Single-Component CMOS-Like Logic using Diketopyrrolopyrrole-Based Ambipolar Organic Electrochemical Transistors

Complementary circuits based on organic electrochemical transistors (OECTs) are attractive for the development of inexpensive and disposable point-of-care bioelectronic devices. Ambipolar OECTs, which employ a single channel material, could decrease the fabrication complexity and manufacturing costs of such circuits. An ideal channel material for ambipolar OECTs should be electrochemically stable in aqueous environments, afford facile ion insertion for both cations and anions, and also facilitate high and balanced electron and hole transport. In this study, triethylene glycol functionalized diketopyrrolopyrrole (DPP)-based polymer is proposed for the development of ambipolar OECTs. It is shown that DPP-based OECTs have a high and comparable figure of merit for both n- and p-type operations. Logic NOT, NAND, and NOR operations with corresponding complementary circuits constructed from identical DPP-based OECT devices are demonstrated. This study is an important step toward the development of sophisticated complementary metal–oxide–semiconductor-like logic circuits using single-component OECTs.     

Insulating Electrets Converted from Organic Semiconductor for High-Performance Transistors,Memories, and Artificial Synapses

Electrets are commonly used charged insulators that generate a quasi-permanent electric field. However, when conventional electrets come into direct contact with semiconductors, the energy level mismatch at the interface results in low memory speed and high energy consumption of electret devices due to both charge injection and storage being non-conducive. To address this, the n-type semiconductor N,N′-dioctyl-3,4,9,10-perylene tetracarboxylic diimide (C₈-PTCDI) is converted to C₈-PTCDI (D) via oxygen degradation. The resulting C₈-PTCDI (D) electrets, when charged using an electric field and/or light, retain the energy level of the n-type semiconductors to facilitate charge trapping. They also exhibit deeper trap energy levels and increased trap density, thereby enhancing the sheet charge density of C₈-PTCDI (D) electrets (7.47 × 10¹² cm⁻²). As a result, devices based on n-type electrets demonstrate lower operation voltage (2 V) of transistors, lower operation voltage (20 V) of memories, and lower energy consumption (3.5 fJ per spike) of artificial synapses compared to those without n-type electrets.     

利用MoO3为电极修饰层的F16CuPc/ CuPc异质结的双极性有机场效应晶体管

在本文中,我们利用钛青铜(CuPc)和氟化钛青铜(F16CuPc)作为空穴传输层和电子传输层的制备了具有异质结结构的有机场效应晶体管(OFETs)。与单层的F16CuPc晶体管相比,异质结结构的晶体管的电子迁移率从3.1×10-3cm2/Vs提高至8.7×10-3cm2/vs,然而,空穴的传输行为却没有被观测到。为了提高空穴的注入能力,我们利用MoO3对源-漏电极进行了修饰,有效地改善了空穴注入。并进一步证实了MoO3的引入使得器件的接触电阻变小,平衡了电子和空穴的注入,从而最终实现了器件的双极性传输。     

Recent Advances in Ambipolar Transistors for Functional Applications

Ambipolar transistors represent a class of transistors where positive (holes) and negative (electrons) charge carriers both can transport concurrently within the semiconducting channel. The basic switching states of ambipolar transistors are comprised of common off‐state and separated on‐state mainly impelled by holes or electrons. During the past years, diverse materials are synthesized and utilized for implementing ambipolar charge transport and their further emerging applications comprising ambipolar memory, synaptic, logic, and light‐emitting transistors on account of their special bidirectional carrier‐transporting characteristic. Within this review, recent developments of ambipolar transistor field involving fundamental principles, interface modifications, selected semiconducting material systems, device structures, ambipolar characteristics, and promising applications are highlighted. The existed challenges and prospective for researching ambipolar transistors in electronics and optoelectronics are also discussed. It is expected that the review and outlook are well timed and instrumental for the rapid progress of academic sector of ambipolar transistors in lighting, display, memory, as well as neuromorphic computing for artificial intelligence.     

