Organic Electrochemical Transistor Based on Hydrophobic Polymer Tuned by Ionic Gels.

Hydrophobic conjugated polymers have poor ionic transport property, so hydrophilic side chains are often grafted for their application as organic electrochemical transistors (OECTs). However, this modification lowers their charge transport ability. Here, an ionic gel interfacial layer is applied to improve the ionic transport while retaining the charge transport ability of the polymers. By using the ionic gels comprising gel matrix and ionic liquids as the interfacial layers, the hydrophobic polymer achieves the OECT feature with high transconductance, low threshold voltage, high current on/off ratio, short switching time, and high operational stability. The working mechanism is also revealed. Moreover, the OECT performance can be tuned by varying the types and ratios of ionic gels. With the proposed ionic gel strategy, OECTs can be effectively realized with hydrophobic conjugated polymers.

Optimizing the Photovoltaic Performance of Organic Solar Cells for Indoor Light Harvesting.

Organic solar cells (OSCs) harvesting indoor light are highly promising for emerging technologies, such as internet of things. Herein, the photovoltaic performance of PTB7-Th:PC71 BM solar cells constructed using "optimized (with 1,8-diiodooctane (DIO))" and "non-optimized (without DIO)" processing conditions are compared for indoor and outdoor applications. We find that in comparison to the "optimized" solar cell, the "non-optimized" solar cell is less efficient under simulated solar light illumination (100 mW cm-2 , spectral range 350-1100 nm), owing to significant bimolecular charge carrier recombination losses. However, under simulated indoor illumination (3.28 mW cm-2 , spectral range 400-700 nm), bimolecular recombination losses are effective suppressed, thus the power conversion efficiency of the solar cell without DIO was increased to 14.7 %, higher than that of the solar cell with DIO (14.2 %). These results suggest that the common strategy used to optimize the OSCs could be undesired for indoor OSCs. We demonstrate that the efforts for realizing the desired "morphology" of the active layer for the outdoor OSCs may be unnecessary for indoor OSCs, allowing us to realize high-efficiency indoor OSCs using a non-halogenated solvent.

Multi-model driven by diverse precipitation datasets increases confidence in identifying dominant factors for runoff change in a subbasin of the Qaidam Basin of China.

Quantifying the climatic and anthropogenic effects on hydrological processes has received considerable attention. However, diverse conclusions could be drawn when different models and forcing datasets are used. This is particularly uncertain and challenging in poorly gauged arid regions. Here we aim to tackle this issue in the poorly gauged Xiangride River Basin within the Qaidam Basin, one of the three prominent inland basins in China. We applied two distinct models (Budyko Mezentsev-Choudhurdy-Yang and process-based SWAT) to a poorly-gauged inland basin in West China. The model simulations were driven by four precipitation products including Tropical Rainfall Measuring Mission (TRMM) 3B42 V7, Global Precipitation Measurement (GPM) IMERG V6, Multi-Source Weighted-Ensemble Precipitation (MSWEP) and China Meteorological Assimilation Driving Datasets (CMADS). Our results indicate that MSWEP performed best (NSE = 0.64 vs. 0.36-0.59 for other datasets) in the baseline period (2009-2012), whereas CMADS was more accurate during the impacted period (2013-2016); CMADS and GPM might underestimate the precipitation in the baseline and impacted period, respectively. Hydrological processes during the impacted period are presumed to be influenced by climate variation and/or human activities, compared to the relatively natural status in the baseline period. We conclude that runoff decline between the two periods was mainly affected by human activities (-66 to 94%), whereas the contribution of climate variation was more likely positive. A literature survey reveals that major anthropogenic effects in the study area includes reservoir, road construction and cropland expansion that could lead to runoff decrease. We recommend the use of process-based model (e.g., SWAT) in studies like this, as process-based models driven by high-quality remote-sensed or reanalysis climate datasets, better represents the spatiotemporal hydrological change under altered conditions, whereas the steady-state assumption of soil water for the Budyko model may not be fully satisfied during a short period.

Applicability analysis of multiple precipitation products in the Qaidam Basin, Northwestern China.

