Yttrium Doped Copper (II) Oxide Hole Transport Material as Efficient Thin Film Transistor

This work reports development of yttrium doped copper oxide (Y−CuO) as a new hole transport material with supplemented optoelectronic character. The pure and Y-doped CuO thin films are developed through a solid-state method at 200 °C and recognized as high performance p-channel inorganic thin-film transistors (TFTs). CuO is formed by oxidative decomposition of copper acetylacetonate, yielding 100 nm thick and conductive (40.9 S cm⁻¹) compact films with a band gap of 2.47 eV and charge carrier density of ∼1.44×10¹⁹ cm⁻³. Yttrium doping generates denser films, Cu₂Y₂O₅ phase in the lattice, with a wide band gap of 2.63 eV. The electrical conductivity increases nine-fold on 2 % Y addition to CuO, and the carrier density increases to 2.97×10²¹ cm⁻³, the highest reported so far. The TFT devices perform remarkably with high field-effect mobility (μ_sat) of 3.45 cm² V⁻¹ s⁻¹ and 5.3 cm² V⁻¹ s⁻¹, and considerably high current-on/off ratios of 0.11×10⁴ and 9.21×10⁴, for CuO and Y−CuO films, respectively (at −1 V operating voltage). A very small width hysteresis, 0.01 V for CuO and 1.92 V for 1 % Y−CuO, depict good bias stability. Both the devices work in enhancement mode with stable output characteristics for multiple forward sweeps (5 to −60 V) at −1V_g.     

Conjoint use of Naphthalene Diimide and Fullerene Derivatives to Generate Organic Semiconductors for n–type Organic Thin Film Transistors

In this paper, we described the design, synthesis, and characterization of two novel naphthalene diimide (NDI) core-based targets modified with terminal fullerene (C₆₀) yield – so called S4 and S5 , in which NDI bearing 1 and 2 molecules of C₆₀, respectively. The absorption, electrochemical and thin-film transistor characteristics of the newly developed targets were investigated in detail. Both S4 and S5 displayed broad absorption in the 450–500 nm region, owing to the effect of conjugation due to fullerene functionalities. The electrochemical measurement suggested that the HOMO and the LUMO energy levels can be altered with the number of C₆₀ units. Both S4 and S5 were employed as organic semiconductor materials in n-channel transistors. The thin film transistor based on S4 exhibited superior electron mobility (μe) values ranging from 1.20×10⁻⁴ to 3.58×10⁻⁴ cm² V⁻¹ s⁻¹ with a current on-off ratio varying from 10² to 10³ in comparison with the performance of S5 based transistor, which exhibited μe ranging from 8.33×10⁻⁵ to 2.03×10⁻⁴ cm² V⁻¹ s⁻¹ depending on channel lengths.     

A High‐Performance Organic Field‐Effect Transistor Based on Platinum(II) Porphyrin: Peripheral Substituents on Porphyrin Ligand Significantly Affect Film Structure and Charge Mobility

Organic field‐effect transistors incorporating planar π‐conjugated metal‐free macrocycles and their metal derivatives are fabricated by vacuum deposition. The crystal structures of [H₂(OX)] (H₂OX=etioporphyrin‐I), [Cu(OX)], [Pt(OX)], and [Pt(TBP)] (H₂TBP=tetra‐(n‐butyl)porphyrin) as determined by single crystal X‐ray diffraction (XRD), reveal the absence of occluded solvent molecules. The field‐effect transistors (FETs) made from thin films of all these metal‐free macrocycles and their metal derivatives show a p‐type semiconductor behavior with a charge mobility (μ) ranging from 10^?6 to 10^?1 cm² V^?1 s^?1. Annealing the as‐deposited Pt(OX) film leads to the formation of a polycrystalline film that exhibits excellent overall charge transport properties with a charge mobility of up to 3.2×10^?1 cm² V^?1 s^?1, which is the best value reported for a metalloporphyrin. Compared with their metal derivatives, the field‐effect transistors made from thin films of metal‐free macrocycles (except tetra‐(n‐propyl)porphycene) have significantly lower μ values (3.0×10^?6–3.7×10^?5 cm² V^?1 s^?1).     

