High Mobility Anisotropic Black Phosphorus Nanoribbon Field‐Effect Transistor

Achieving excellent electrostatic control and immunity to short channel effects are the formidable challenges in ultrascaled devices. 3D device architectures, such as nanoribbon, have successfully mitigated these problems by achieving uniform top‐ and side‐wall control of the channel. Here, by leveraging on the merits of 3D structure, high‐mobility black phosphorus nanoribbon field‐effect transistors (BPNR‐FET) are demonstrated and the anisotropic transport properties are systematically investigated. A simple top‐down reactive ion etching method is used to realize both armchair‐ and zigzag‐oriented nanoribbons with various widths down to 60 nm. The mobility of BPNR‐FET is found to be width‐ and thickness‐dependent, with the highest hole mobility of ≈862 cm² V^?1 s^?1 demonstrated in armchair‐oriented device at room temperature by combining high‐κ gate dielectric and hydrogen treatment to reduce sidewall scattering. Furthermore, hydrogenation effectively passivates the nanoribbon dangling bonds, leading to hysteresis and contact resistance improvement. This work unravels the superior electrical performance underscore a conceptually new device based on BP nanoribbons, paving the way toward the development of nonplanar devices on 2D materials platform.     

High‐Performance,Air‐Stable,Top‐Gate,p‐Channel WSe2 Field‐Effect Transistor with Fluoropolymer Buffer Layer

High‐performance, air‐stable, p‐channel WSe₂ top‐gate field‐effect transistors (FETs) using a bilayer gate dielectric composed of high‐ and low‐k dielectrics are reported. Using only a high‐k Al₂O₃ as the top‐gate dielectric generally degrades the electrical properties of p‐channel WSe₂, therefore, a thin fluoropolymer (Cytop) as a buffer layer to protect the 2D channel from high‐k oxide forming is deposited. As a result, a top‐gate‐patterned 2D WSe₂ FET is realized. The top‐gate p‐channel WSe₂ FET demonstrates a high hole mobility of 100 cm²_­ V^?1 s^?1 and a I_ON/I_OFF ratio > 10⁷ at low gate voltages (V_GS ca. ?4 V) and a drain voltage (V_DS) of ?1 V on a glass substrate. Furthermore, the top‐gate FET shows a very good stability in ambient air with a relative humidity of 45% for 7 days after device fabrication. Our approach of creating a high‐k oxide/low‐k organic bilayer dielectric is advantageous over single‐layer high‐k dielectrics for top‐gate p‐channel WSe₂ FETs, which will lead the way toward future electronic nanodevices and their integration.     

Synthesis,Morphology, and Properties of Poly(3‐hexylthiophene)‐block‐Poly(vinylphenyl oxadiazole) Donor–Acceptor Rod–Coil Block Copolymers and Their Memory Device Applications

Novel donor–acceptor rod–coil diblock copolymers of regioregular poly(3‐hexylthiophene) ( P3HT )‐block‐poly(2‐phenyl‐5‐(4‐vinylphenyl)‐1,3,4‐oxadiaz‐ole) ( POXD ) are successfully synthesized by the combination of a modified Grignard metathesis reaction ( GRIM ) and atom transfer radical polymerization ( ATRP ). The effects of the block ratios of the P3HT donor and POXD pendant acceptor blocks on the morphology, field effect transistor mobility, and memory device characteristics are explored. The TEM, SAXS, WAXS, and AFM results suggest that the coil block fraction significantly affects the chain packing of the P3HT block and depresses its crystallinity. The optical absorption spectra indicate that the intramolecular charge transfer between the main chain P3HT donor and the side chain POXD acceptor is relatively weak and the level of order of P3HT chains is reduced by the incorporation of the POXD acceptor. The field effect transistor (FET) hole mobility of the system exhibits a similar trend on the optical properties, which are also decreased with the reduced ordered P3HT crystallinity. The low‐lying highest occupied molecular orbital (HOMO) energy level (–6.08 eV) of POXD is employed as charge trap for the electrical switching memory devices. P3HT‐ b ‐POXD exhibits a non‐volatile bistable memory or insulator behavior depending on the P3HT / POXD block ratio and the resulting morphology. The ITO/ P3HT₄₄ ‐b‐ POXD₁₈ /Al memory device shows a non‐volatile switching characteristic with negative differential resistance (NDR) effect due to the charge trapped POXD block. These experimental results provide the new strategies for the design of donor‐acceptor rod‐coil block copolymers for controlling morphology and physical properties as well as advanced memory device applications.     

