Solution‐Processable Hole‐Generation Layer and Electron‐Transporting Layer: Towards High‐Performance,Alternating‐Current‐Driven,Field‐Induced Polymer Electroluminescent Devices

The effect of solution‐processed p‐type doping of hole‐generation layers (HGLs) and electron‐transporting layer (ETLs) are systematically investigated on the performance of solution‐processable alternating current (AC) field‐induced polymer EL (FIPEL) devices in terms of hole‐generation capability of HGLs and electron‐transporting characteristics of ETLs. A variety of p‐type doping conjugated polymers and a series of solution‐processed electron‐transporting small molecules are employed. It is found that the free hole density in p‐type doping HGLs and electron mobility of solution‐processed ETLs are directly related to the device performance, and that the hole‐transporting characteristics of ETLs also play an important role since holes need to be injected from electrode through ETLs to refill the depleted HGLs in the positive half of the AC cycle. As a result, the best FIPEL device exhibits exceptional performance: a low turn‐on voltage of 12 V, a maximum luminance of 20 500 cd m^?2, a maximum current and power efficiency of 110.7 cd A^?1 and 29.3 lm W^?1. To the best of the authors' knowledge, this is the highest report to date among FIPEL devices driven by AC voltage.     

High Performance Multi‐Level Non‐Volatile Polymer Memory with Solution‐Blended Ferroelectric Polymer/High‐k Insulators for Low Voltage Operation

Polymer ferroelectric‐gate field effect transistors (Fe‐FETs) employing ferroelectric polymer thin films as gate insulators are highly attractive as a next‐generation non‐volatile memory. Furthermore, polymer Fe‐FETs have been recently of interest owing to their capability of storing data in more than 2 states in a single device, that is, they have multi‐level cell (MLC) operation potential for high density data storage. However, among a variety of technological issues of MLC polymer Fe‐FETs, the requirement of high voltage for cell operation is one of the most urgent problems. Here, a low voltage operating MLC polymer Fe‐FET memory with a high dielectric constant (k) ferroelectric polymer insulator is presented. Effective enhancement of capacitance of the ferroelectric gate insulator layer is achieved by a simple binary solution‐blend of a ferroelectric poly(vinylidene fluoride‐co‐trifluoroethylene) (PVDF‐TrFE) (k ≈ 8) with a relaxer high‐k poly(vinylidene‐fluoride–trifluoroethylene–chlorotrifluoroethylene) (PVDF‐TrFE‐CTFE) (k ≈ 18). At optimized conditions, a ferroelectric insulator with a PVDF‐TrFE/PVDF‐TrFE‐CTFE (10/5) blend composition enables the discrete six‐level multi‐state operation of a MLC Fe‐FET at a gate voltage sweep of ±18 V with excellent data retention and endurance of each state of more than 10⁴ s and 120 cycles, respectively.     

Preparation and Memory Performance of a Nanoaggregated Dispersed Red 1‐Functionalized Poly (N‐vinylcarbazole) Film via Solution‐Phase Self‐Assembly

A nanoaggregated dispersed red 1‐grafted poly(N‐vinylcarbazole) (abbreviated PVDR) is self‐assembled via π–π stacking interactions of the carbazole groups in the polymer system after adding a solution of PVDR in N,N‐dimethylformamide to dichloromethane. Upon self‐assembly, the nanoaggregated PVDR film displays helical columnar stacks with large grain sizes, whereas a non‐aggregated PVDR film exhibits an amorphous morphology with smaller grain size. A write‐once read‐many‐times (WORM) memory device is shown whereby a pre‐assembled solution of PVDR is spin‐coated as the active layer and is sandwiched between an aluminum electrode and an indium‐tin‐oxide (ITO) electrode. This device shows very good memory performance, with an ON/OFF current ratio of more than 10⁵ and a low misreading rate through the precise control of the ON and OFF states. The stability of the nanoaggregated PVDR device is much higher than that of the non‐nanoaggregated PVDR device. This difference in device stability under constant voltage stress can be mainly attributed to the difference in the film crystallinity and surface morphology. No degradation in current density was observed for the ON‐ and OFF‐states after more than one hundred million (10⁸) continuous read cycles indicating that both states were insensitive to the read cycles. These results render the nanoaggregated PVDR polymer as promising components for high‐performance polymer memory devices.     