Annulated Azuleno[2,1,8-ija]azulenes: Synthesis and Properties

Non-alternant non-benzenoid hydrocarbons exhibit very different optical and electronic properties than their well-studied benzenoid analogues. However, preparing such structures with extended conjugation length, remains challenging. Herein, we report the synthesis and properties of azuleno[2,1,8-ija]azulene derivatives using a two-step sequence involving a four-fold aldol condensation between aromatic dialdehydes and readily available tetrahydropentalene-2,5-(1H,3H)-dione. Molecules with band gap values ranging from 1.69 to 2.14 eV and molar extinction coefficients (ϵ) of nearly 3×10⁵ M⁻¹ cm⁻¹ have been prepared. These annulene-like structures exhibit significant diatropic ring currents (aromatic), as supported by ¹H NMR spectroscopy and DFT calculations. Field-effect transistors (OFETs) using azuleno[2,1,8-ija]azulene derivatives as semiconductors exhibit charge mobility values of up to 0.05 cm² V⁻¹ s⁻¹.     

Semi‐perfluoroalkylated perylene diimides for conjugated polymers with high molecular weight and high electron mobility

Perylene diimides (PDIs) and their derivatives are excellent semiconductors, while conjugated polymers based on PDIs have limited applications because of their low electron mobility (μ_e) derived from low molecular weight. The reported maximum number‐average molecular weight (M_n) of related polymers is only 21 kDa because PDIs have very poor solubility due to strong π–π stacking of their big planar conjugated cores. Herein, it is found that suitable semi‐perfluoroalkyl groups could enhance the solubility of PDIs significantly, and a series of semi‐perfluoroalkyl modified conjugated polymers with high molecular weight and electron mobility were synthesized. The maximum M_n reaches 94.8 kDa [P(4C_F8C_H‐PDI‐T2)_HW]. In their space‐charge‐limited current (SCLC) devices, all polymers exhibit typical characters of electron transporting semiconductors, and the highest μ_e is up to 8.40 × 10⁻³ cm² V⁻¹ s⁻¹ [P(4C_F8C_H‐PDI‐T2)_HW], which is similar as that of widely used electron transporting semiconductor PC₆₁BM (6.41 × 10⁻³ cm² V⁻¹ s⁻¹). © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018 , 56, 116–124     

Robust Spirobifluorene Core Based Hole Transporters with High Mobility for Long-Life Green Phosphorescent Organic Light-Emitting Devices

Using a tailored high triplet energy hole transport layer (HTL) is a suitable way to improve the efficiency and extend the lifetime of organic light-emitting devices (OLEDs), which can use all molecular excitons of singlets and triplets. In this study, dibenzofuran (DBF)-end-capped and spirobifluorene (SBF) core-based HTLs referred as TDBFSBF1 and TDBFSBF2 were effectively developed. TDBFSBF1 exhibited a high glass transition temperature of 178 °C and triplet energy of 2.5 eV. Moreover, a high external quantum efficiency of 22.0 %, long operational lifetime at 50 % of the initial luminance of 89,000 h, and low driving voltage at 1000 cd m⁻² of 2.95 V were achieved in green phosphorescent OLEDs using TDBFSBF1 . Further, a high-hole mobility μ_h value of 1.9×10⁻³ cm² V⁻¹ s⁻¹ was recorded in TDBFSBF2 . A multiscale simulation successfully reproduced the experimental μ_h values and indicated that the reorganization energy was the primary factor in determining the mobility differences among these SBF core based HTLs.     

Tune the photoresponse of monolayer MoS2 by decorating CsPbBr3 perovskite nanoparticles

Tuning the photoresponse of monolayer MoS₂ could extend its potential application in many fields, however, it is still a challenge. In this study, CsPbBr₃ nanoparticles were prepared and spin-coated on the surface of monolayer MoS₂ to fabricate hybrid CsPbBr₃/MoS₂ photodetectors. By combing the photoelectrical property of the CsPbBr₃, the synergistic effect has been systematically studied from its carrier mobility, photoresponse and detectivity. It was found that nanofilm-coating of CsPbBr₃ would impede the photoelectric performance due to the electron-hole recombination facilitated by the defects at the interface of CsPbBr₃ and MoS₂ films. While the nanoparticles decorating was observed to significantly improve the conductivity of the monolayer MoS₂, which also increased the on/off ratio of the MoS₂ transistor from 8.2 × 10³ to 4.4 × 10⁴, and enhanced the carrier mobility from 0.090 cm² V⁻¹ s⁻¹ to 0.202 cm² V⁻¹ s⁻¹, ascribing to a mixed electron recombination-injection process. Furthermore, the CsPbBr₃ nanofilm would decrease the responsivity to 136 and 178 A/W under the light wavelength of 400 and 500 nm, respectively, while decorating CsPbBr₃ nanoparticles improve the photoresponse to 948 and 883 A/W with the detectivity at the level of 10¹¹ Jones. This work may provide an easy and cost-efficient way to tune the photoresponse of MoS₂ photodetectors.     

