Balanced Ambipolar Research Articles

Conformational Isomerization Promotes Balanced Ambipolar Transport for Efficient Narrowband Near-Ultraviolet Fluorophore and Non-doped Device with Low Efficiency Roll-Off

Conformational Isomerization Promotes Balanced Ambipolar Transport for Efficient Narrowband Near-Ultraviolet Fluorophore and Non-doped Device with Low Efficiency Roll-Off

Thiazole-Flanked Thiazoloisoindigo as a Monomer for Balanced Ambipolar Polymeric Field-effect Transistors

Thiazole-Flanked Thiazoloisoindigo as a Monomer for Balanced Ambipolar Polymeric Field-effect Transistors

Semi-interpenetrating network of polymer semiconductor and tetrapod nanocrystal assemblies with balanced ambipolar transport

Most organic semiconductors exhibit p-type electrical characteristics, whereas inorganic semiconductor nanocrystals typically possess n-type characteristics. Therefore, in principle, blending these two different materials can yield ambipolar transport for both electron and hole conduction if a percolation pathway for each charge carrier can be developed within the blended material. As the dimensions of these materials are on the nanometer scale, forming such a percolation pathway is challenging. Herein, we report a solution-processed method to construct an ambipolar channel by combining tetrapod-shaped CdSe nanocrystals and polythiophene. A fully percolated network of tetrapod CdSe nanocrystals were first produced by benefitting from the extended geometry of the nanostructure with four arms. The voids of the network were then filled with polythiophene, leading to a semi-interpenetrating network containing percolation pathways for both electrons and holes. A balanced ambipolar transport was achieved with electron and hole conductivities of 10.6 S/cm and 16.2 S/cm, respectively. The hybridization strategy for organic/inorganic semiconductors presented herein provides an innovative route to prepare solution-processable thin films for both electron and hole transport electronic devices.

Ambipolar carbon nanotube transistors with hybrid nanodielectric for low-voltage CMOS-like electronics

The proliferation of place-and-forget devices driven by the exponentially-growing Internet of Things industry has created a demand for low-voltage thin-film transistor (TFT) electronics based on solution-processible semiconductors. Amongst solution-processible technologies, TFTs based on semiconducting single-walled carbon nanotubes (sc-SWCNTs) are a promising candidate owing to their comparatively high current driving capability in their above-threshold region at low voltages, which is desirable for applications with constraints on supply voltage and switching speed. Low-voltage above-threshold operation in sc-SWCNTs is customarily achieved by using high-capacitance-density gate dielectrics such as metal-oxides fabricated via atomic layer deposition (ALD) and ion-gels. These are unattractive, as ALD requires complex-processing or exotic precursors, while ion-gels lead to slower devices with poor stability. This work demonstrates the fabrication of low-voltage above-threshold sc-SWCNTs TFTs based on a high-capacitance-density hybrid nanodielectric, which is composed of a readily-made AlO x nanolayer and a solution-processed self-assembled monolayer (SAM). The resultant TFTs can withstand a gate-channel voltage of 1–2 V, which ensures their above-threshold operation with balanced ambipolar behavior and electron/hole mobilities of 7 cm2 V−1 s−1. Key to achieving balanced ambipolarity is the mitigation of environmental factors via the encapsulation of the devices with an optimized spin-on polymer coating, which preserves the inherent properties of the sc-SWCNTs. Such balanced ambipolarity enables the direct implementation of CMOS-like circuit configurations without the use of additional dopants, semiconductors or source/drain electrode metals. The resultant CMOS-like inverters operate in the above-threshold region with supply voltages in the 1–2 V range, and have positive noise margins, gain values surpassing 80 V/V, and a bandwidth exceeding 100 kHz. This reinforces SAM-based nanodielectrics as an attractive route to easy-to-fabricate sc-SWCNT TFTs that can operate in the above-threshold region and that can meet the demand for low-voltage TFT electronics requiring moderate speeds and higher driving currents for wearables and sensing applications.

2D MXene-Molecular Hybrid Additive for High-Performance Ambipolar Polymer Field-Effect Transistors and Logic Gates.