Tunable Crystal Nanostructures of Pentacene Thin Films on Gate Dielectrics Possessing Surface‐Order Control

To enhance the electrical performance of pentacene‐based field‐effect transistors (FETs) by tuning the surface‐induced ordering of pentacene crystals, we controlled the physical interactions at the semiconductor/gate dielectric (SiO₂) interface by inserting a hydrophobic self‐assembled monolayer (SAM, CH₃‐terminal) of organoalkyl‐silanes with an alkyl chain length of C8, C12, C16, or C18, as a complementary interlayer. We found that, depending on the physical structure of the dielectric surfaces, which was found to depend on the alkyl chain length of the SAM (ordered for C18 and disordered for C8), the pentacene nano‐layers in contact with the SAM could adopt two competing crystalline phases—a “thin‐film phase” and “bulk phase” – which affected the π‐conjugated nanostructures in the ultrathin and subsequently thick films. The field‐effect mobilities of the FET devices varied by more than a factor of 3 depending on the alkyl chain length of the SAM, reaching values as high as 0.6 cm² V^?1 s^?1 for the disordered SAM‐treated SiO₂ gate‐dielectric. This remarkable change in device performance can be explained by the production of well π‐conjugated and large crystal grains in the pentacene nanolayers formed on a disordered SAM surface. The enhanced electrical properties observed for systems with disordered SAMs can be attributed to the surfaces of these SAMs having fewer nucleation sites and a higher lateral diffusion rate of the first seeding pentacene molecules on the dielectric surfaces, due to the disordered and more mobile surface state of the short alkyl SAM.     

Non‐Lithographic Fabrication of All‐2D α‐MoTe2 Dual Gate Transistors

As one of the emerging new transition‐metal dichalcogenides materials, molybdenum ditelluride (α‐MoTe₂) is attracting much attention due to its optical and electrical properties. This study fabricates all‐2D MoTe₂‐based field effect transistors (FETs) on glass, using thin hexagonal boron nitride and thin graphene in consideration of good dielectric/channel interface and source/drain contacts, respectively. Distinguished from previous works, in this study, all 2D FETs with α‐MoTe₂ nanoflakes are dual‐gated for driving higher current. Moreover, for the present 2D dual gate FET fabrications on glass, all thermal annealing and lithography processes are intentionally exempted for fully non‐lithographic method using only van der Waal's forces. The dual‐gate MoTe₂ FET displays quite a high hole and electron mobility over ≈20 cm² V^?1 s^?1 along with ON/OFF ratio of ≈10⁵ in maximum as an ambipolar FET and also demonstrates high drain current of a few tens‐to‐hundred μA at a low operation voltage. It appears promising enough to drive organic light emitting diode pixels and NOR logic functions on glass.     

Carbonyl‐β‐Cyclodextrin as a Novel Binder for Sulfur Composite Cathodes in Rechargeable Lithium Batteries