A Planarized Triphenylborane Mesogen: Discotic Liquid Crystals with Ambipolar Charge‐Carrier Transport Properties

A discotic liquid‐crystalline (LC) material, consisting of a planarized triphenylborane mesogen, was synthesized. X‐ray diffraction analysis confirmed that this compound forms a hexagonal columnar LC phase with an interfacial distance of 3.57 Å between the discs. At ambient temperature, this boron‐centered discotic liquid crystal exhibited ambipolar carrier transport properties with electron and hole mobility values of approximately 10^?3 and 3×10^?5 cm² V^?1 s^?1, respectively.     

Solution processable diketopyrrolopyrrole semiconductor: towards bio-electronic applications

In this paper, the possibility to use diketopyrrolopyrrole (DPP) for the construction of electrical devices designed to interact with animal cells was studied. For this purpose, the biocompatibility and electrical properties of the selected DPP derivative (3,6-bis(5-(benzofuran-2-yl)thiophen-2-yl)-2,5-bis(2-ethyl-hexyl)pyrrolo[3,4-c]pyrrole-1,4-dione) [referred as DPP(TBFu)₂] were researched. The electrical properties were studied using model organic field-effect transistors. Mainly investigated was under what conditions maximum charge carrier mobility can be achieved. Using the cumulative effect of self-assembled monolayers on dielectrics and electrodes and detailed thermal analysis of the DPP, a higher charge carrier mobility was achieved than has been previously reported (5.5?×?10^?3 cm² V^?1 s^?1). The biocompatibility was studied based on a culture of 3T3 fibroblasts. This research revealed that DPP(TBFu)₂ can be used in applications involving direct contact with living animal cells. The conclusions found with these model devices can be applied to components suitable for biosensing applications, e.g., water- or electrolyte-gated organic field-effect transistors.     

Intrinsically Low Thermal Conductivity and High Carrier Mobility in Dual Topological Quantum Material,n-Type BiTe

A challenge in thermoelectrics is to achieve intrinsically low thermal conductivity in crystalline solids while maintaining a high carrier mobility (μ). Topological quantum materials, such as the topological insulator (TI) or topological crystalline insulator (TCI) can exhibit high μ. Weak topological insulators (WTI) are of interest because of their layered hetero-structural nature which has a low lattice thermal conductivity (κ_lat). BiTe, a unique member of the (Bi₂)_m(Bi₂Te₃)_n homologous series (m:n=1:2), has both the quantum states, TCI and WTI, which is distinct from the conventional strong TI, Bi₂Te₃ (where m:n=0:1). Herein, we report intrinsically low κ_lat of 0.47–0.8 W m⁻¹ K⁻¹ in the 300–650 K range in BiTe resulting from low energy optical phonon branches which originate primarily from the localized vibrations of Bi bilayer. It has high μ≈516 cm² V⁻¹ s⁻¹ and 707 cm² V⁻¹ s⁻¹ along parallel and perpendicular to the spark plasma sintering (SPS) directions, respectively, at room temperature.     

Coordination Polymer Framework Based On‐Chip Micro‐Supercapacitors with AC Line‐Filtering Performance

On‐chip micro‐supercapacitors (MSCs) are important Si‐compatible power‐source backups for miniaturized electronics. Despite their tremendous advantages, current on‐chip MSCs require harsh processing conditions and typically perform like resistors when filtering ripples from alternating current (AC). Herein, we demonstrated a facile layer‐by‐layer method towards on‐chip MSCs based on an azulene‐bridged coordination polymer framework (PiCBA). Owing to the good carrier mobility (5×10⁻³ cm² V⁻¹ s⁻¹) of PiCBA, the permanent dipole moment of azulene skeleton, and ultralow band gap of PiCBA, the fabricated MSCs delivered high specific capacitances of up to 34.1 F cm⁻³ at 50 mV s⁻¹ and a high volumetric power density of 1323 W cm⁻³. Most importantly, such MCSs exhibited AC line‐filtering performance (−73° at 120 Hz) with a short resistance–capacitance constant of circa 0.83 ms.     