MXenes are highly conductive layered materials that are attracting a great interest for high-performance opto-electronics, photonics, and energy applications.. Their non-covalent functionalization with ad hoc molecules enables the production of stable inks of 2D flakes to be processed in thin-films. Here, the formation of stable dispersions via the intercalation of Ti3 C2 Tx with didecyldimethyl ammonium bromide (DDAB) yielding Ti3 C2 Tx -DDAB, is demonstrated. Such functionalization modulates the properties of Ti3 C2 Tx , as evidenced by a 0.47eV decrease of the work function. It is also shown that DDAB is a powerful n-dopant capable of enhancing electron mobility in conjugated polymers and 2D materials. When Ti3 C2 Tx -DDAB is blended with poly(diketopyrrolopyrrole-co-selenophene) [(PDPP-Se)], a simultaneous increase by 170% and 152% of the hole and electron field-effect mobilities, respectively, is observed, compared to the neat conjugated polymer, with values reaching 2.0 cm2 V-1 s-1 . By exploiting the balanced ambipolar transport of the Ti3 C2 Tx -DDAB/PDPP-Se hybrid, complementary metal-oxide-semiconductor (CMOS) logic gates are fabricated that display well-centered trip points and good noise margin (64.6% for inverter). The results demonstrate that intercalant engineering represents an efficient strategy to tune the electronic properties of Ti3 C2 Tx yielding functionalized MXenes for polymer transistors with unprecedented performances and functions.

Balanced Ambipolar Charge Transport in Phenacene/Perylene Heterojunction-Based Organic Field-Effect Transistors.

Electronic devices relying on the combination of different conjugated organic materials are considerably appealing for their potential use in many applications such as photovoltaics, light emission, and digital/analog circuitry. In this study, the electrical response of field-effect transistors achieved through the evaporation of picene and PDIF-CN2 molecules, two well-known organic semiconductors with remarkable charge transport properties, was investigated. With the main goal to get a balanced ambipolar response, various device configurations bearing double-layer, triple-layer, and codeposited active channels were analyzed. The most suitable choices for the layer deposition processes, the related characteristic parameters, and the electrode position were identified to this purpose. In this way, ambipolar organic field-effect transistors exhibiting balanced mobility values exceeding 0.1 cm2 V–1 s–1 for both electrons and holes were obtained. These experimental results highlight also how the combination between picene and PDIF-CN2 layers allows tuning the threshold voltages of the p-type response. Scanning Kelvin probe microscopy (SKPM) images acquired on picene/PDIF-CN2 heterojunctions suggest the presence of an interface dipole between the two organic layers. This feature is related to the partial accumulation of space charge at the interface being enhanced when the electrons are depleted in the underlayer.

Diketopyrrolopyrrole-Based Dual-Acceptor Copolymers to Realize Tunable Charge Carrier Polarity of Organic Field-Effect Transistors and High-Performance Nonvolatile Ambipolar Flash Memories

Incorporation of dual acceptors into the copolymer backbone can effectively improve the electron affinity to achieve ambipolarity for use in specific electronic devices, for example, organic field-effect transistors (OFETs) and flash memories. Herein, two diketopyrrolopyrrole (DPP)-based copolymers, pDPPy-BTz and pDPPy-ffBTA, are developed by introducing dialkoxybithiazole and difluorobenzotriazole, respectively. Upon evaluating their electrical properties in OFETs, the polarity of dominant carriers in the OFET channel is found to be tuned by the monomer structures and measurement atmosphere. Specifically, the device based on pDPPy-BTz exhibits a p-type dominant ambipolar character with a μh/μe of 5.3 in air, whereas the electron mobility is enhanced by removing the oxygen and water (vacuum condition), resulting in a charge carrier polarity change to display an n-type dominant feature with the μh/μe decreasing to 0.3. Owing to the electron-donating property of thiophene groups, the pDPPy-ffBTA polymer exhibits a p-type unipolar performance in air and balanced ambipolar (μh/μe = 0.8) charge carrier transport under vacuum. On account of the well-defined ambipolar behavior, the polymers are used in nonvolatile memory devices. High performance is obtained with both polymers with memory windows of 10–16 V, stable data retention of over 105 s, and high reliability during >500 programming and erasing cycles. Overall, this study demonstrates a charge carrier polarity change in OFETs fabricated with DPP-based dual-acceptor copolymers by incorporating various acceptors into the polymer backbone and reports a high-performance nonvolatile ambipolar flash memory.