White Electroluminescence from a Single‐Polymer System with Simultaneous Two‐Color Emission: Polyfluorene Blue Host and Side‐Chain‐Located Orange Dopant

Four single polymers with two kinds of attachment of orange chromophore to blue polymer host for white electroluminescence (EL) were designed. The effect of the side‐chain attachment and main‐chain attachment on the EL efficiencies of the resulting polymers was compared. The side‐chain‐type single polymers are found to exhibit more efficient white EL than that of the main‐chain‐type single polymers. Based on the side‐chain‐type white single polymer with 4‐(4‐alkyloxy‐phenyl)‐7‐(4‐diphenylamino‐phenyl)‐2,1,3‐benzothiadiazoles as the orange‐dopant unit and polyfluorene as the blue polymer host, white EL with simultaneous orange (λ_max = 545 nm) and blue emission (λ_max = 432 nm/460 nm) is realised. A single‐layer device (indium tin oxide/poly(3,4‐ethylenedioxythiophene)/polymer/Ca/Al) made of these polymers emits white light with the Commission Internationale de l'Éclairage coordinates of (0.30,0.40), possesses a turn‐on voltage of 3.5 V, luminous efficiency of 10.66 cd A^–1, power efficiency of 6.68 lm W^–1, and a maximum brightness of 21 240 cd m^–2.     

Alternating‐Current MXene Polymer Light‐Emitting Diodes

MXenes (Ti₃C₂) are 2D transition‐metal carbides and carbonitrides with high conductivity and optical transparency. However, transparent MXene electrodes suitable for polymer light‐emitting diodes (PLEDs) have rarely been demonstrated. With the discovery of the excellent electrical stability of MXene under an alternating current (AC), herein, PLEDs that employ MXene electrodes and exhibit high performance under AC operation (AC MXene PLEDs) are presented. The PLED exhibits a turn‐on voltage, current efficiency, and brightness of 2.1 V, 7 cd A^?1, and 12 547 cd m^?2, respectively, when operated under AC with a frequency of 1 kHz. The results indicate that the undesirable electric breakdown associated with heat arising from the poor interface of the MXene with a hole transport layer in the direct‐current mode is efficiently suppressed by the transient injection of carriers accompanied by the alternating change of the electric polarity under the AC, giving rise to reliable light emission with a high efficiency. The solution‐processable MXene electrode can be readily fabricated on a flexible polymer substrate, allowing for the development of a mechanically flexible AC MXene PLED with a higher performance than flexible PLEDs employing solution‐processed nanomaterial‐based electrodes such as carbon nanotubes, reduced graphene oxide, and Ag nanowires.     

Low Voltage and Ferroelectric 2D Electron Devices Using Lead‐Free BaxSr1‐xTiO3 and MoS2 Channel

Coupling between non‐toxic lead‐free high‐k materials and 2D semiconductors is achieved to develop low voltage field effect transistors (FETs) and ferroelectric non‐volatile memory transistors as well. In fact, low voltage switching ferroelectric memory devices are extremely rare in 2D electronics. Now, both low voltage operation and ferroelectric memory function have been successfully demonstrated in 2D‐like thin MoS₂ channel FET with lead‐free high‐k dielectric Ba_xSr_1‐xTiO₃ (BST) oxides. When the BST surface is coated with a 5.5‐nm‐ultrathin poly(methyl methacrylate) (PMMA)‐brush for improved roughness, the MoS₂ FET with BST (x = 0.5) dielectric results in an extremely low voltage operation at 0.5 V. Moreover, the BST with an increased Ba composition (x = 0.8) induces quite good ferroelectric memory properties despite the existence of the ultrathin PMMA layer, well switching the MoS₂ FET channel states in a non‐volatile manner with a ±3 V low voltage pulse. Since the employed high‐k dielectric and ferroelectric oxides are lead‐free in particular, the approaches for applying high‐k BST gate oxide for 2D MoS₂ FET are not only novel but also practical towards future low voltage nanoelectronics and green technology.     

