Synergistic Effect of Oxoammonium Salt and Its Counterions for Fabricating Organic Electrochemical Transistors with Low Power Consumption

The state-of-the-art poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS)-based organic electrochemical transistors (OECTs) are gaining importance for a variety of biological applications due to their mixed electronic and ionic conductivities featuring ion-to-electron conversion. A low operation voltage without sacrificing device performance is desired to realize long-term monitoring of biological activities. In the present work, oxoammonium salts with two different counterions (TEMPO+X–, where TEMPO = 2,2,6,6-tetramethylpiperidine-1-oxoammonium; X = Br– and TFSI–) are employed as secondary dopants to modulate the device performance. Both oxoammonium salts feature a distinct dopant concentration-dependent doping effect, allowing precise control in improving the performance of OECTs. A zero-gate bias, corresponding to the maximum transconductance, and a low threshold voltage are realized by optimizing the dopant concentrations. In addition, TEMPO+TFSI– dopant exerts great capability in modulating the work function and in morphology reconstruction of PEDOT:PSS, ensuring a well-matched work function at the gold electrode–channel material interface and condensed microstructure stacking with an edge-on orientation in the doped PEDOT:PSS films. The synergistic effect of TEMPO and the TFSI– counterion endows the device with superior performance to its counterparts due to the resultant higher μC* figure, benefiting from the efficient injection/extraction of holes at the interface and enhanced intra- and inter-chain carrier transport. The excellent device performance makes the OECT a promising neuromorphic device to mimic basic brain functions

High-Performance Organic Field-Effect Transistors Fabricated Based on a Novel Ternary π‑Conjugated Copolymer

In this study, we developed a ternary conjugated polymer, IFBT-TT, consisting of centrosymmetric indaceno­[1,2-<i>b</i>:5,6-<i>b</i>′]­dithiophene and thieno­[3,2-<i>b</i>]­thiophene as the electron-donating units and an asymmetric 5-fluorobenzo­[<i>c</i>]­[1,2,5]­thiadiazole as the electron-accepting unit. The target copolymer was synthesized using an acceptor–donor–acceptor (A–D–A) type of macromonomer, which gave the target copolymer a precisely defined D1–A–D2–A architecture. Theoretical simulation revealed that the IFBT-TT features C–H···N and F···S nonbonding interactions, leading to a highly rigid and planar molecular backbone. Although the spin-cast IFBT-TT films exhibited an amorphous morphology lacking in ordered structures, the fabricated field-effect transistors presented remarkable p-type transport properties with high mobility of up to 5.0 cm² V^–1 s^–1 and excellent ambient stability. These observations highlight that the integration of a three-component D1–A–D2–A-type backbone framework is an effective molecular design strategy for high-mobility conjugated polymers

All Inkjet-Printed Metal-Oxide Thin-Film Transistor Array with Good Stability and Uniformity Using Surface-Energy Patterns

An array of inkjet-printed metal-oxide thin-film transistors (TFTs) is demonstrated for the first time with the assistance of surface-energy patterns prepared by printing pure solvent to etch the ultrathin hydrophobic layer. The surface-energy patterns not only restrained the spreading of inks but also provided a facile way to regulate the morphology of metal oxide films without optimizing ink formulation. The fully printed InGaO TFT devices in the array exhibited excellent electron transport characteristics with a maximum mobility of 11.7 cm² V^–1 s^–1, negligible hysteresis, good uniformity, and good stability under bias stress. The new route lights a general way toward fully inkjet-printed metal-oxide TFT arrays

High Efficiency and High <i>V</i>_oc Inverted Polymer Solar Cells Based on a Low-Lying HOMO Polycarbazole Donor and a Hydrophilic Polycarbazole Interlayer on ITO Cathode

In this work, poly­[<i>N</i>-9′-heptadecanyl-2,7-carbazole-<i>alt</i>-5,5-(4,7-di-2-thienyl-5,6-bis­(dodecyloxy)-2,1,3-benzothiadiazole)] (PCDTBT12) was synthesized as the polymer donor for photovoltaic application. PCDTBT12 possesses a band gap of 1.99 eV, a low-lying HOMO of −5.6 eV, and good hole mobility up to 4.1 × 10^–3 cm² V^–1 s^–1. With ZnO as the interlayer on an ITO cathode, a PCDTBT12-based inverted solar cell showed a high open-circuit voltage of 0.98 V and a good power conversion efficiency (PCE) of 5.53%, suggesting that PCDTBT12 would be a promising donor material in the fabrication of a subcell for shorter wavelength absorption in a tandem solar cell. Using PC-P, a homopolymer of 2,7-carbazole with hydrophilic phosphonate side chains, as an interlayer polymer on the ITO cathode could further elevate the efficiency to 6.04% because of increased current (higher efficiency of 6.2% was achieved for a smaller cell area of 0.045 cm²). The efficiencies are the highest ones so far reported for an inverted solar cell with an organic cathode interlayer. It was proposed that the hydrophilic side chains of PC-P supplied a subgap state for electron transport. The two devices showed comparable air stability, and retained over 96% of their initial PCEs after storage in air for more than 1 month. Therefore, a hydrophilic conjugated polymer as the cathode interlayer, already shown in outstanding cathode modifications in conventional polymer solar cells, will play an important role in the future development of high efficiency and air-stable inverted solar cells