Phototuning Selectively Hole and Electron Transport in Optically Switchable Ambipolar Transistors

One of the grand challenges in organic electronics is to develop multicomponent materials wherein each component imparts a different and independently addressable property to the hybrid system. In this way, the combination of the pristine properties of each component is not only preserved but also combined with unprecedented properties emerging from the mutual interaction between the components. Here for the first time, that tri‐component materials comprised of an ambipolar diketopyrrolopyrrole‐based semiconducting polymer combined with two different photochromic diarylethene molecules possessing ad hoc energy levels can be used to develop organic field‐effect transistors, in which the transport of both, holes and electrons, can be photo‐modulated. A fully reversible light‐switching process is demonstrated, with a light‐controlled 100‐fold modulation of p‐type charge transport and a tenfold modulation of n‐type charge transport. These findings pave the way for photo‐tunable inverters and ultimately for completely re‐addressable high‐performance circuits comprising optical storage units and ambipolar field‐effect transistors.     

Low-Cost Nucleophilic Organic Bases as n-Dopants for Organic Field-Effect Transistors and Thermoelectric Devices

Doping is a powerful technique for tuning the electrical properties of organic semiconductors (OSCs). Although numerous studies are performed on OSC doping, thus far only a few n-type dopants have been developed. Herein, two low-cost nucleophilic organic bases are reported, namely 1,5,7-Triazabicyclo [4.4.0] dec-5-ene (TBD) and 1,5-Diazabicyclo [4.3.0] non-5-ene (DBN) for n-doping of OSCs. The two dopants are found to significantly enhance the electrical conductivity of OSCs. In particular, compared to the classic n-dopant 4-(2,3-Dihydro-1,3-dimethyl-1H-benzimidazol-2-yl)-N, N-dimethylbenzylamine (N-DMBI), DBN results in significantly higher conductivity and also lower activation energy in N2200 films, indicating its high doping performance. The utilization of the n-dopants for improving device performance and controlling the device polarity of organic field-effect transistors are demonstrated. Furthermore, these dopants are employed for fabricating organic thermoelectric devices, and the power factor value of DBN-doped N2200 films is found to be about 1.6 times higher than that of N-DMBI-doped films. These results show the feasibility of using low-cost organic bases as efficient n-dopants and demonstrate their promising applications in organic electronics.     

Solution‐Processed Small‐Molecule Bulk Heterojunction Ambipolar Transistors

Solution‐processed small‐molecule bulk heterojunction (BHJ) ambipolar organic thin‐film transistors are fabricated based on a combination of [2‐phenylbenzo[d,d']thieno[3,2‐b;4,5‐b']dithiophene (P‐BTDT) : 2‐(4‐n‐octylphenyl)benzo[d,d ']thieno[3,2‐b;4,5‐b']dithiophene (OP‐BTDT)] and C₆₀. Treating high electrical performance vacuum‐deposited P‐BTDT organic semiconductors with a newly developed solution‐processed organic semiconductor material, OP‐BTDT, in an optimized ratio yields a solution‐processed p‐channel organic semiconductor blend with carrier mobility as high as 0.65 cm² V^?1 s^?1. An optimized blending of P‐BTDT:OP‐BTDT with the n‐channel semiconductor, C₆₀, results in a BHJ ambipolar transistor with balanced carrier mobilities for holes and electrons of 0.03 and 0.02 cm² V^?1 s^?1, respectively. Furthermore, a complementary‐like inverter composed of two ambipolar thin‐film transistors is demonstrated, which achieves a gain of 115.     

Heterojunction Ambipolar Organic Transistors Fabricated by a Two‐Step Vacuum‐Deposition Process

Ambipolar organic field‐effect transistors (OFETs) are produced, based on organic heterojunctions fabricated by a two‐step vacuum‐deposition process. Copper phthalocyanine (CuPc) deposited at a high temperature (250 °C) acts as the first (p‐type component) layer, and hexadecafluorophthalocyaninatocopper (F₁₆CuPc) deposited at room temperature (25 °C) acts as the second (n‐type component) layer. A heterojunction with an interpenetrating network is obtained as the active layer for the OFETs. These heterojunction devices display significant ambipolar charge transport with symmetric electron and hole mobilities of the order of 10^–4 cm² V^–1 s^–1 in air. Conductive channels are at the interface between the F₁₆CuPc and CuPc domains in the interpenetrating networks. Electrons are transported in the F₁₆CuPc regions, and holes in the CuPc regions. The molecular arrangement in the heterojunction is well ordered, resulting in a balance of the two carrier densities responsible for the ambipolar electrical characteristics. The thin‐film morphology of the organic heterojunction with its interpenetrating network structure can be controlled well by the vacuum‐deposition process. The structure of interpenetrating networks is similar to that of the bulk heterojunction used in organic photovoltaic cells, therefore, it may be helpful in understanding the process of charge collection in organic photovoltaic cells.     

