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Semiconductor nanocrystals represent a promising class of solution-processable optical-gain media that can be manipulated via inexpensive, easily scalable colloidal techniques. Due to their extremely small sizes (typically

Realization of electrically pumped lasing with solution processable materials will have a revolutionary impact on many disciplines including photonics, chemical sensing, and medical diagnostics. Due to readily tunable, size-controlled emission wavelengths, colloidal semiconductor quantum dots (QDs) are attractive materials for attaining this goal. Here we use specially engineered QDs to demonstrate devices that operate as both a light emitting diode (LED) and an optically pumped laser. These structures feature a distributed feedback resonator integrated into a bottom LED electrode. By carefully engineering a refractive-index profile across the device, we are able to obtain good confinement of a waveguided mode within the QD medium, which allows for demonstrating low-threshold lasing even with an ultrathin (about three QD monolayers) active layer. These devices also exhibit strong electroluminescence (EL) under electrical pumping. The conducted studies suggest that the demonstrated dual-function (lasing/EL) structures represent a promising device platform for realizing colloidal QD laser diodes., Solution processable, electrically pumped lasers are a sought-after technology for many applications. Here the authors present dual-function devices based on colloidal quantum dots that behave as both electroluminescence structures and optically pumped lasers as a potential platform for electrically pumped quantum dot lasers.

The emerging technology of colloidal quantum dot electronics provides an opportunity for combining the advantages of well-understood inorganic semiconductors with the chemical processability of molecular systems. So far, most research on quantum dot electronic devices has focused on materials based on Pb- and Cd chalcogenides. In addition to environmental concerns associated with the presence of toxic metals, these quantum dots are not well suited for applications in CMOS circuits due to difficulties in integrating complementary n- and p-channel transistors in a common quantum dot active layer. Here, we demonstrate that by using heavy-metal-free CuInSe2 quantum dots, we can address the problem of toxicity and simultaneously achieve straightforward integration of complimentary devices to prepare functional CMOS circuits. Specifically, utilizing the same spin-coated layer of CuInSe2 quantum dots, we realize both p- and n-channel transistors and demonstrate well-behaved integrated logic circuits with low switching voltages compatible with standard CMOS electronics., Designing efficient toxic-element-free technologies in solution-processable CMOS electronics remains a challenge. Here, the authors demonstrate integrated logic CMOS circuits based on heavy-metal-free colloidal CuInSe2 quantum dots with low switching voltages and with degradation-free performance on month-long time scales.

Interface engineering for the improved injection properties of all-solution-processed n-type organic field-effect transistors (OFETs) arising from the use of an inkjet-printed ZnO electron injection layer were demonstrated. The characteristics of ZnO in terms of electron injection and transport were investigated, and then we employed ZnO as the electron injection layer via inkjet-printing during the fabrication of all-solution-processed, n-type OFETs. With the inkjet-printed ZnO electron injection layer, the devices exhibited approximately five-fold increased mobility (0.0058 cm2/V s to 0.030 cm2/V s), more than two-fold increased charge concentration (2.76 × 1011 cm−2 to 6.86 × 1011 cm−2), and two orders of magnitude reduced device resistance (120 MΩ cm to 3 MΩ cm). Moreover, n-type polymer form smoother film with ZnO implying denser packing of polymer, which results in higher mobility.

A recent study has shown that the use of a semiconducting surfactant in hybrid bulk heterojunction solar cells based on poly[2-methoxy-5-(3′,7′-dimethyloctyloxyl)-1,4-phenylene vinylene] and zinc oxide significantly increases their performance. To further study the mechanism underlying the improved performance resulting from the addition of a semiconducting surfactant, we compared the temperature and light intensity dependence of the current voltage characteristics and impedance spectra of devices that used no surfactant, an insulating oleic acid (OA) surfactant, or a semiconducting 2-(2-ethylhexyl)-1,3-dioxo-2,3-dihydro-1H-benzo[de]isoquinoline-6,7-dicarboxylic acid (BQ) surfactant. The temperature and light intensity dependence data enabled us to extract the activation energy for different devices, and we measured the junction resistance through impedance spectroscopy. The device that used BQ had significantly lower activation energy (9–12 meV) than that without surfactant or oleic acid (17–21 meV), thus indicating improved charge transport and consequently an increased short-circuit current. Furthermore, the impedance characteristics showed that the injection resistance, when the BQ surfactant was used, was lower than that when no surfactant or oleic acid was used. These experiments provide further evidence that the use of semiconducting surfactants is essential to improve the performance of hybrid bulk heterojunction solar cells.