Tuning Biradical Character to Enable High and Balanced Ambipolar Charge Transport in a Quinoidal π-System.

Herein, two bis(dicyanomethylene)-substituted quinoidal molecules QBDT and QTBDT-3H were designed and synthesized to explore the open-shell effect on tuning the charge transport behavior of organic π-functional materials. The biradical character of QTBDT-3H was confirmed by DFT calculation, variable-temperature NMR, electron spin resonance (ESR), and superconducting quantum-interfering device (SQUID). The open-shell character enables QTBDT-3H an ambipolar characteristic under ambient conditions with highly balanced electron and hole mobilities of 0.32 and 0.16 cm2 V-1 s-1, respectively.

Interfacial and bulk charge transport in indolo[2,3-a]carbazole

Charge transport has been studied in indolo[2,3-a]carbazole, IC, a pentacyclic polyheteroaromatic system that can be easily synthesised using a one-step methodology. The characterisation of thin film Organic Field Effect Transistors (OFETs) and by Time Of Flight (TOF) has been used to determine the mobility in the interfacial region of the transistor and in the bulk of an organic layer, respectively. The mobility dependence on low electric fields has been studied in devices that work under different conditions, showing dissimilar trends for OFETs and TOF measurements. Interestingly, the later revealed a balanced ambipolar transport with negative electric field dependence of hole and electron mobilities.

Tuning the Charge Carrier Polarity of Organic Transistors by Varying the Electron Affinity of the Flanked Units in Diketopyrrolopyrrole‐Based Copolymers

AbstractFine‐tuning of the charge carrier polarity in organic transistors is an important step toward high‐performance organic complementary circuits and related devices. Here, three new semiconducting polymers, namely, pDPF‐DTF2, pDPSe‐DTF2, and pDPPy‐DTF2, are designed and synthesized using furan, selenophene, and pyridine flanking group‐based diketopyrrolopyrrole cores, respectively. Upon evaluating their electrical properties in transistor devices, the best performance has been achieved for pDPSe‐DTF2 with the highest and average hole mobility of 1.51 and 1.22 cm2 V−1 s−1, respectively. Most intriguingly, a clear charge‐carrier‐polarity change is observed when the devices are measured under vacuum. The pDPF‐DTF2 polymer exhibits a balanced ambipolar performance with the µh/µe ratio of 1.9, whereas pDPSe‐DTF2 exhibits p‐type dominated charge carrier transport properties with the µh/µe ratio of 26.7. Such a charge carrier transport change is due to the strong electron‐donating nature of the selenophene. Furthermore, pDPPy‐DTF2 with electron‐withdrawing pyridine flanking units demonstrates unipolar n‐type charge transport properties with an electron mobility as high as 0.20 cm2 V−1 s−1. Overall, this study demonstrates a simple yet effective approach to switch the charge carrier polarity in transistors by varying the electron affinity of flanking groups of the diketopyrrolopyrrole unit.

Ambipolarity and Air Stability of Silicon Phthalocyanine Organic Thin‐Film Transistors

AbstractSilicon phthalocyanines (SiPcs) are a class of conjugated, planar molecule that have recently been investigated for use in organic photovoltaics (OPVs), organic light‐emitting diodes (OLEDs), and organic thin‐film transistors (OTFTs) due to their variable structure and ease of synthesis. Bottom‐gate, bottom‐contact OTFTs with four SiPc derivatives used as the semiconducting layers are prepared using physical vapor deposition. Devices using bis(pentafluorophenoxy) silicon phthalocyanine (F10‐SiPc) deposited on 140 °C substrates demonstrate electron field‐effect mobilities (μ) of up to 0.54 cm2 V−1 s−1, among the best currently reported for N‐type phthalocyanine‐based transistors. All materials show dramatic changes in charge transport when characterized under vacuum (P < 0.1 Pa) compared to in air at atmospheric pressure, typically switching from electron majority charge carriers to holes, with the change dependent on material structure and energetics. F10‐SiPc is close to balanced ambipolar in air, with μ around 5 × 10−3 cm2 V−1 s−1 for both holes and electrons. These results demonstrate SiPcs' potential as N‐type semiconductors in OTFTs as well as their adjustable charge transport as affected by operation environment.