Printable Ferroelectric PVDF/PMMA Blend Films with Ultralow Roughness for Low Voltage Non‐Volatile Polymer Memory

Here, a facile route to fabricate thin ferroelectric poly(vinylidene fluoride) (PVDF)/poly(methylmethacrylate) (PMMA) blend films with very low surface roughness based on spin‐coating and subsequent melt‐quenching is described. Amorphous PMMA in a blend film effectively retards the rapid crystallization of PVDF upon quenching, giving rise to a thin and flat ferroelectric film with nanometer scale β‐type PVDF crystals. The still, flat interfaces of the blend film with metal electrode and/or an organic semi‐conducting channel layer enable fabrication of a highly reliable ferroelectric capacitor and transistor memory unit operating at voltages as low as 15 V. For instance, with a TIPS‐pentacene single crystal as an active semi‐conducting layer, a flexible ferroelectric field effect transistor shows a clockwise I–V hysteresis with a drain current bistability of 10³ and data retention time of more than 15 h at ±15 V gate voltage. Furthermore, the robust interfacial homogeneity of the ferroelectric film is highly beneficial for transfer printing in which arrays of metal/ferroelectric/metal micro‐capacitors are developed over a large area with well defined edge sharpness.     

Solution‐Processed Highly Efficient Alternating Current‐Driven Field‐Induced Polymer Electroluminescent Devices Employing High‐k Relaxor Ferroelectric Polymer Dielectric

Organic thin‐film electroluminescent (EL) devices, such as organic light‐emitting diodes (OLEDs), typically operate using constant voltage or direct current (DC) power sources. Such approaches require power converters (introducing power losses) and make devices sensitive to dimensional variations that lead to run away currents at imperfections. Devices driven by time‐dependent voltages or alternating current (AC) may offer an alternative to standard OLED technologies. However, very little is known about how this might translate into overall performance of such devices. Here, a solution‐processed route to creating highly efficient AC field‐induced polymer EL (FIPEL) devices is demonstrated. Such solution‐processed FIPEL devices show maximum luminance, current efficiency, and power efficiency of 3000 cd m^?2, 15.8 cd A^?1, and 3.1 lm W^?1 for blue emission, 13 800 cd m^?2, 76.4 cd A^?1, and 17.1 lm W^?1 for green emission, and 1600 cd m^?2, 8.8 cd A^?1, and 1.8 lm W^?1 for orange‐red emission. The high luminance and efficiency, and solution process pave the way to industrial roll‐to‐roll manufacturing of solid state lighting and display.     

Fully Transparent Non‐volatile Memory Thin‐Film Transistors Using an Organic Ferroelectric and Oxide Semiconductor Below 200 °C

A fully transparent non‐volatile memory thin‐film transistor (T‐MTFT) is demonstrated. The gate stack is composed of organic ferroelectric poly(vinylidene fluoride‐trifluoroethylene) [P(VDF‐TrFE)] and oxide semiconducting Al‐Zn‐Sn‐O (AZTO) layers, in which thin Al₂O₃ is introduced between two layers. All the fabrication processes are performed below 200 °C on the glass substrate. The transmittance of the fabricated device was more than 90% at the wavelength of 550 nm. The memory window obtained in the T‐MTFT was 7.5 V with a gate voltage sweep of ?10 to 10 V, and it was still 1.8 V even with a lower voltage sweep of ?6 to 6 V. The field‐effect mobility, subthreshold swing, on/off ratio, and gate leakage currents were obtained to be 32.2 cm² V^?1 s^?1, 0.45 V decade^?1, 10⁸, and 10^?13 A, respectively. All these characteristics correspond to the best performances among all types of non‐volatile memory transistors reported so far, although the programming speed and retention time should be more improved.     