Bithienopyrroledione‐Based Copolymers,Versatile Semiconductors for Balanced Ambipolar Thin‐Film Transistors and Organic Solar Cells with V oc > 1 V

Conjugated polymer semiconductors P1 and P2 with bithienopyrroledione (bi‐TPD) as acceptor unit are synthesized. Their transistor and photovoltaic performances are investigated. Both polymers display high and balanced ambipolar transport behaviors in thin‐film transistors. P1‐ based devices show an electron mobility of 1.02 cm² V^?1 s^?1 and a hole mobility of 0.33 cm² V^?1 s^?1, one of the highest performance reported for ambipolar polymer transistors. The electron and hole mobilities of P2 transistors are 0.36 and 0.16 cm² V^?1 s^?1, respectively. The solar cells with PC₇₁BM as the electron acceptor and P1/P2 as the donor exhibit a high V _oc about 1.0 V, and a power conversion efficiency of 6.46% is observed for P1‐ based devices without any additives and/or post treatment. The high performance of P1 and P2 is attributed to their crystalline films and short π–π stacking distance (<3.5 Å). These results demonstrate (1) bi‐TPD is an excellent versatile electron‐deficient unit for polymer semiconductors and (2) bi‐TPD‐based polymer semiconductors have potential applications in organic transistors and organic solar cells.     

Sub-Femtojoule-Energy-Consumption Conformable Synaptic Transistors Based on Organic Single-Crystalline Nanoribbons

Inspired from powerful functionalities of human brain, artificial synapses are innovated continuously for the construction of brain-like neuromorphic electronics. The quest to rival the ultralow energy consumption of biological synapses has become highly compelling, but remains extremely difficult due to the lack of appropriate materials and device construction. In this study, organic single-crystalline nanoribbon active layer and elastic embedded photolithographic electrodes are first designed in synaptic transistors to reduce energy consumption of single device. The minimum energy consumption (0.29 fJ) of one synaptic event is far lower than that of biological synapse (10 fJ). Notably, sub-femtojoule-energy-consumption synaptic transistors can simulate various biological plastic behaviors even under different tensile and compressive strains, offering a new guidance for the construction of ultralow-energy-consuming neuromorphic electronic devices and the development of flexible artificial intelligence electronics in the future.     

Pressure‐Tunable Ambipolar Conduction and Hysteresis in Thin Palladium Diselenide Field Effect Transistors

Few‐layer palladium diselenide (PdSe₂) field effect transistors are studied under external stimuli such as electrical and optical fields, electron irradiation, and gas pressure. The ambipolar conduction and hysteresis are observed in the transfer curves of the as‐exfoliated and unprotected PdSe₂ material. The ambipolar conduction and its hysteretic behavior in the air and pure nitrogen environments are tuned. The prevailing p‐type transport observed at atmospheric pressure is reversibly turned into a dominant n‐type conduction by reducing the pressure, which can simultaneously suppress the hysteresis. The pressure control can be exploited to symmetrize and stabilize the transfer characteristics of the device as required in high‐performance logic circuits. The transistors are affected by trap states with characteristic times in the order of minutes. The channel conductance, dramatically reduced by the electron irradiation during scanning electron microscope imaging, is restored after an annealing of several minutes at room temperature. The work paves the way toward the exploitation of PdSe₂ in electronic devices by providing an experiment‐based and deep understanding of charge transport in PdSe₂ transistors subjected to electrical stress and other external agents.     