As one of the essential components in electrodes, the binder affects the performance of a rechargeable battery. By modifying β‐cyclodextrin (β‐CD), an appropriate binder for sulfur composite cathodes is identified. Through a partial oxidation reaction in H₂O₂ solution, β‐CD is successfully modified to carbonyl‐β‐cyclodextrin (C‐β‐CD), which exhibits a water solubility ca. 100 times that of β‐CD at room temperature. C‐β‐CD possesses the typical properties of an aqueous binder: strong bonding strength, high solubility in water, moderate viscosity, and wide electrochemical windows. Sulfur composite cathodes with C‐β‐CD as the binder demonstrate a high reversible capacity of 694.2 mA h g_(composite)^?1 and 1542.7 mA h g_(sulfur)^?1, with a sulfur utilization approaching 92.2%. The discharge capacity remains at 1456 mA h g_(sulfur)^?1 after 50 cycles, which is much higher than that of the cathode with unmodified β‐CD as binder. Combined with its low cost and environmental benignity, C‐β‐CD is a promising binder for sulfur cathodes in rechargeable lithium batteries with high electrochemical performance.     

Low Voltage and Ferroelectric 2D Electron Devices Using Lead‐Free BaxSr1‐xTiO3 and MoS2 Channel

Coupling between non‐toxic lead‐free high‐k materials and 2D semiconductors is achieved to develop low voltage field effect transistors (FETs) and ferroelectric non‐volatile memory transistors as well. In fact, low voltage switching ferroelectric memory devices are extremely rare in 2D electronics. Now, both low voltage operation and ferroelectric memory function have been successfully demonstrated in 2D‐like thin MoS₂ channel FET with lead‐free high‐k dielectric Ba_xSr_1‐xTiO₃ (BST) oxides. When the BST surface is coated with a 5.5‐nm‐ultrathin poly(methyl methacrylate) (PMMA)‐brush for improved roughness, the MoS₂ FET with BST (x = 0.5) dielectric results in an extremely low voltage operation at 0.5 V. Moreover, the BST with an increased Ba composition (x = 0.8) induces quite good ferroelectric memory properties despite the existence of the ultrathin PMMA layer, well switching the MoS₂ FET channel states in a non‐volatile manner with a ±3 V low voltage pulse. Since the employed high‐k dielectric and ferroelectric oxides are lead‐free in particular, the approaches for applying high‐k BST gate oxide for 2D MoS₂ FET are not only novel but also practical towards future low voltage nanoelectronics and green technology.     

Nanoscale Resistive Switching in Amorphous Perovskite Oxide (a‐SrTiO3) Memristors

Memristive devices are the precursors to high density nanoscale memories and the building blocks for neuromorphic computing. In this work, a unique room temperature synthesized perovskite oxide (amorphous SrTiO₃: a‐STO) thin film platform with engineered oxygen deficiencies is shown to realize high performance and scalable metal‐oxide‐metal (MIM) memristive arrays demonstrating excellent uniformity of the key resistive switching parameters. a‐STO memristors exhibit nonvolatile bipolar resistive switching with significantly high (10³–10⁴) switching ratios, good endurance (>10⁶I–V sweep cycles), and retention with less than 1% change in resistance over repeated 10⁵ s long READ cycles. Nano‐contact studies utilizing in situ electrical nanoindentation technique reveal nanoionics driven switching processes that rely on isolatedly controllable nano‐switches uniformly distributed over the device area. Furthermore, in situ electrical nanoindentation studies on ultrathin a‐STO/metal stacks highlight the impact of mechanical stress on the modulation of non‐linear ionic transport mechanisms in perovskite oxides while confirming the ultimate scalability of these devices. These results highlight the promise of amorphous perovskite memristors for high performance CMOS/CMOL compatible memristive systems.     

Enhanced Electrochemical H2 Evolution by Few‐Layered Metallic WS2(1−x)Se2x Nanoribbons

As an effective alternative to noble platinum electrocatalyst, earth abundant and inexpensive layered transition metal dichalcogenides (TMDs) are investigated for the hydrogen evolution reaction (HER). Compared with binary TMDs, the tunably composed ternary TMDs have hitherto received relatively little attention. Here, few‐layered ternary WS_2(1?x)Se_2x nanoribbons (NRs) with metallic 1T phases, much more catalytically active in HER, are prepared for the first time. The favorable ΔG_H^o introduced by the tensile region on the surface, along with the presence of local lattice distortions of the WS_2(1?x)Se_2x nanoribbons with metallic 1T phases, greatly promotes the HER process. These ternary NRs achieve the lowest overpotential of ≈0.17 V at 10 mA cm^?2 and a Tafel slope of ≈68 mV dec^?1 at a low catalyst loading (≈0.30 ± 0.02 mg cm^?2). Notably, the long‐term durability suggests the potential of practical applications in acid electrolytes. The results here suggest that the ternary WS_2(1?x)Se_2x NRs with 1T phases are prominent alternatives to platinum‐based HER electrocatalysts.     