Diketopyrrolopyrrole tailoring charge transport characteristics of naphthalene diimide based polymers: From unipolar n‐typed to ambipolar polymers

ABSTRACTRandom copolymerization approach is confirmed to be an effective way to tailor the electronic structure and crystallinity of donor–acceptor copolymers. Diketopyrrolopyrroles (DPPs) as the second acceptor units with variable ratios were incorporated into naphthalene diimide (NDI)‐based polymers to obtained three low‐band‐gap random copolymers (P1–3). The low incorporation (10 and 30%) of DPP units did not substantially raise HOMO levels; thus, both P1 and P2 still exhibited unipolar n‐channel characteristics. When the incorporation of DPP increased to 50%, the major carries in organic field effect transistor (OFET) in P3 were switched from n‐channel to balanced ambipolar without sacrificing the electron mobility. However, P4, an alternating polymer of NDI and DPP with defined structure, exhibited unipolar n‐type transport characteristics because of the suppressed HOMO level. Polymer crystallinity and general macromolecular order have been studied carefully and discussed as it pertains to OFET performance. The present work thus highlights the structure–property relationship and the electronic tunability required in NDI‐based polymers to produce ambipolar transistors. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 46926.

Triple Acceptors in a Polymeric Architecture for Balanced Ambipolar Transistors and High‐Gain Inverters

The exploration of novel molecular architectures is crucial for the design of high-performance ambipolar polymer semiconductors. Here, a "triple-acceptors architecture" strategy to design the ambipolar polymer DPP-2T-DPP-TBT is introduced. The utilization of this architecture enables DPP-2T-DPP-TBT to achieve deep-lying highest occupied molecular orbital (HOMO)/lowest unoccupied molecular orbital (LUMO) levels of -5.38/-4.19 eV, and strong intermolecular interactions, which are favorable for hole/electron injection and intermolecular hopping through π-stacking. All these factors result in excellent ambipolar transport characteristics and promising applications in complementary-like circuits for DPP-2T-DPP-TBT under ambient conditions with high hole/electron mobilities and a gain value of up to 3.01/3.84 cm2 V-1 s-1 and 171, respectively, which are among the best performances in ambipolar polymer organic thin-film transistors and associated complementary-like circuits, especially in top-gate device configuration with low-cost glass as substrates. These results demonstrate that the "triple-acceptors architecture" strategy is an effective way for designing high-performance ambipolar polymer semiconductors.

Cyano-substituted benzochalcogenadiazole-based polymer semiconductors for balanced ambipolar organic thin-film transistors

Two new cyano-substituted benzochalcogenadiazoles were copolymerized with bithiophene, and the polymers show well balanced ambipolarity in transistors.

Effect of fluorination of naphthalene diimide-benzothiadiazole copolymers on ambipolar behavior in field-effect transistors.

Two naphthalene diimide (NDI)–benzothiadiazole (BT) based conjugated polymers with high molecular weight, P1 and P2, were synthesized by introducing F atoms to modulate the electron-donating ability of the BT moiety. 3-Decyl-pentadecyl branched alkyl side chains were employed and expected to improve the molecular organization and device performance. Both polymers have excellent solubility in common organic solvents. UV-vis-NIR absorption and cyclic voltammetry indicate that the maximum absorption wavelength of P2 is blue-shifted and the HOMO energy level of P2 is decreased in comparison with P1. Two dimensional wide angle X-ray scattering of thin films revealed a similar organization of both polymers. A less balanced transport in field-effect transistors with increased electron mobility of 0.258 cm2 V−1 s−1 and lowered hole transport of 2.4 × 10−3 cm2 V−1 s−1 was found for P2. Polymer devices of P1 exhibited a balanced ambipolar transport, with a hole mobility of 0.073 cm2 V−1 s−1 and electron mobility of 0.086 cm2 V−1 s−1.

Bis-Diketopyrrolopyrrole Moiety as a Promising Building Block to Enable Balanced Ambipolar Polymers for Flexible Transistors.

A bis-diketopyrrolopyrrole (DPP dimer, 2DPP) core is synthesized with much stronger electron deficiency than DPP by homocoupling of DPP. 2DPP-based polymers, P2DPP-BT, P2DPP-TT, P2DPP-TVT, and P2DPP-BDT, are obtained. Top-gated organic field-effect transistors on plastic substrate are fabricated. Compared with their mono-DPP-based polymers, remarkable improvement of electron mobilities of P2DPPs is achieved. Meanwhile, their p-channel performance becomes higher.