Quinoidal Molecules as a New Class of Ambipolar Semiconductor Originating from Amphoteric Redox Behavior

The two small molecules, quinoidal bithiophene (QBT) and quinoidal biselenophene (QBS), are designed based on a quinoid structure, and synthesized via a facile synthetic route. These quinoidal molecules have a reduced band gap and an amphoteric redox behavior, which is caused by an extended delocalization. Due to such properties, organic field‐effect transistors based on QBT and QBS have shown balanced ambipolar characteristics. After thermal annealing, the performances of the devices are enhanced by an increase in crystallinity. The field‐effect hole and electron mobilities are measured to be 0.031 cm² V^?1 s^?1 and 0.005 cm² V^?1 s^?1 for QBT, and 0.055 cm² V^?1 s^?1 and 0.021 cm² V^?1 s^?1 for QBS, respectively. In addition, we investigate the effect of chalcogen atoms (S and Se) on the molecular properties. The optical, electrochemical properties and electronic structures are mainly dominated by the quinoidal structure, whereas molecular properties are scarcely affected by either type of chalcogen atom. The main effect of the chalcogen atoms is ascribed to the difference of crystallinity. Due to a strong intermolecular interaction of the selenophene, QBS exhibits a higher degree of crystallinity, which leads to an enhancement of both hole and electron mobilities. Consequently, these types of quinoidal molecules are found to be promising for use as ambipolar semiconductors.     

Ferroelectrics-Electret Synergetic Organic Artificial Synapses with Single-Polarity Driven Dynamic Reconfigurable Modulation

Most current studies of artificial synapses only mimic the static plasticity, which is far from achieving the complex behaviors of the human brain. The few reported dynamic reconfigurable synapses based on ambipolar transistors switch the operating states by voltages with opposite polarity, which impedes the development of highly efficient synaptic readout circuits. To improve the efficiency, flexibility, and biocompatibility of dynamic reconfigurable synapses, here a ferroelectrics-electret synergetic organic synaptic p-type transistor (FESOST) is devised. Owing to the synergetic action of ferroelectric polarization switching and charge capture, FESOST exhibits single-polarity driven dynamic reconfigurable operating states with different synaptic behaviors (potentiation and depression) in response to the same gate pulse in different modes (excitatory and inhibitory). In addition, various single-polarity driven synaptic behaviors including short-term/long-term plasticity, paired-pulse facilitation/depression, spike-rate-dependent plasticity, and spike-number-dependent plasticity are also simulated. Finally, the reconfigurable artificial temperature perception system is simulated for the complex emotions of humans in response to different weather stimuli for people of different constitutions. The novel device architecture represents a major step forward in the development of dynamic, reconfigurable, high-efficiency, organic synapses.     

Tuning Optoelectronic Properties of Ambipolar Organic Light‐ Emitting Transistors Using a Bulk‐Heterojunction Approach

Bulk‐heterojunction engineering is demonstrated as an approach to producing ambipolar organic light‐emitting field‐effect transistors with tunable electrical and optoelectronic characteristics. The electron and hole mobilities, as well as the electroluminescence intensity, can be tuned over a large range by changing the composition of a bimolecular mixture consisting of α‐quinquethiophene and N,N′‐ditridecylperylene‐3,4,9,10‐tetracarboxylic‐diimide. Time‐resolved photoluminescence spectroscopy reveals that the phase segregation of the two molecules in the bulk heterojunction and their electronic interaction determine the optoelectronic properties of the devices. The results presented show that the bulk‐heterojunction approach, which is widely used in organic photovoltaic cells, can be successfully employed to select and tailor the functionality of field‐effect devices, including ambipolar charge transport and light emission.     

Recent Developments and Novel Applications of Thin Film,Light‐Emitting Transistors

Light‐emitting field‐effect transistors (LEFETs) combine switching and amplification with light emission and thus represent an interesting optoelectronic device. They are not limited anymore to a few examples and specific materials but are nearly universal for a wide range of semiconductors, from organic to inorganic and nanoscale. This review introduces the basic working principles of lateral unipolar and ambipolar LEFETs and discusses recent examples based on various solution‐processed semiconducting materials. Applications beyond simple light emission are presented and possible future directions for light‐emitting transistors with added functionalities are outlined.     