Simultaneous morphological stability and high charge carrier mobilities in donor–acceptor block copolymer/PCBM blends

Donor–acceptor block copolymers (BCP), incorporating poly(3‐hexylthiophene) (P3HT), and a polystyrene copolymer with pendant fullerenes (PPCBM) provide desired stable nanostructures, but mostly do not exhibit balanced charge carrier mobilities. This work presents an elegant approach to match hole and electron transport in BCP by blending with molecular PCBM without causing any macrophase separation. An insufficient electron mobility of PPCBM can be widely compensated by adding PCBM which is monitored by the space‐charge limited current method. Using X‐ray diffraction, atomic force microscopy, and differential scanning calorimetry, we verify the large miscibility of the PPCBM:PCBM blend up to 60 wt % PCBM load forming an amorphous, molecularly mixed fullerene phase without crystallization. Thus, blending BCP with PCBM substantially enhances charge transport achieving an electron mobility of μ_e=(3.2 ± 1.7) × 10^?4 cm²V^?1s^?1 and hole mobility of μ_h=(1.8 ± 0.6) × 10^?3 cm²V^?1s^?1 in organic field‐effect transistors (OFET). The BCP:PCBM blend provides a similarly high ambipolar charge transport compared to the established P3HT:PCBM system, but with the advantage of an exceptionally stable morphology even for prolonged thermal annealing. This work demonstrates the feasibility of high charge transport and stable morphology simultaneously in a donor–acceptor BCP by a blend approach. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 1125–1136     

Heptacene: Synthesis and Its Hole-Transfer Property in Stable Thin Films

Heptacene ( 1 ) has been produced via a monoketone precursor, 2 , which was prepared from 1,2,4,5-tetrabromobenzene in nine steps in a total yield of 10 %. Compound 2 was converted to 1 quantitatively by heating at 202 °C. Heptacene exhibited high thermal stability in the solid state without any observable change over two months. To investigate the potential value of 1 as a material for p-type organic field-effect transistors (OFETs), top-contact OFET devices were fabricated by vacuum deposition of 1 onto a hexamethyldisilazane (HMDS)/SiO₂/Si substrate. The best hole mobility performance was 2.2 cm² V⁻¹ s⁻¹. This is the first report of stable heptacene being used in an effective device and examined for its charge carrier properties.     

Conjugated polymers based on 1,8‐naphthalene monoimide with high electron mobility

1,4,8,9‐Naphthalene diimides (NDIs) with strong electron accepting ability and high stability are excellent building blocks for semiconductor polymers. However, 1,8‐naphthalene monoimide (NMI) with similar structure and energy levels as that of NDI has never been used to construct conjugated polymers because of synthetic difficulty. Herein, 3,6‐dibromo‐NMI (DBNMI) with bulky alkyl groups was obtained effectively in a four‐step synthesis, and three donor‐acceptor (D‐A) type conjugated polymers based on NMI were firstly prepared. These polymers have strong absorption in the range of 300–600 nm, low LUMO level of 3.68 eV, and moderate bandgaps of 2.18 eV. Space charge limiting current measurements indicate these polymers are typical electron transporting materials, and the highest electron mobility is up to 5.8 × 10⁻³ cm² V⁻¹ s⁻¹, which is close to the star acceptor based on NDI (N2200, 5.0 × 10⁻³ cm² V⁻¹ s⁻¹). © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018 , 56, 276–281     

New n-type semiconductor material based on styryl fullerene for organic field-effect transistors

Organic field-effect transistors with styryl fullerene as a semi conductor layer applied by centrifugation are considered. Electron mobility in the transistors was 0.067 ± 10% cm² V⁻¹ s⁻¹, whereas the mobility of electrons in these devices after the vacuum deposition of a semiconductor layer was much lower (0.023 ± 10% cm² V⁻¹ s⁻¹).     