We have investigated the possibility of fabricating quantum dot light-emitting diodes (QLEDs) using inkjet printing technology, which is the most attractive method for the full-color patterning of QLED displays. By controlling the quantum dot (QD) ink formulation and inkjet printing condition, we successfully patterned QLED pixels in the 60-in ultrahigh definition TV format, which has a resolution of 73 pixels per inch. The inkjet-printed QLEDs exhibited a maximum luminance of 2500 cd/m2. Although the performance of inkjet-printed QLEDs is low compared with that of QLEDs fabricated using the spin-coating process, our results clearly indicate that the inkjet printing technology is suitable for patterning QD emissive layers to realize high-resolution, full-color QLED displays.

High-efficiency organic photovoltaics (OPV) with a PTB7: PC70BM photoabsorption layer were fabricated by adopting Li- and Cd-doped ZnO electron extraction layers. For devices with both Li- and Cd-doped ZnO, the performances were significantly improved, including the short-circuit current, open-circuit voltage, fill factor (FF), and power conversion efficiency. Furthermore, film characterization with techniques including X-ray diffraction, high-resolution transmission electron microscopy, and resistivity analysis was performed. The results suggest that the improved electrical properties of Li- and Cd-doped ZnO electron extraction layers with a doping ratio of approximately 6 at% are highly effective in achieving a power conversion efficiency of up to 8%.

Large hysteresis behaviors on molybdenum disulfide (MoS2) field-effect transistors (FETs) without passivation have been typically observed, which can be one of the obstacles to understanding the intrinsic properties of MoS2 layers. Reported herein is the fact that the negligible hysteresis gap of MoS2 can be achieved through thermal annealing without any further passivation layer. The hysteresis gap of the MoS2 FETs with thermal annealing was reduced to 0.08 V, and the device showed good field-effect mobility (23.3 cm2/V s) and a high on-to-off ratio (∼107). The hysteresis-free MoS2 FETs were systematically investigated by analyzing both the contact property and the bias stability. Furthermore, low contact resistance (6.21 Ω cm) and excellent bias stability with a 1.29 × 108 sec relaxation time were obtained.

We report the improved oscillation frequency of the organic complementary ring oscillators by balancing mobilities of p- and n-type organic field-effect transistors (OFETs) with a functional polymer interfacial layer. By employing poly (methyl methacrylate) (PMMA) as the interfacial layer, the balanced performance of the p- and n-type OFETs was achieved, which resulted in the improved performance of the complementary inverters. With the PMMA interfacial layer, the noise margin was increased from 35 % to 80 % of 1/2 supply voltage, and the maximum gain was 1.5 times higher than the one of the complementary inverter without the interfacial layer. The oscillation frequency of the organic complementary ring oscillators was remarkably improved from 106.7 Hz to 1.4 kHz. The polymer interfacial layer to balance the performance of p- and n-type OFETs is found to be a simple and efficient way to facilitate the operation of the organic complementary ring oscillators.

Switching on quantum dot lasers The optical properties of quantum dots can be tailored with alterations to their size and composition. Developing quantum dots as low-threshold laser sources requires overcoming problems associated with carrier recombination and stability. Kozlov et al. report success in this direction by demonstrating that a mix of processing and postsynthesis charging can overcome these problems. Synthesis of compositionally graded core-shell quantum dots followed by a carrier charging step provides stable, low-threshold lasing. Science , this issue p. 672

The performance of colloidal quantum dot light-emitting diodes (QD-LEDs) have been rapidly improved since metal oxide semiconductors were adopted for an electron transport layer (ETL). Among metal oxide semiconductors, zinc oxide (ZnO) has been the most generally employed for the ETL because of its excellent electron transport and injection properties. However, the ZnO ETL often yields charge imbalance in QD-LEDs, which results in undesirable device performance. Here, to address this issue, we introduce double metal oxide ETLs comprising ZnO and tin dioxide (SnO2) bilayer stacks. The employment of SnO2 for the second ETL significantly improves charge balance in the QD-LEDs by preventing spontaneous electron injection from the ZnO ETL and, as a result, we demonstrate 1.6 times higher luminescence efficiency in the QD-LEDs. This result suggests that the proposed double metal oxide ETLs can be a versatile platform for QD-based optoelectronic devices.