In the Qaidam Basin, meteorological stations are sparsely distributed, and the observational precipitation data are therefore not comprehensive, which significantly hampers the accurate assessment and optimal allocation of regional water resources. This study aims to evaluate the accuracy of three precipitation products (MSWEP V2, GPM IMERG V6, and TRMM 3B43) against gauged-based precipitation data from nine meteorological stations and 12 hydrologic stations in the Qaidam Basin from 2001 to 2016. The results reveal the following: (1) At the annual and monthly scales, the MSWEP product has the highest accuracy, followed by the GPM product. However, the TRMM product only reveals a correlation at the monthly scale; (2) the MSWEP product performs better in the wet season than the dry season, and the TRMM product has an abnormally high value of precipitation in the wet season. Moreover, it was shown that the accuracy of the GPM product is superior to that of the TRMM product; however, it has a low detection capability in some mountainous areas; and (3) the average error of each precipitation product at the meteorological stations is smaller than that at the hydrological stations.

Regiocontrolled dimerization of asymmetric diazaheptacene derivatives toward X-shaped porous semiconductors.

Conformationally rigid X-shaped PAHs are attracting interest due to their self-assembly into unique networks and as models to study through-space exciton and charge delocalization in one single molecule. We report here the synthesis of X-shaped PAHs by dimerization of diazaheptacene diimides. The diimide groups are employed to effectively direct the self-assembly into antiparallel dimer aggregates, which assist the compounds to undergo a regiocontrolled [4 + 4] dimerization, leading to an X-shaped conformation bearing electron-poor and -rich subunits. The resulting PAHs are found to pack in 2D layers with large open channels and infinite π⋯π arrays. Furthermore, these highly crystalline porous materials serve as electron-transporting materials in OFETs due to the long-range π-stacked arrays in the layers. This work presents a potentially generalizable strategy, which may provide a unique class of porous semiconductors for organic devices, taking advantage of their open channels.

Isomeric Pyrenodithiophenediones and Their Derivatives: Synthesis, Reactivity, and Device Performance.

Two isomeric pyrenodithiophenediones and their triisopropylsilyl(TIPS)-ethynyl-functionalized derivatives were synthesized and characterized. With treatment of excess lithium TIPS-acetylide, the isomeric diones could undergo Michael and carbonyl additions to form three derivatives with four, three, and two TIPS-ethynyl groups, respectively. The isomeric TIPS-ethynyl-functionalized derivatives show different physicochemical properties. The single-crystalline transistors based on TIPS-ethynyl-functionalized derivatives exhibit a promising p-type transport behavior, with hole mobilities up to 0.51 cm2 V-1 s-1.

Tuning the electronic properties of thiophene-annulated NDIs: the influence of the lateral fusion position.

A new asymmetric thiophene-annulated NDI (NTTI) has been designed and synthesized. NTTI exhibits an enhanced polarized electronic structure relative to the symmetric analogue (NDTI). The fusion position of thiophene affects the optical, electrochemical, and charge transport properties. The OFET device based on single crystalline microribbons of C8-NTTI shows an electron mobility up to 1.47 cm2 V-1 s-1.

N-Heterocyclic-Carbene-Treated Gold Surfaces in Pentacene Organic Field-Effect Transistors: Improved Stability and Contact at the Interface.

N-Heterocyclic carbenes (NHCs), which react with the surface of Au electrodes, have been successfully applied in pentacene transistors. With the application of NHCs, the charge-carrier mobility of pentacene transistors increased by five times, while the contact resistance at the pentacene-Au interface was reduced by 85 %. Even after annealing the NHC-Au electrodes at 200 °C for 2 h before pentacene deposition, the charge-carrier mobility of the pentacene transistors did not decrease. The distinguished performance makes NHCs as excellent alternatives to thiols as metal modifiers for the application in organic field-effect transistors (OFETs).

Exciton Coupling of Merocyanine Dyes from H- to J-type in the Solid State by Crystal Engineering.

A key issue for the application of π-conjugated organic molecules as thin film solid-state materials is the packing structure, which drastically affects optical and electronic properties due to intermolecular coupling. In this regard, merocyanine dyes usually pack in H-coupled antiparallel arrangements while structures with more interesting J-type coupling have been rarely reported. Here we show that for three highly dipolar merocyanine dyes, which exhibit the same π-scaffold and accordingly equal properties as monomers in solution, the solid-state packing can be changed by a simple variation of aliphatic substituents to afford narrow and intense absorption bands with huge hypsochromic (H) or bathochromic (J) shifts for their thin films and nanocrystals. Time-dependent density functional theory calculations show that the energetic offset of almost 1 eV magnitude results from distinct packing motifs within the crystal structures that comply with the archetype H- or J-aggregate structures as described by Kasha's exciton theory.