Control of Current Hysteresis of Networked Single‐Walled Carbon Nanotube Transistors by a Ferroelectric Polymer Gate Insulator

Films made of 2D networks of single‐walled carbon nanotubes (SWNTs) are one of the most promising active‐channel materials for field‐effect transistors (FETs) and have a variety of flexible electronic applications, ranging from biological and chemical sensors to high‐speed switching devices. Challenges, however, still remain due to the current hysteresis of SWNT‐containing FETs, which has hindered further development. A new and robust method to control the current hysteresis of a SWNT‐network FET is presented, which involves the non‐volatile polarization of a ferroelectric poly(vinylidene fluoride‐trifluoroethylene) (P(VDF‐TrFE)) gate insulator. A top‐gate FET with a solution‐processed SWNT‐network exhibits significant suppression of the hysteresis when the gate‐voltage sweep is greater than the coercive field of the ferroelectric polymer layer (≈50 MV m^?1). These near‐hysteresis‐free characteristics are believed to be due to the characteristic hysteresis of the P(VDF‐TrFE), resulting from its non‐volatile polarization, which makes effective compensation for the current hysteresis of the SWNT‐network FETs. The onset voltage for hysteresis‐minimized operation is able to be tuned simply by controlling the thickness of the ferroelectric film, which opens the possibility of operating hysteresis‐free devices with gate voltages down to a few volts.     

White Electroluminescence from a Single‐Polymer System with Simultaneous Two‐Color Emission: Polyfluorene as the Blue Host and a 2,1,3‐Benzothiadiazole Derivative as the Orange Dopant

New single‐polymer electroluminescent systems containing two individual emission species—polyfluorenes as a blue host and 2,1,3‐benzothiadiazole derivative units as an orange dopant on the main chain—have been designed and synthesized. The resulting single polymers are found to have highly efficient white electroluminescence with simultaneous blue (λ_max = 421 nm/445 nm) and orange emission (λ_max = 564 nm) from the corresponding emitting species. The influence of the photoluminescence (PL) efficiencies of both the blue and orange species on the electroluminescence (EL) efficiencies of white polymer light‐emitting diodes (PLEDs) based on the single‐polymer systems has been investigated. The introduction of the highly efficient 4,7‐bis(4‐(N‐phenyl‐N‐(4‐methylphenyl)amino)phenyl)‐2,1,3‐benzothiadiazole unit to the main chain of polyfluorene provides significant improvement in EL efficiency. For a single‐layer device fabricated in air (indium tin oxide/poly(3,4‐ethylenedioxythiophene): poly(styrene sulfonic acid/polymer/Ca/Al), pure‐white electroluminescence with Commission Internationale de l'Eclairage (CIE) coordinates of (0.35,0.32), maximum brightness of 12 300 cd m^–2, luminance efficiency of 7.30 cd A^–1, and power efficiency of 3.34 lm W^–1 can be obtained. This device is approximately two times more efficient than that utilizing a single polyfluorene containing 1,8‐naphthalimide moieties, and shows remarkable improvement over the corresponding blend systems in terms of efficiency and color stability. Thermal treatment of the single‐layer device before cathode deposition leads to the further improvement of the device performance, with CIE coordinates of (0.35,0.34), turn‐on voltage of 3.5 V, luminance efficiency of 8.99 cd A^–1, power efficiency of 5.75 lm W^–1, external quantum efficiency of 3.8 %, and maximum brightness of 12 680 cd m^–2. This performance is roughly comparable to that of white organic light‐emitting diodes (WOLEDs) with multilayer device structures and complicated fabrication processes.     

