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A near-infrared aza-BODIPY dye is developed for organic photodetectors. The device achieves a high D* value and a fast-response speed of 0.5 μs. Importantly, our work innovatively utilizes the high-performance NIR OPD in the laser microphone system.

Understanding spinterfaces between magnetic metals and organic semiconductors is essential to unlock the great potentials that organic materials host for spintronic applications. Although plenty of efforts have been devoted to studying organic spintronic devices, exploring the role of metal/molecule spinterfaces at two-dimensional limit remains challenging because of excessive disorders and traps at the interfaces. Here, we demonstrate atomically smooth metal/molecule interfaces through nondestructively transferring magnetic electrodes on epitaxial grown single-crystalline layered organic films. Using such high-quality interfaces, we investigate spin injection of spin-valve devices based on organic films of different layers, in which molecules are packed in different manners. We find that the measured magnetoresistance and the estimated spin polarization increase markedly for bilayer devices compared with their monolayer counterparts. These observations reveal the key role of molecular packing on spin polarization, which is supported by density functional theory calculations. Our findings provide promising routes toward designing spinterfaces for organic spintronic devices.

Ferroelectric transistors hold great potential in low consumption devices. Due to the high film quality and clean system, two dimensional organic semiconductors are widely employed to fabricate high performance organic electronic devices and explore the modulation mechanism of the molecular packing on device performance. Here, we combine the ferroelectric hafnium oxide HfZrO x and two-dimensional molecular crystal 2,9-didecyldinaphtho[2,3-b:2′,3′-f]thieno[3,2b]thiophene (C10-DNTT) with controllable layers to study the molecular layer modulation of ferroelectric organic thin-film transistors (OTFTs). The contact resistance, driving current and transconductance are directly affected by the additional access resistance across the upper molecular layers at the source/drain contact region. Simultaneously, the capacitance of Schottky junction related to the molecular layer thickness could effectively adjust the gate potential acting on the organic channel, further controlling the devices’ subthreshold swing and transconductance efficiency. This work would promote the development of low voltage and high performance OTFTs.

Monolayer transition metal dichalcogenides (mTMDs) possess a direct band gap and strong PL emission that is highly sensitive to doping level and interfaces, laying the foundation for investigating the contact between mTMD and metal

Benefited from the advantages of light sensitivity of organic materials and high carrier mobility of graphene, organic semiconductor/graphene hybrid phototransistors exhibit ultrahigh photoconductive gain and photoresponsivity, attributed to the carrier multiplication effect in the organic layer. However, with single absorbing layer, the built-in electrical field between organic layer and graphene is insufficient, and spectral response range is limited. In this work, perylene-3,4,9,10-tetracarboxylic dianhydride (PTCDA) and 2,7-dioctyl[1]benzothieno[3,2-b][1]benzothiophene (C8-BTBT) organic tandem structure with high crystal quality fabricated via van der Waals vapor phase growth is adopted as the light absorbing layer, where suppressed carrier trap states density along with the additional charge-transfer interface between the organic layers result in overall improvement of device performance. Prominent photo-responses are observed with photoresponsivity up to 5.76 × 105A/W and photoconductive gain up to 1.38 × 109. Further more, complementary light absorption spectrum of these two organic materials fulfills effective photodetecting at ultraviolet and visible range.

Due to the absence of dangling bonds, the integration of ultra-thin dielectric on 2D semiconductors has become a huge challenge, and its reliability research has been blank before. For the first time, we report the high $-\mathcal{K}$ dielectric reliability on Mos2. By PTCDA crystal as interface layer, we demonstrated excellent reliability of HfO 2 /PTCDA gate stack, including EBD over 8.9 MV/cm, $\mathrm{E}_{\text{BD}}\ ^{10\text{yrs}}$ over 6.5 MV/cm and ultra-low BD rate, all of which show better reliability than HfO 2 /Si.

The development of organic thin-film transistors (OTFTs) with low power consumption and high gain will advance many flexible electronics. Here, by combining solution-processed monolayer organic crystal, ferroelectric HfZrOx gating and van der Waals fabrication, we realize flexible OTFTs that simultaneously deliver high transconductance and sub-60 mV/dec switching, under one-volt operating voltage. The overall optimization of transconductance, subthreshold swing and output resistance leads to transistor intrinsic gain and amplifier voltage gain over 5.3 × 104 and 1.1 × 104, respectively, which outperform existing technologies using organics, oxides and low-dimensional nanomaterials. We further demonstrate battery-powered, integrated wearable electrocardiogram (ECG) and pulse sensors that can amplify human physiological signal by 900 times with high fidelity. The sensors are capable of detecting weak ECG waves (undetectable even by clinical equipment) and diagnosing arrhythmia and atrial fibrillation. Our sub-thermionic OTFT is promising for battery/wireless powered yet performance demanding applications such as electronic skins and radio-frequency identification tags, among many others., Exploiting negative capacitance effects in organic thin-film transistors (OTFTs) is advantageous for enhancing device performance. Here, the authors report solution-processed sub-thermionic OTFTs and circuits with ferroelectric hafnium oxides that show ultra-low power and ultra-high gain.