We demonstrated modulation of charge carrier densities in all-solution-processed organic field-effect transistors (OFETs) by modifying the injection properties with self-assembled monolayers (SAMs). The all-solution-processed OFETs based on an n-type polymer with inkjet-printed Ag electrodes were fabricated as a test platform, and the injection properties were modified by the SAMs. Two types of SAMs with different dipole direction, thiophenol (TP) and pentafluorobenzene thiol (PFBT) were employed, modifying the work function of the inkjet-printed Ag (4.9 eV) to 4.66 eV and 5.24 eV with TP and PFBT treatments, respectively. The charge carrier densities were controlled by the SAM treatment in both dominant and non-dominant carrier-channel regimes. This work demonstrates that control of the charge carrier densities can be efficiently achieved by modifying the injection property with SAM treatment; thus, this approach can achieve polarity conversion of the OFETs.

In this study, we investigated the effect of the donor/acceptor mixing ratio and the substrate temperature (T(SUB)) during the co-deposition process on the performance of bulk heterojunction organic photovoltaic cells. We found that the ratio of dispersed donor islands (less than 10 nm), which hinders charge carrier transport, increased as the donor concentration (C(D)) increased in the film processed at room temperature. By contrast, the donor cluster (larger than 10 nm), providing percolation paths for the carriers, was enlarged in the film containing a high C(D) fabricated at high T(SUB) (70 degrees C). This enhanced phase separation in the mixed layer led to an improved fill factor and a decreased activation energy of the short-circuit current (J(SC)). Therefore, we demonstrated a 23% improvement in the device performance by employing an elevated T(SUB) and optimized mixing ratio in comparison with the device fabricated at room temperature.

In recent past, for next-generation device opportunities such as sub-10 nm channel field-effect transistors (FETs), tunneling FETs, and high-end display backplanes, tremendous research on multilayered molybdenum disulfide (MoS2 ) among transition metal dichalcogenides has been actively performed. However, nonavailability on a matured threshold voltage control scheme, like a substitutional doping in Si technology, has been plagued for the prosperity of 2D materials in electronics. Herein, an adjustment scheme for threshold voltage of MoS2 FETs by using self-assembled monolayer treatment via octadecyltrichlorosilane is proposed and demonstrated to show MoS2 FETs in an enhancement mode with preservation of electrical parameters such as field-effect mobility, subthreshold swing, and current on-off ratio. Furthermore, the mechanisms for threshold voltage adjustment are systematically studied by using atomic force microscopy, Raman, temperature-dependent electrical characterization, etc. For validation of effects of threshold voltage engineering on MoS2 FETs, full swing inverters, comprising enhancement mode drivers and depletion mode loads are perfectly demonstrated with a maximum gain of 18.2 and a noise margin of ≈45% of 1/2 VDD . More impressively, quantum dot light-emitting diodes, driven by enhancement mode MoS2 FETs, stably demonstrate 120 cd m-2 at the gate-to-source voltage of 5 V, exhibiting promising opportunities for future display application.

Pentacene diodes with 2,3,4,5,6-pentafluorobenzenethiol-coated Au anodes show high current densities of 100 A cm−2 at 3 V with rectification ratios of 107. Using such diodes in rectifier circuits allows an output voltage of 3.8 V to be achieved from a 10 V sinusoidal input at 1 GHz.

The stabilization and control of the electrical properties in solution-processed amorphous-oxide semiconductors (AOSs) is crucial for the realization of cost-effective, high-performance, large-area electronics. In particular, impurity diffusion, electrical instability, and the lack of a general substitutional doping strategy for the active layer hinder the industrial implementation of copper electrodes and the fine tuning of the electrical parameters of AOS-based thin-film transistors (TFTs). In this study, the authors employ a multifunctional organic-semiconductor (OSC) interlayer as a solution-processed thin-film passivation layer and a charge-transfer dopant. As an electrically active impurity blocking layer, the OSC interlayer enhances the electrical stability of AOS TFTs by suppressing the adsorption of environmental gas species and copper-ion diffusion. Moreover, charge transfer between the organic interlayer and the AOS allows the fine tuning of the electrical properties and the passivation of the electrical defects in the AOS TFTs. The development of a multifunctional solution-processed organic interlayer enables the production of low-cost, high-performance oxide semiconductor-based circuits.

A high-gain complementary metal-oxide-semiconductor (CMOS) logic inverter was implemented by fabricating p- and n-type field effect transistors (FETs) based on multi-layer WSe2 on the same wafer. Au as a high work-function metal is contacted to WSe2 for the source/drain of the p-type FET. The n-type FET has an Al electrode contacted to WSe2 for the source/drain. Both FETs were designed to have similar on-current densities (>10−7 A μm−1) and high on/off current ratios (>106). The inverter shows excellent switching characteristics including relatively high voltage gains (>25) and high noise margins (>0.9) in the range of supply voltage from 2 V to 8 V. This work has a great significance in the realization of a CMOS logic gate based on WSe2 without an additional doping scheme.