Flash‐Memory Effect for Polyfluorenes with On‐Chain Iridium(III) Complexes

Polyfluorenes containing Ir(III ) complexes in the main chain are demonstrated to have promising application in a polymer memory device. A flash‐memory device is shown whereby a polymer solution is spin‐coated as the active layer and is sandwiched between an aluminum electrode and an indium tin oxide electrode. This device exhibits very good memory performance, such as low reading, writing, and erasing voltages and a high ON/OFF current ratio of more than 10⁵. Both ON and OFF states are stable under a constant voltage stress of ?1.0 V and survive up to 10⁸ read cycles at a read voltage of ?1.0 V. Charge transfer and traps in polymers are probably responsible for the conductance‐switching behavior and the memory effect. The fluorene moieties act as an electron donor and Ir(III ) complex units as the electron acceptor. Furthermore, through the modification of ligand structures of Ir(III ) complex units, the resulting polymers also exhibit excellent memory behavior. Alteration of ligands can change the threshold voltage of the device. Hence, conjugated polymers containing Ir(III ) complexes, which have been successfully applied in light‐emitting devices, show very promising application in polymer memory devices.     

Non‐linear charge conduction and emission behaviour of OELD fabricated with Alq3 and TPD‐doped soluble polyimide

We have attempted to investigate the non‐linear behaviour in the characteristics of organic electroluminescent devices (OELDs) fabricated with polyimide and an organometallic complex as a hole transport layer (HTL) and an emission layer, respectively. The thickness of the polyimide HTL and the kind of metal cathode were varied to study the mechanism of the charge conduction and the electroluminescence (EL). The conventional linear models well explained the voltage‐dependent charge injection and the current‐dependent EL. New non‐linear models proposed here predicted the characteristics almost completely, even though the physical meaning of the included parameters was not clearly defined. The OELD with the Mg cathode showed lower luminous efficiency in the high electric field than that with the Al cathode because of poor adhesion between Mg and Alq3. The maximum luminous efficiency was ca. 1.2 lm/W at 700 cd/m² in the case of the Al cathode. The emission colour did not change for the OELD with the Mg cathode irrespective of the polyimide HTL, whereas the OELD with the Al cathode and the thick HTL showed a red‐shifted EL of ca. 10 nm. Copyright © 2000 John Wiley & Sons, Ltd.     

Self‐Powered Trace Memorization by Conjunction of Contact‐Electrification and Ferroelectricity

Triboelectric nanogenerator (TENG) is a newly invented technology that can effectively harvest ambient mechanical energy from various motions with promising applications in portable electronics, self‐powered sensor networks, etc. Here, by coupling TENG and a thin film of ferroelectric polymer, a new application is designed for TENG as a self‐powered memory system for recording a mechanical displacement/trace. The output voltage produced by the TENG during motion can polarize the dipole moments in the ferroelectric thin film. Later, by applying a displacement current measurement to detect the polarization density in the ferroelectric film, the motion information of the TENG can be directly read. The sliding TENG and the single‐electrode TENG matrix are both utilized for realizing the memorization of the motion trace in one‐dimensional and two‐dimensional space, respectively. Currently, the ferroelectric thin film with a size of 3.1 mm² can record a minimum area changing of 30 mm² and such resolution can still be possibly improved. These results prove that the ferroelectric polymer is an effective memory material to work together with TENG and thereby the fabricated memory system can potentially be used as a self‐powered displacement monitor.     

A Series of Energy‐Transfer Copolymers Derived from Fluorene and 4,7‐Dithienylbenzotriazole for High Efficiency Yellow,Orange, and White Light‐Emitting Diodes