Short‐Chain Ligand‐Passivated Stable α‐CsPbI3 Quantum Dot for All‐Inorganic Perovskite Solar Cells

Cubic phase CsPbI₃ (α‐CsPbI₃) perovskite quantum dots (QDs) have received extensive attention due to their all‐inorganic composition and suitable band gap (1.73 eV). However, α‐CsPbI₃ QDs might convert to δ‐CsPbI₃ (orthorhombic phase with indirect band gap of 2.82 eV) due to easy loss of surface ligands. In addition, commonly used long‐chain ligands (oleic acid, OA, and oleylamine, OLA) hinder efficient charge transport in optoelectronic devices. In order to relieve these drawbacks, OA, OLA, octanoic acid, and octylamine are used as capping ligands for synthesizing high‐quality α‐CsPbI₃ QDs. The results indicate that these QDs exhibit excellent optical properties and long‐term stability compared to QDs capped only with OA and OLA. Moreover, QDs with shorter ligands exhibit an enhanced charge transport rate, which improves the power conversion efficiency of photovoltaic devices from 7.76% to 11.87%.     

Conductivity of SU‐8 Thin Films through Atomic Force Microscopy Nano‐Patterning

Processing flexibility and good mechanical properties are the two major reasons for SU‐8 extensive applicability in the micro‐fabrication of devices. In order to expand its usability down to the nanoscale, conductivity of ultra‐thin SU‐8 layers as well as its patterning by AFM are explored. By performing local electrical measurements outstanding insulating properties and a dielectric strength 100 times larger than that of SiO₂ are shown. It is also demonstrated that the resist can be nano‐patterned using AFM, obtaining minimum dimensions below 40nm and that it can be combined with parallel lithographic methods like UV‐lithography. The concurrence of excellent insulating properties and nanometer‐scale patternability enables a valuable new approach for the fabrication of nanodevices. As a proof of principle, nano‐electrode arrays for electrochemical measurements which show radial diffusion and no overlap between different diffusion layers are fabricated. This indicates the potential of the developed technique for the nanofabrication of devices.     

Fully Transparent p‐MoTe2 2D Transistors Using Ultrathin MoOx/Pt Contact Media for Indium‐Tin‐Oxide Source/Drain

Since transition metal dichalcogenide (TMD) semiconductors are found as 2D van der Waals materials with a discrete energy bandgap, many 2D‐like thin field effect transistors (FETs) and PN diodes are reported as prototype electrical and optoelectronic devices. As a potential application of display electronics, transparent 2D FET devices are also reported recently. Such transparent 2D FETs are very few in report, yet no p‐type channel 2D‐like FETs are seen. Here, 2D‐like thin transparent p‐channel MoTe₂ FETs with oxygen (O₂) plasma‐induced MoO_x/Pt/indium‐tin‐oxide (ITO) contact are reported for the first time. For source/drain contact, 60 s short O₂ plasma and ultrathin Pt‐deposition processes on MoTe₂ surface are sequentially introduced before ITO thin film deposition and patterning. As a result, almost transparent 2D FETs are obtained with a decent mobility of ≈5 cm² V^?1 s^?1, a high ON/OFF current ratio of ≈10⁵, and 70% transmittance. In particular, for normal MoTe₂ FETs without ITO, O₂ plasma process greatly improves the hole injection efficiency and device mobility (≈60 cm² V^?1 s^?1), introducing ultrathin MoO_x between Pt source/drain and MoTe₂. As a final device application, a photovoltaic current modulator, where the transparent FET stably operates as gated by photovoltaic effects, is integrated.     