A conjugated polymer with high planarity and extended π-electron delocalization via a quinoid structure prepared by short synthetic steps

A quinoidal polymer,PQuBTV, with high planarity and extended π-electron delocalization was synthesized by short synthetic steps. The polymerPQuBTVshowed balanced ambipolar and high charge carrier mobilities.

Polymer-sorted semiconducting carbon nanotube networks for high-performance ambipolar field-effect transistors.

Efficient selection of semiconducting single-walled carbon nanotubes (SWNTs) from as-grown nanotube samples is crucial for their application as printable and flexible semiconductors in field-effect transistors (FETs). In this study, we use atactic poly(9-dodecyl-9-methyl-fluorene) (a-PF-1-12), a polyfluorene derivative with asymmetric side-chains, for the selective dispersion of semiconducting SWNTs with large diameters (>1 nm) from plasma torch-grown SWNTs. Lowering the molecular weight of the dispersing polymer leads to a significant improvement of selectivity. Combining dense semiconducting SWNT networks deposited from an enriched SWNT dispersion with a polymer/metal-oxide hybrid dielectric enables transistors with balanced ambipolar, contact resistance-corrected mobilities of up to 50 cm2·V–1·s–1, low ohmic contact resistance, steep subthreshold swings (0.12–0.14 V/dec) and high on/off ratios (106) even for short channel lengths (<10 μm). These FETs operate at low voltages (<3 V) and show almost no current hysteresis. The resulting ambipolar complementary-like inverters exhibit gains up to 61.

Naphthalene Diimide Copolymers with Oligo(p-phenylenevinylene) and Benzobisoxazole for Balanced Ambipolar Charge Transport

A series of alternating and random donor (D)–acceptor (A) copolymers based on naphthalene diimide (NDI) as the acceptor and oligo(p-phenylenevinylene) (OPV) or benzobisoxazole (BBO) as the strong and weak donor, respectively, were designed and synthesized by Suzuki coupling and Horner–Wadsworth–Emmons polymerization. The effect of the varying donor strength of OPV and BBO on the photophysical, electrochemical, and semiconducting properties of the polymers was investigated. Absorption and emission spectra recorded for dilute chloroform solution and thin film showed increased intramolecular charge transfer for NDI-alt-OPV polymer compared to NDI-alt-BBO polymer. Cyclic voltammetry studies along with DFT (density functional theory) studies at the B3LYP/6-31g* level gave insight into the energy level (HOMO/LUMO) and molecular orientation of donor and acceptor along the polymer backbone. NDI-alt-OPV polymer exhibited rigid coplanar structure with extended π-conjugation which induced backbone planarity and crystallinity to the polymer. The inherent poor solubility of the NDI-alt-BBO prevented further device characterization of this polymer. Random copolymer having maximum 30% incorporation of BBO comonomer in NDI-r-OPV/BBO was found to be soluble for further characterization. Compared to NDI-alt-OPV, lowering of both energy levels LUMO (∼0.2 eV) and HOMO (∼0.5 eV) was observed for both NDI-alt-BBO and the NDI-r-OPV/BBO. Bottom gate–top contact organic field effect transistors (OFETs) of NDI-alt-OPV exhibited balanced ambipolar charge transport with average electron and hole mobility of 3.09 × 10–3 cm2 V–1 s–1 and 2.1 × 10–3 cm2 V–1 s–1, respectively, whereas the random copolymer incorporating both OPV and BBO units NDI-r-OPV/BBO showed dominant n-type charge transport with moderate 4 × 10–4 cm2 V–1 s–1 average electron mobility. The present work thus highlights the structure–property relationship and the electronic tunability required in this class of NDI-based polymers to produce ambipolar transistors.

Photo-Induced Balanced Ambipolar Charge Transport in Organic Field-Effect Transistors

Photo-induced balanced ambipolar transports in lead phthalocyanine organic field-effect transistor are observed. The transport mode of the device is changed from typical p-channel to ambipolar under illumination at 655 nm, 100 mW/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> . The physical origins of this phenomenon are resulted from the photo-induced energy barrier lowering for electrons injection at the source-channel interface, which is suggested to be the downward bending of orbital level in the channel material near the source by accumulation of photo generated holes there.