Eight random and alternating copolymers PF‐DTBTA derived from 2,7‐fluorene and 4,7‐dithienylbenzotriazole (DTBTA) were synthesized. Thin solid films of the energy‐transfer copolymers possess high absolute photoluminescence (PL) quantum yields (Φ_PL) between 60?72%. Inserting PVK layer between anode and emissive layer could show higher electroluminescence (EL) performances due to PVK‐enhanced hole injection. Random copolymers PF‐DTBTA1?15, with DTBTA molar contents from 1% to 15%, displayed yellow EL spectra with high external quantum efficiency (EQE_max) up to 5.78%. PF‐DTBTA50, the alternating copolymer, showed an orange EL with EQE_max of 3.3%. The good Φ_PL and EQE_max of the PF‐DTBTA50 with very high DTBTA content indicate that DTBTA is a high efficiency chromophore with very low concentration quenching effects in the solid state PL and EL processes. PF‐DTBTA0.03?0.1 could emit white EL due to partial energy transfer from fluorene segments to DTBTA units. Moreover, white EL devices, with forward‐viewing maximum luminous efficiency up to 11 cd/A and stable white EL spectra (CIE coordinates of (0.33, 0.43)) in high current range from 5 mA to 60 mA, could be realized from the non‐doped polymer with simple binary structure. Our results suggest that DTBTA has big potential to construct high performanced EL polymers or oligomers.     

Cover Picture: White Electroluminescence from a Single‐Polymer System with Simultaneous Two‐Color Emission: Polyfluorene as the Blue Host and a 2,1,3‐Benzothiadiazole Derivative as the Orange Dopant (Adv. Funct. Mater. 7/2006)

New single‐polymer electroluminescent systems containing two individual emission species—polyfluorenes as a blue host and 2,1,3‐benzothiadiazole derivative units as an orange dopant on the main chain—have been designed and synthesized by Wang and co‐workers on p. 957. The resulting single polymers are found to have highly efficient white electroluminescence with simultaneous blue and orange emission from the corresponding emitting species. A single‐layer device has been fabricated that has performance characteristics roughly comparable to those of organic white‐light‐emitting diodes with multilayer device structures. New single‐polymer electroluminescent systems containing two individual emission species—polyfluorenes as a blue host and 2,1,3‐benzothiadiazole derivative units as an orange dopant on the main chain—have been designed and synthesized. The resulting single polymers are found to have highly efficient white electroluminescence with simultaneous blue (λ_max = 421 nm/445 nm) and orange emission (λ_max = 564 nm) from the corresponding emitting species. The influence of the photoluminescence (PL) efficiencies of both the blue and orange species on the electroluminescence (EL) efficiencies of white polymer light‐emitting diodes (PLEDs) based on the single‐polymer systems has been investigated. The introduction of the highly efficient 4,7‐bis(4‐(N‐phenyl‐N‐(4‐methylphenyl)amino)phenyl)‐2,1,3‐benzothiadiazole unit to the main chain of polyfluorene provides significant improvement in EL efficiency. For a single‐layer device fabricated in air (indium tin oxide/poly(3,4‐ethylenedioxythiophene): poly(styrene sulfonic acid/polymer/Ca/Al), pure‐white electroluminescence with Commission Internationale de l'Eclairage (CIE) coordinates of (0.35,0.32), maximum brightness of 12 300 cd m^–2, luminance efficiency of 7.30 cd A^–1, and power efficiency of 3.34 lm W^–1 can be obtained. This device is approximately two times more efficient than that utilizing a single polyfluorene containing 1,8‐naphthalimide moieties, and shows remarkable improvement over the corresponding blend systems in terms of efficiency and color stability. Thermal treatment of the single‐layer device before cathode deposition leads to the further improvement of the device performance, with CIE coordinates of (0.35,0.34), turn‐on voltage of 3.5 V, luminance efficiency of 8.99 cd A^–1, power efficiency of 5.75 lm W^–1, external quantum efficiency of 3.8 %, and maximum brightness of 12 680 cd m^–2. This performance is roughly comparable to that of white organic light‐emitting diodes (WOLEDs) with multilayer device structures and complicated fabrication processes.     