Gas Sensors Based on Polymer Field-Effect Transistors.

This review focuses on polymer field-effect transistor (PFET) based gas sensor with polymer as the sensing layer, which interacts with gas analyte and thus induces the change of source-drain current (ΔISD). Dependent on the sensing layer which can be semiconducting polymer, dielectric layer or conducting polymer gate, the PFET sensors can be subdivided into three types. For each type of sensor, we present the molecular structure of sensing polymer, the gas analyte and the sensing performance. Most importantly, we summarize various analyte-polymer interactions, which help to understand the sensing mechanism in the PFET sensors and can provide possible approaches for the sensor fabrication in the future.

Investigation into the Sensing Process of High-Performance H2S Sensors Based on Polymer Transistors.

Herein a H2S sensor based on a polymer field-effect transistor is reported and the sensor shows high sensitivity, excellent selectivity, fast response, and good operational stability. A concentration as low as 1 ppb H2 is detectable, which is to date the most sensitive H2S sensor based on organic semiconducting film. Thinning the thickness of active layer does not necessarily improve the sensitivity, but rather leads to the reduction of performance if the thickness is too low. Further analysis proposes a mechanism that the changing rate of absorption and desorption of H2S molecules is different when the thickness of active layer varies, indicating the necessity for thickness optimization.

Head-to-Tail Zig-Zag Packing of Dipolar Merocyanine Dyes Affords High-Performance Organic Thin-Film Transistors.

Attachment of bulky substituents at both thiophene donor (D) and thiazole acceptor (A) heterocycles of a dipolar (µ(g)=10.4 D) D-π-A merocyanine dye affords a more than 1 Šexpansion of the common antiparallel supramolecular dimer motif in the solid state, enabling very close π-contacts (3.36 Å) to two other neighbor molecules on each of the two remaining π-faces. This unusual packing motif leads to three-dimensional percolation pathways for hole transport and affords thin-film transistors with mobility up to 0.64 cm(2) V(-1) s(-1).

Integrated prototype nanodevices via SnO2 nanoparticles decorated SnSe nanosheets.

Hybrid materials made from all inorganic components are intriguing in many fields, because they have shown in-depth potential use for electronic and optoelectronic applications including solar cells, gas sensors, photodetectors, and field effect transistors. Hybrid materials made from SnO2 nanoparticles on SnSe nanosheets have been synthesized via a facile, lost-cost and safe solution method, and have been demonstrated as promising multifunctional materials in various prototype devices, including gas sensors, photodetectors, and field effect transistors.

High performance n-type single crystalline transistors of naphthalene bis(dicarboximide) and their anisotropic transport in crystals.

High-performance n-type organic single crystal transistors of a naphthalene diimide are demonstrated. The accomplished transistors exhibit electron mobility as high as 0.7 cm(2) V(-1) s(-1). The anisotropic charge transport in the elongated hexagonal crystals of the naphthalene diimide is also explored. The transport anisotropy along different directions is at least 1.6 (mobility ratio).

Hybrid rylene arrays via combination of Stille coupling and C-H transformation as high-performance electron transport materials.

Hybrid rylene arrays have been prepared via a combination of Stille coupling and C-H transformation. The ability to extend the π system along the equatorial axis of rylenes not only leads to broadened light absorption but also increases the electron affinity, which can facilitate electron injection and transport with ambient stability.

One-pot synthesis of well-defined oligo- butadiynylene-naphthalene diimides.

A homogeneous series of well-defined oligo-butadiynylene-NDIs containing up to five naphthalene diimides (NDIs) moieties have been efficiently synthesized in one pot by oxidative homocoupling of 1,6-di((trimethylsilyl)ethynyl)naphthalene diimides in good yields.

Squaramide-catalyzed enantioselective Friedel-Crafts reaction of indoles with imines.

Chiral squaramides are highly enantioselective catalysts for Friedel-Crafts reaction of indoles with N-tosyl imines, affording 3-indolyl methanamine products in 85-96% yields and 84-96% ees.