Role of Evaporated Silver Nanoparticles in Organic Field-Effect Transistor: Electrical Effects and Dependence on the Size

The electrical effects of metal nanoparticles are determined by the nature of a single nanoparticle (shape, size, surface) and their correlation with the nanoscale electronic structure. In this work, we report that electrical properties of evaporated silver nanoparticles can be controlled by different thicknesses and thermal annealing times. The particle size and size distribution were first fully characterized by the AFM and optical extinction spectra, and then their electrical properties such as current trapping and threshold voltage were studied by the organic field-effect transistor with a device structure of Si/SiO₂/​Ag-NPs/PMMA/​PTB7/Ag. The results show that the thickness decrease and thermal annealing are effective ways for a lower charge trapping, which corresponds to smaller particle size and homogeneous particle distribution without particle aggregates. These results would be helpful for the optoelectronic applications of metal nanoparticles

Organic Photodiodes with Thermally Reliable Dark Current and Excellent Detectivity Enabled by Low Donor Concentration

Reducing the dark current (Jd) under reverse bias while maintaining a high external quantum efficiency (EQE) is essential for the practical application of organic photodiodes (OPDs). However, the high Jd of OPDs is generally difficult to reduce because its origin in organic photodiodes is still not well understood and is strongly temperature dependent. To address the issues related to high Jd in typical OPDs, we investigate fullerene-based OPDs with various donor concentrations. It is surprising that OPDs with a low donor concentration in the active layer can achieve a very low Jd of 1.68 × 10–7 mA cm–2 at a reverse bias of −2 V, which is almost temperature-independent owing to the low polymer content. More importantly, the fullerene-based OPDs with a low donor concentration of 5 wt % can still achieve an external quantum efficiency (EQE) as high as 40%, resulting in a promisingly high detectivity of above 1013 Jones at 300–800 nm compared to the OPDs with a standard donor/acceptor ratio. The presented optimized OPD device can also be used for real-time heart rate detection, indicating its potential for practical photon-sensing applications

Coffee-Ring Defined Short Channels for Inkjet-Printed Metal Oxide Thin-Film Transistors

Short-channel electronic devices several micrometers in length are difficult to implement by direct inkjet printing due to the limitation of position accuracy of the common inkjet printer system and the spread of functional ink on substrates. In this report, metal oxide thin-film transistors (TFTs) with channel lengths of 3.5 ± 0.7 μm were successfully fabricated with a common inkjet printer without any photolithography steps. Hydrophobic CYTOP coffee stripes, made by inkjet-printing and plasma-treating processes, were utilized to define the channel area of TFTs with channel lengths as short as ∼3.5 μm by dewetting the inks of the source/drain (S/D) precursors. Furthermore, by introduction of an ultrathin layer of PVA to modify the S/D surfaces, the spreading of precursor ink of the InO_<i>x</i> semiconductor layer was well-controlled. The inkjet-printed short-channel TFTs exhibited a maximum mobility of 4.9 cm² V^–1 s^–1 and an on/off ratio of larger than 10⁹. This approach of fabricating short-channel TFTs by inkjet printing will promote the large-area fabrication of short-channel TFTs in a cost-effective manner

High-Performance, Solution-Processed Quantum Dot Light-Emitting Field-Effect Transistors with a Scandium-Incorporated Indium Oxide Semiconductor

Light-emitting field-effect transistors (LEFETs) have attained great attention due to their special characteristics of both the switching capacity and the electroluminescence capacity. However, high-performance LEFETs with high mobility, high brightness, and high efficiency have not been realized due to the difficulty in developing high electron and hole mobility materials with suitable band structures. In this paper, quantum dot hybrid LEFETs (QD-HLEFETs) combining high-luminous-efficiency quantum dots (QDs) and a solution-processed scandium-incorporated indium oxide (Sc:In₂O₃) semiconductor were demonstrated. The red QD-HLEFET showed high electrical and optical performance with an electron mobility of 0.8 cm² V^–1 s^–1, a maximum brightness of 13 400 cd/m², and a maximum external quantum efficiency of 8.7%. The high performance of the QD-HLEFET is attributed to the good energy band matching between Sc:In₂O₃ and QDs and the balanced hole and electron injection (less exciton nonradiative recombination). In addition, incorporation of Sc into In₂O₃ can suppress the oxygen vacancy and free carrier generation and brings about excellent current and optical modulation (the on/off current ratio is 10⁵ and the on/off brightness ratio is 10⁶)