聚合物电致发光器件中用类金刚石碳膜增强电子注入

用正丁胺作碳源,采用射频辉光等离子系统制备类金刚石碳膜(DLC),沉积在聚合物发光器件中的发光层(MEH-PPV)和铝(Al)阴极间作电子注入层.制备了结构为ITO/MEH-PPV/DLC/Al的不同DLC厚度的器件,测量了器件的I-V特性、亮度及效率,研究了DLC层对器件电子注入性能影响的机制.结果表明:当DLC厚度小于1.0nm时,其器件有较ITO/MEH-PPV/Al高的启动电压和低的发光效率;当DLC厚度在1.0～5.0nm之间时,器件的性能随着DLC厚度增加而变好;当DLC厚度为5.0nm时,器件具有最低的启动电压与最高的发光效率;当DLC厚度继续增加时,器件的性能随着DLC厚度增加而变差.并对ITO/MEH-PPV/DLC/Al和ITO/MEH-PPV/LiF/Al的器件性能进行了比较研究.     

A Semi‐Floating Memory with 535% Enhancement of Refresh Time by Local Field Modulation

The recently proposed semi‐floating gate memory technology shows the potential to balance conflicts between writing speed and data storage. Although the introduction of the p–n junction greatly improves device writing speed, the inevitable junction leakage limits the further extension of data retention time. A local nonvolatile electric field is introduced by exploiting the polarization of ferroelectric gate dielectric HfZrO₄ to modulate the charge leakage speed of the p–n junction since the carrier density of 2D materials can be efficiently regulated. The refresh time is greatly prolonged more than 535%, solving the bottleneck problem of relatively short retention time of previous semi‐floating gate memory. In addition, the characteristics of device under low operation voltage is also explored, which can serve for further power reducing. This design realizes the combination of ultrafast writing operation and significant enhanced data retention ability, which provides a new idea of the development for high speed non‐volatile memory technology.     

Nonvolatile Ferroelectric P(VDF‐TrFE) Memory Transistors Based on Inkjet‐Printed Organic Semiconductor

Nonvolatile ferroelectric poly(vinylidene fluoride‐co‐trifluoroethylene) memory based on an organic thin‐film transistor with inkjet‐printed dodecyl‐substituted thienylenevinylene‐thiophene copolymer (PC12TV12T) as the active layer is developed. The memory window is 4.5 V with a gate voltage sweep of ?12.5 V to 12.5 V. The field effect mobility, on/off ratio, and gate leakage current are 0.1 cm²/Vs, 10⁵, and 10^?10 A, respectively. Although the retention behaviors should be improved and optimized, the obtained characteristics are very promising for future flexible electronics.     

Non‐volatile Ferroelectric Poly(vinylidene fluoride‐co‐trifluoroethylene) Memory Based on a Single‐Crystalline Tri‐isopropylsilylethynyl Pentacene Field‐Effect Transistor

A new type of nonvolatile ferroelectric poly(vinylidene fluoride‐co‐trifluoroethylene) (P(VDF‐TrFE)) memory based on an organic thin‐film transistor (OTFT) with a single crystal of tri‐isopropylsilylethynyl pentacene (TIPS‐PEN) as the active layer is developed. A bottom‐gate OTFT is fabricated with a thin P(VDF‐TrFE) film gate insulator on which a one‐dimensional ribbon‐type TIPS‐PEN single crystal, grown via a solvent‐exchange method, is positioned between the Au source and drain electrodes. Post‐thermal treatment optimizes the interface between the flat, single‐crystalline ab plane of TIPS‐PEN and the polycrystalline P(VDF‐TrFE) surface with characteristic needle‐like crystalline lamellae. As a consequence, the memory device exhibits a substantially stable source–drain current modulation with an ON/OFF ratio hysteresis greater than 10³, which is superior to a ferroelectric P(VDF‐TrFE) OTFT that has a vacuum‐evaporated pentacene layer. Data retention longer than 5 × 10⁴ s is additionally achieved in ambient conditions by incorporating an interlayer between the gate electrode and P(VDF‐TrFE) thin film. The device is environmentally stable for more than 40 days without additional passivation. The deposition of a seed solution of TIPS‐PEN on the chemically micropatterned surface allows fabrication arrays of TIPS‐PEN single crystals that can be potentially useful for integrated arrays of ferroelectric polymeric TFT memory.