2D semiconductors are considered to be one of the most promising channel materials to extend transistor scaling. However, the integration of ultra-thin dielectrics on 2D semiconductors has been challenging, and the reliability has not been investigated to date. Here, using monolayer 3,4,9,10-perylenetetracarboxylic dianhydride (PTCDA) molecules as interface layer, we realize EOT as low as 1.7 nm on large-area monolayer CVD MoS 2 . The reliability of ultrathin high-κ dielectric on 2D semiconductors is systematically studied for the first time. The median breakdown (BD) field of HfO 2 /PTCDA stack is over 8.42 MV/cm, which is two times that of HfO 2 /Si under the same EOT. Through TDDB we project that the gate dielectric can work reliably for 10 years under E BD = 6.5 MV/cm, which shows 85% improvement than HfO 2 /Si. The BD current increase rate in our gate stack is several orders of magnitude smaller than HfO 2 /Si. The excellent reliability suggests that molecular interfacial layer is a promising dielectric technology for 2D electronics.

Van der Waals (vdW) heterojunctions based on two-dimensional (2D) atomic crystals have been extensively studied in recent years. Herein, we show that both vertical and lateral vdW heterojunctions can be realized with layered molecular crystals using a two-step physical vapor transport (PVT) process. Both types of heterojunctions show clean and sharp interfaces without phase mixing under atomic force microscopy (AFM). They also exhibit a strong interfacial built-in electric field similar to that of their inorganic counterparts. These heterojunctions have greater potential for device applications than individual materials. The lateral heterojunction (LHJ) devices show rectifying characteristics due to the asymmetric energy barrier for holes at the interface, while the vertical heterojunction (VHJ) devices behave like metal–insulator–semiconductor tunnel junctions, with pronounced negative differential conductance (NDC). Our work extends the concept of vdW heterojunctions to molecular materials, which can be generalized to other layered organic semiconductors (OSCs) to obtain new device functionalities.

The electrical performance of two dimensional transitional metal dichalcogenides (TMDs) is strongly influenced by the amount of structural defects inside. In this work, we provide an optical spectroscopic characterization approach to correlate the amount of structural defects and the electrical performance of WSe2 devices. Low temperature photoluminescence (PL) spectra of electron beam lithography (EBL) processed WSe2 presents a clear defect-induced PL emission due to excitons bound to defects, which would strongly degrade the electrical performance. By adopting an e-beam-free transfer-electrode technique, we are able to prepare backgated WSe2 device with limited amount of defects. A maximum hole-mobility of about 200 cm2/Vs was achieved due to reduced scattering sources, which is the highest reported value among its type. This work would not only provide a versatile and nondestructive method to monitor the defects in TMDs, but also a new route to approach the room temperature phonon-limited mobility in high performance TMDs devices., Comment: 22 pages, 10 figures, to appear in Nano Research

Phase transition from the semiconducting hexagonal (2H) phase to the metallic monoclinic (1T') phase in two-dimensional (2D) transition metal dichalcogenides like MoTe

Phase transition from the semiconducting hexagonal (2H) phase to the metallic monoclinic (1T') phase in two-dimensional (2D) transition metal dichalcogenides like MoTe2 is not only of great importance in fundamental study but also of technological significance for broad device applications. Here we report a universal, facile, scalable and reversible phase engineering technique (between 2H and 1T' phases) for both monolayer and few-layer MoTe2 based on a soft hydrogen plasma treatment. The 2H → 1T' transition was confirmed by a series of characterizations including Raman spectra and mapping studies, XPS analysis and FET device measurements at varying temperatures. We attribute the phase transition to the warping of Te-Mo bonds and the lateral sliding of the top Te-layer induced by the soft hydrogen ion bombardment according to both the structural and electronic characterizations as well as the horizontal comparison with the cases of Ar or O2 plasma treatment. We have also prepared a 2D heterostructure containing periodical 2H and 1T' MoTe2 and showed that such phase transition can be readily reversed by post annealing. These results thus provide a robust and efficient approach for the phase engineering of monolayer and few-layer MoTe2 and could aid the development of 2D optoelectronic, memory and reconfigurable devices.

Negative transconductance (NTC) refers to the phenomenon of the N-shape transfer characteristic appearing with a current peak and valley. It has been extensively studied in the past few decades due to its applications in logic and memory devices. Here, we observe unique antibipolar transfer characteristics and NTC behavior in multi-layer 2,6-diphenyl anthracene organic thin-film transistors grown on h-BN, which is due to the vertical potential barrier between the charge accumulation region near the substrate and the neutral bulk region under the contacts. The applied extrinsic electric field could effectively modulate the barrier height, resulting in a competition for charge carrier transport between lateral and vertical directions. Based on the NTC and antibipolar properties, a frequency doubler has been fabricated on a single transistor, which provides a new building block for organic logic circuits.