Raman spectra of carriers in ionic-liquid-gated transistors fabricated with poly(2,5-bis(3-tetradecylthiophen-2-yl)thieno[3,2-b]thiophene)

We observed the Raman spectra of carriers, positive polarons and bipolarons, generated in a poly(2,5-bis(3-tetradecylthiophen-2-yl)thieno[3,2-b]thiophene) (PBTTT-C14) film by FeCl₃ vapor doping. Electrical conductivity and Raman measurements indicate that the dominant carriers in the conducting state were bipolarons. We identified positive polarons and bipolarons generated in an ionic-liquid-gated transistor (ILGT) fabricated with PBTTT-C14 as an active semiconductor and an ionic liquid 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl) imide [BMIM][TFSI] as a gate dielectric using Raman spectroscopy. The relationship between the source−drain current (I_D) at a constant source−drain voltage (V_D) and the gate voltage (V_G) was measured. I_D increased above −V_G = 1.1 V and showed a maximum at −V_G = 2.0 V. Positive polarons were formed at the initial stage of electrochemical doping (−V_G = 0.8 V). As I_D increased, positive bipolarons were formed. Above V_G = −2.0 V, bipolarons were dominant. The charge density (n), the doping level (x), and the mobility of the bipolarons were calculated from the electrochemical measurements. The highest mobility (μ) of bipolarons was 0.72 cm² V⁻¹ s⁻¹ at x = 110 mol%/repeating unit (−V_G = 2.0 V), whereas the highest μ of polarons was 4.6 × 10⁻⁴ cm² V⁻¹ s⁻¹ at x = 10 mol%.     

Electron-Deficient Polycyclic Molecules via Ring Fusion for n-Type Organic Electrochemical Transistors

The primary challenge for n-type small-molecule organic electrochemical transistors (OECTs) is to improve their electron mobilities and thus the key figure of merit μC*. Nevertheless, few reports in OECTs have specially proposed to address this issue. Herein, we report a 10-ring-fused polycyclic π-system consisting of the core of naphthalene bis-isatin dimer and the terminal moieties of rhodanine, which features intramolecular noncovalent interactions, high π-delocalization and strong electron-deficient characteristics. We find that this extended π-conjugated system using the ring fusion strategy displays improved electron mobilities up to 0.043 cm² V⁻¹ s⁻¹ compared to our previously reported small molecule gNR, and thereby leads to a remarkable μC* of 10.3 F cm⁻¹ V⁻¹ s⁻¹ in n-type OECTs, which is the highest value reported to date for small-molecule OECTs. This work highlights the importance of π-conjugation extension in polycyclic-fused molecules for enhancing the performance of n-type small-molecule OECTs.     

Study of the reactions of OH with HCl,HBr, and HI between 298 K and 460 K

The reactions between OH radicals and hydrogen halides (HCl, HBr, HI) have been studied between 298 and 460 K by using a discharge flow-electron paramagnetic resonance technique. The rate constants were found to be k_HCl(298 K) = (7.9 ± 1.3) × 10⁻¹³ cm³ molecule⁻¹ s⁻¹ with a weak positive temperature dependence, k_HBr (298-460 K) = (1.04 ± 0.2) × 10⁻¹¹ cm³ molecule⁻¹ s⁻¹, and k_HI(298 K) = (3.0 ± 0.3) × 10⁻¹¹ cm³ molecule⁻¹ s⁻¹, respectively. The homogeneous nature of these reactions has been experimentally tested.     

Near IR Bandgap Semiconducting 2D Conjugated Metal-Organic Framework with Rhombic Lattice and High Mobility

Two-dimensional conjugated metal–organic frameworks (2D c-MOFs) are emerging as a unique class of electronic materials. However, 2D c-MOFs with band gaps in the Vis-NIR and high charge carrier mobility are rare. Most of the reported conducting 2D c-MOFs are metallic (i.e. gapless), which largely limits their use in logic devices. Herein, we design a phenanthrotriphenylene-based, D_2h-symmetric π-extended ligand ( OHPTP ), and synthesize the first rhombic 2D c-MOF single crystals ( Cu₂(OHPTP) ). The continuous rotation electron diffraction (cRED) analysis unveils the orthorhombic crystal structure at the atomic level with a unique slipped AA stacking. The Cu₂(OHPTP) is a p-type semiconductor with an indirect band gap of ≈0.50 eV and exhibits high electrical conductivity of 0.10 S cm⁻¹ and high charge carrier mobility of ≈10.0 cm² V⁻¹ s⁻¹. Theoretical calculations underline the predominant role of the out-of-plane charge transport in this semiquinone-based 2D c-MOF.