Synthesis of Dumbbell‐Like Gold–Metal Sulfide Core–Shell Nanorods with Largely Enhanced Transverse Plasmon Resonance in Visible Region and Efficiently Improved Photocatalytic Activity

The metallic nanostructures with unique properties of tunable plasmon resonance and large field enhancement have been cooperated with semiconductor to construct hetero‐nanostructures for various applications. Herein, a general and facile approach to synthesize uniform dumbbell‐like gold–sulfide core–shell hetero‐nanostructures is reported. The transformation from Au nanorods (NRs) to dumbbell‐like Au NRs and coating of metal sulfide shells (including Bi₂S₃, CdS, Cu_xS, and ZnS) are achieved in a one‐pot reaction. Due to the reshaping of Au core and the deposition of sulfide shell, the plasmon resonances of Au NRs are highly enhanced, especially the about 2 times enhancement for the visible transverse plasmon resonance compared with the initial Au NRs. Owing to the highly enhanced visible light absorption and strong local electric field, we find the photocatalytic activity of dumbbell‐like Au–Bi₂S₃ NRs is largely enhanced compared with pure Bi₂S₃ and normal Au–Bi₂S₃ NRs by testing the photodegradation rate of Rhodamine B (RhB). Moreover, the second‐layer sulfide can be coated and the double‐shell Au–Bi₂S₃–CdS hetero‐nanostructures show further improved photodegradation rate, especially about 2 times than that of Degussa P25 TiO₂ (P25) ascribing to the optimum band arrangement and then the prolonged lifetime of photo‐generated carriers.     

Solution‐Processed,Alkali Metal‐Salt‐Doped,Electron‐Transport Layers for High‐Performance Phosphorescent Organic Light‐Emitting Diodes

High‐performance, blue, phosphorescent organic light‐emitting diodes (PhOLEDs) are achieved by orthogonal solution‐processing of small‐molecule electron‐transport material doped with an alkali metal salt, including cesium carbonate (Cs₂CO₃) or lithium carbonate (Li₂CO₃). Blue PhOLEDs with solution‐processed 4,7‐diphenyl‐1,10‐phenanthroline (BPhen) electron‐transport layer (ETL) doped with Cs₂CO₃ show a luminous efficiency (LE) of 35.1 cd A^?1 with an external quantum efficiency (EQE) of 17.9%, which are two‐fold higher efficiency than a BPhen ETL without a dopant. These solution‐processed blue PhOLEDs are much superior compared to devices with vacuum‐deposited BPhen ETL/alkali metal salt cathode interfacial layer. Blue PhOLEDs with solution‐processed 1,3,5‐tris(m‐pyrid‐3‐yl‐phenyl)benzene (TmPyPB) ETL doped with Cs₂CO₃ have a luminous efficiency of 37.7 cd A^?1 with an EQE of 19.0%, which is the best performance observed to date in all‐solution‐processed blue PhOLEDs. The results show that a small‐molecule ETL doped with alkali metal salt can be realized by solution‐processing to enhance overall device performance. The solution‐processed metal salt‐doped ETLs exhibit a unique rough surface morphology that facilitates enhanced charge‐injection and transport in the devices. These results demonstrate that orthogonal solution‐processing of metal salt‐doped electron‐transport materials is a promising strategy for applications in various solution‐processed multilayered organic electronic devices.     