Solution‐Processed Ambipolar Field‐Effect Transistor Based on Diketopyrrolopyrrole Functionalized with Benzothiadiazole

Ambipolar charge transport in a solution‐processed small molecule 4,7‐bis{2‐[2,5‐bis(2‐ethylhexyl)‐3‐(5‐hexyl‐2,2′:5′,2″‐terthiophene‐5″‐yl)‐pyrrolo[3,4‐c]pyrrolo‐1,4‐dione‐6‐yl]‐thiophene‐5‐yl}‐2,1,3‐benzothiadiazole (BTDPP2) transistor has been investigated and shows a balanced field‐effect mobility of electrons and holes of up to ～10^?2 cm² V^?1 s^?1. Using low‐work‐function top electrodes such as Ba, the electron injection barrier is largely reduced. The observed ambipolar transport can be enhanced over one order of magnitude compared to devices using Al or Au electrodes. The field‐effect mobility increases upon thermal annealing at 150 °C due to the formation of large crystalline domains, as shown by atomic force microscopy and X‐ray diffraction. Organic inverter circuits based on BTDPP2 ambipolar transistors display a gain of over 25.     

Electrospun Nanofiber-Based Synaptic Transistor with Tunable Plasticity for Neuromorphic Computing

Biological synapses are the operational connection of the neurons for signal transmission in neuromorphic networks and hardware implementation combined with electrospun 1D nanofibers have realized its functionality for complicated computing tasks in basic three-terminal field-effect transistors with gate-controlled channel conductance. However, it still lacks the fundamental understanding that how the technological parameters influence the signal intensity of the information processing in the neural systems for the nanofiber-based synaptic transistors. Here, by tuning the electrospinning parameters and introducing the channel surface doping, an electrospun ZnO nanofiber-based transistor with tunable plasticity is presented to emulate the changing synaptic functions. The underlying mechanism of influence of carrier concentration and mobility on the device's electrical and synaptic performance is revealed as well. Short-term plasticity behaviors including paired-pulse facilitation, spike duration-dependent plasticity, and dynamic filtering are tuned in this fiber-based device. Furthermore, Perovskite-doped devices with ultralow energy consumption down to ≈0.2554 fJ and their handwritten recognition application show the great potential of synaptic transistors based on a 1D nanostructure active layer for building next-generation neuromorphic networks.     

Biomimetic Artificial Tetrachromatic Photoreceptors Based on Fully Light-Controlled 2D Transistors

Artificial photoreceptors offer a promising solution for developing biomimetic vision systems that incorporate in-sensor processing, which can greatly reduce power consumption and operation latency compared to traditional machine vision systems. This work presents a tetrachromatic optical synaptic device based on a 2D tungsten diselenide optoelectronic p-type transistor with a unique UV light-activated surface electron doping layer. Fully light-controlled bidirectional synaptic excitation and inhibition are demonstrated with visible and UV light stimuli, respectively, with a reasonable power density of <10 mW cm⁻² that matches the imaging condition of a biological vision. The weight updates of up to 64 states, high dynamic range, and low nonlinearity are demonstrated for long-term potentiation and depression behaviors. This artificial tetrachromatic photoreceptor can mimic the alert and foraging behaviors of a reindeer with low power consumption and enhanced signal contrast. Furthermore, it can be employed as an intelligent collision detection solution with in-sensor processing capabilities. This bioinspired tetrachromatic photoreceptor offers a low-cost, energy-efficient, and low-latency solution for future artificial machines.     

Stable Delocalized Singlet Biradical Hydrocarbon for Organic Field‐Effect Transistors

Delocalized singlet biradical hydrocarbons hold promise as new semiconducting materials for high‐performance organic devices. However, to date biradical organic molecules have attracted little attention as a material for organic electronic devices. Here, this work shows that films of a crystallized diphenyl derivative of s‐indacenodiphenalene (Ph₂‐IDPL) exhibit high ambipolar mobilities in organic field‐effect transistors (OFETs). Furthermore, OFETs fabricated using Ph₂‐IDPL single crystals show high hole mobility (μ_h = 7.2 × 10^?1 cm² V^?1 s^?1) comparable to that of amorphous Si. Additionally, high on/off ratios are achieved for Ph₂‐IDPL by inserting self‐assembled mono­layer of alkanethiol between the semiconducting layer and the Au electrodes. These findings open a door to the application of ambipolar OFETs to organic electronics such as complementary metal oxide semiconductor logic circuits.