ratio of 5.6 × 106. With a high efficiency tandem white organic light emitting diode as the light source, an even higher current transfer ratio of 10.7% was achieved, which is larger than that of the all-organic optocoupler and is comparable to that of the all-inorganic optocoupler. Influences of different wavelength components ratios of the OLED spectrum on the photoresponse of a-Si:H pin photodiode was also investigated. It shows that the selection of OLED wavelength plays important roles in improving the performance of OOC. This kind of organic–inorganic hybrid system can be used in many electronic and optoelectronic products.

We demonstrate a solution method of Marangoni effect-controlled oriented growth (MOG) to fabricate highly oriented crystals of 6,13-bis(triisopropylsilylethynyl)pentacene (TIPS pentacene) on the Si/SiO2 substrate. Based on the Marangoni effect induced by mixed solvent systems, large area aligned ribbon crystals can be achieved, covering over 60% on 4 cm × 1 cm Si/SiO2 substrates. We investigated the growth mechanism of the MOG method and found that the correct choice of solvents and appropriate solvent ratios are in favor of aligned crystal growth. With the ribbon crystals of TIPS pentacene, top-contact organic field-effect transistors are fabricated. The optimal device exhibits a field-effect mobility of 0.70 ± 0.22 cm2 V−1 s−1 and an on/off ratio of 105. The MOG method, which has potential to be used in batch production and features easy control of crystal growth using non-contact forces, will benefit the development of low-cost, high-performance, organic semiconductor devices.