Alkyl‐Chain‐Length‐Independent Hole Mobility via Morphological Control with Poly(3‐alkylthiophene) Nanofibers

The field‐effect transistor (FET) and diode characteristics of poly(3‐alkylthiophene) (P3AT) nanofiber layers deposited from nanofiber dispersions are presented and compared with those of layers deposited from molecularly dissolved polymer solutions in chlorobenzene. The P3AT n‐alkyl‐side‐chain length was varied from 4 to 9 carbon atoms. The hole mobilities are correlated with the interface and bulk morphology of the layers as determined by UV–vis spectroscopy, transmission electron microscopy (TEM) with selected area electron diffraction (SAED), atomic force microscopy (AFM), and polarized carbon K‐edge near edge X‐ray absorption fine structure (NEXAFS) spectroscopy. The latter technique reveals the average polymer orientation in the accumulation region of the FET at the interface with the SiO₂ gate dielectric. The previously observed alkyl‐chain‐length‐dependence of the FET mobility in P3AT films results from differences in molecular ordering and orientation at the dielectric/semiconductor interface, and it is concluded that side‐chain length does not determine the intrinsic mobility of P3ATs, but rather the alkyl chain length of P3ATs influences FET diode mobility only through changes in interfacial bulk ordering in solution processed films.     

Donor–Acceptor Poly(3‐hexylthiophene)‐block‐Pendent Poly(isoindigo) with Dual Roles of Charge Transporting and Storage Layer for High‐Performance Transistor‐Type Memory Applications

Field‐effect transistor memories usually require one additional charge storage layer between the gate contact and organic semiconductor channel. To avoid such complication, new donor–acceptor rod–coil diblock copolymers (P3HT₄₄‐b‐Piso_n) of poly(3‐hexylthiophene) (P3HT)‐block‐poly(pendent isoindigo) (Piso) are designed, which exhibit high performance transistor memory characteristics without additional charge storage layer. The P3HT and Piso blocks are acted as the charge transporting and storage elements, respectively. The prepared P3HT₄₄‐b‐Piso_n can be self‐assembled into fibrillar‐like nanostructures after the thermal annealing process, confirmed by atomic force microscopy and grazing‐incidence X‐ray diffraction. The lowest‐unoccupied molecular orbital levels of the studied polymers are significantly lowered as the block length of Piso increases, leading to a stronger electron affinity as well as charge storage capability. The field‐effect transistors (FETs) fabricated from P3HT₄₄‐b‐Piso_n possess p‐type mobilities up to 4.56 × 10^?2 cm² V^?1 s^?1, similar to that of the regioregular P3HT. More interestingly, the FET memory devices fabricated from P3HT₄₄‐b‐Piso_n exhibit a memory window ranging from 26 to 79 V by manipulating the block length of Piso, and showed stable long‐term data endurance. The results suggest that the FET characteristics and data storage capability can be effectively tuned simultaneously through donor/acceptor ratio and thin film morphology in the block copolymer system.     

Pulsed Laser Ablation Based Synthesis of PbS‐Quantum Dots‐Decorated One‐Dimensional Nanostructures and Their Direct Integration into Highly Efficient Nanohybrid Heterojunction‐Based Solar Cells

The pulsed laser deposition (PLD) technique is used for the direct fabrication of nanohybrid heterojunctions (NH‐HJs) solar cells exhibiting high PCE and excellent stability in air without any encapsulation and/or resorting to any surface treatment, ligand engineering and/or post‐synthesis processing. The NH‐HJs are achieved through the PLD‐based decoration of hydrothermally‐grown one‐dimensional TiO₂ nanorods (TiO₂‐NRs) by PbS quantum dots (PbS‐QDs). By optimizing both the amount of PbS‐QDs (via the number of laser ablation pulses) and the length of the TiO₂‐NRs, it is possible to achieve optimal NH‐HJs based PV devices with high power conversion efficiency (PCE) of 4.85%. This high PCE is found to occur for an optimal length of the NRs (≈290 nm) which coincides with the average penetration depth of PbS‐QDs into the porous TiO₂‐NRs matrix, leading thereby to the formation of the largest extent of NH‐HJs. Most importantly, the PCE of these novel devices is found to be fairly stable for several months under ambient air. The addition of single‐wall carbon nanotubes (SWCNTs) onto the TiO₂‐NRs prior to their decoration by PbS‐QDs is shown to further enhance their PCE to a value as high as 5.3%, because of additional light absorption and improved charge collection ensured by SWCNTs.     

Poly(diketopyrrolopyrrole‐benzothiadiazole) with Ambipolarity Approaching 100% Equivalency

As a characteristic feature of conventional conjugated polymers, it has been generally agreed that conjugated polymers exhibit either high hole transport property (p‐type) or high electron transport property (n‐type). Although ambipolar properties have been demonstrated from specially designed conjugated polymers, only a few examples have exhibited ambipolar transport properties under limited conditions. Furthermore, there is, as yet, no example with ‘equivalent’ hole and electron transport properties. We describe the realization of an equivalent ambipolar organic field‐effect transistor (FET) by using a single‐component visible–near infrared absorbing diketopyrrolopyrrole (DPP)‐benzothiadiazole (BTZ) copolymer, namely poly[3,6‐dithiene‐2‐yl‐2,5‐di(2‐decyltetradecyl)‐pyrrolo[3,4‐c]pyrrole‐1,4‐dione‐5’,5’’‐diyl‐alt‐benzo‐2,1, 3‐thiadiazol‐4,7‐diyl] ( PDTDPP‐alt‐BTZ ). PDTDPP‐alt‐BTZ shows not only ideally balanced charge carrier mobilities for both electrons (?_e = 0.09 cm²V^?1s^?1) and holes (?_h = 0.1 cm²V^?1s^?1) but also its inverter constructed with the combination of two identical ambipolar FETs exhibits a gain of ～35 that is much higher than usually obtained values for unipolar logic.     

Electrically conductive anti‐reflecting nanostructure for chalcogenide thin‐film solar cells

Electrically conducting aluminum (Al)‐doped ZnO nanorods (NRs) film has been introduced as an anti‐reflective (AR) layer for effective light trapping in chalcogenide thin‐film solar cells. Results indicate that the Al‐doping significantly reduced the electrical contact resistance between the Ag top electrode and the AR layer. The Al‐doped ZnO NRs exhibited low average reflectance (4.5%) over the entire visible and near‐infrared range, and changed the nature of electrical contact between the Ag electrode and the AR layer from Schottky to Ohmic. Finally, the CuInS₂ solar cell coated with the Al‐doped ZnO NRs exhibited huge enhancement in photovoltaic efficiency from 9.57% to 11.70% due to the lowering series resistance and the increase in the short‐circuit current density, when compared with that of a solar cell without the AR layer. Copyright © 2014 John Wiley & Sons, Ltd.     

Kinetically Controlled Crystallization in Conjugated Polymer Films for High‐Performance Organic Field‐Effect Transistors

Ordering of semiconducting polymers in thin films from the nano to microscale is strongly correlated with charge transport properties as well as organic field‐effect transistor performance. This paper reports a method to control nano to microscale ordering of poly{[N,N′‐bis(2‐octyldodecyl)‐naphthalene‐1,4,5,8‐bis(dicarboximide)‐2,6‐diyl]‐alt‐5,5′‐(2,2′‐bithiophene)} (P(NDI2OD‐T2)) thin films by precisely regulating the solidification rate from the metastable state just before crystallization. The proposed simple but effective approach, kinetically controlled crystallization, achieves optimized P(NDI2OD‐T2) films with large polymer domains, long range ordered fibrillar structures, and molecular orientation preferable for electron transport leading to dramatic morphological changes in both polymer domain sizes at the micrometer scale and molecular packing structures at nanoscales. Structural changes significantly increase electron mobilities up to 3.43 ± 0.39 cm² V^?1 s^?1 with high reliability, almost two orders of enhancement compared with devices from naturally dried films. Small contact resistance is also obtained for electron injection (0.13 MΩ cm), low activation energy (62.51 meV), and narrow density of states distribution for electron transport in optimized thin films. It is believed that this study offers important insight into the crystallization of conjugated polymers that can be broadly applied to optimize the morphology of semiconducting polymer films for solution processed organic electronic devices.