STM Lithography in an Organic Self‐Assembled Monolayer

We describe the suitability of ultra‐high vacuum scanning tunneling microscopy (UHV‐STM) based nanolithography by using highly ordered monomolecular organic films, called self‐assembled monolayers (SAMs), as ultrathin resists. Organothiol‐type SAMs such as hexadecanethiol (SH–(CH₂)₁₅–CH₃) and N‐biphenylthiol (SH–(C₆H₆)₂–NO₂) monolayers have been prepared by immersion on gold films and Au(111) single crystals. Organosilane‐type SAMs such as octadecyltrichlorosilane (SiCl₃–(CH₂)₁₇–CH₃) monolayers have been prepared on hydroxylated Si(100) surfaces as well as hydroxylated chromium film surfaces. Dense line patterns have been written by UHV‐STM in constant current mode for various tunneling parameters (gap voltage, tunneling current, scan speed, and orientation) and transferred into the underlying substrate by wet etch techniques. The etched structures have been analyzed by means of scanning electron microscopy (SEM) and atomic force microscopy (AFM). Best resolution has been achieved without etch transfer for a 20 nm × 20 nm square written in hexadecanethiol/Au(111) with an edge definition of about 5 nm. Etch transfer of the STM nanopatterns in Au films resulted in 55 nm dense line patterns (15 nm deep) mainly broadened by the isotropic etch characteristic, while 35 nm wide and 30 nm deep dense line patterns written in octadecyltrichlorosilane/Si(100) and anisotropically etched into Si(100) could be achieved.     

Layer‐by‐Layer Conjugated Extension of a Semiconducting Polymer for High‐Performance Organic Field‐Effect Transistor

A donor–acceptor (D–A) semiconducting copolymer, PDPP‐TVT‐29, comprising a diketopyrrolopyrrole (DPP) derivative with long, linear, space‐separated alkyl side‐chains and thiophene vinylene thiophene (TVT) for organic field‐effect transistors (OFETs) can form highly π‐conjugated structures with an edge‐on molecular orientation in an as‐spun film. In particular, the layer‐like conjugated film morphologies can be developed via short‐term thermal annealing above 150 °C for 10 min. The strong intermolecular interaction, originating from the fused DPP and D–A interaction, leads to the spontaneous self‐assembly of polymer chains within close proximity (with π‐overlap distance of 3.55 Å) and forms unexpectedly long‐range π‐conjugation, which is favorable for both intra‐ and intermolecular charge transport. Unlike intergranular nanorods in the as‐spun film, well‐conjugated layers in the 200 °C‐annealed film can yield more efficient charge‐transport pathways. The granular morphology of the as‐spun PDPP‐TVT‐29 film produces a field‐effect mobility (μ _FET) of 1.39 cm² V^?1 s^?1 in an OFET based on a polymer‐treated SiO₂ dielectric, while the 27‐Å‐step layered morphology in the 200 °C‐annealed films shows high μ _FET values of up to 3.7 cm² V^?1 s^?1.     

Solution‐Processable Dithienothiophenoquinoid (DTTQ) Structures for Ambient‐Stable n‐Channel Organic Field Effect Transistors

A series of dialkylated dithienothiophenoquinoids ( DTTQ s), end‐functionalized with dicyanomethylene units and substituted with different alkyl chains, are synthesized and characterized. Facile one‐pot synthesis of the dialkylated DTT core is achieved, which enables the efficient realization of DTTQ s as n‐type active semiconductors for solution‐processable organic field effect transistors (OFETs). The molecular structure of hexyl substituted DTTQ‐6 is determined via single‐crystal X‐ray diffraction, revealing DTTQ is a very planar core. The DTTQ cores form a “zig‐zag” linking layer and the layers stack in a “face‐to‐face” arrangement. The very planar core structure, short core stacking distance (3.30 Å), short intermolecular S? N distance (2.84 Å), and very low lying lowest unoccupied molecular orbital energy level of ?4.2 eV suggest that DTTQ s should be excellent electron transport candidates. The physical and electrochemical properties as well as OFETs performance and thin film morphologies of these new DTTQ s are systematically studied. Using a solution‐shearing method, DTTQ‐11 exhibits n‐channel transport with the highest mobility of up to 0.45 cm² V^?1 s^?1 and a current ON/OFF ratio (I _ON/I _OFF) greater than 10⁵. As such, DTTQ‐11 has the highest electron mobility of any DTT‐based small molecule semiconductors yet discovered combined with excellent ambient stability. Within this family, carrier mobility magnitudes are correlated with the alkyl chain length of the side chain substituents of DTTQ s.     

Thermo‐Switchable Charge Transport and Electrocatalysis Using Metal‐Ion‐Modified pNIPAM‐Functionalized Electrodes

Metal ions (Ag⁺, Cu²⁺, Hg²⁺) are incorporated into an electropolymerized, poly(N‐isopropyl acrylamide), pNIPAM, thermosensitive polymer associated with an electrode using the “breathing‐in” method. The ion‐functionalized pNIPAM matrices reveal ion‐dependent gel‐to‐solid phase‐transition temperatures (28 ± 1 °C, 25 ± 1 °C, 40 ± 1 °C for the Ag⁺, Cu²⁺, and Hg²⁺‐modified pNIPAM, respectively). Furthermore, the ion‐functionalized polymers exhibit quasi‐reversible redox properties, and the ions are reduced to the respective Ag⁰, Cu⁰, and Hg⁰ nanocluster‐modified polymers. The metal‐nanocluster‐functionalized pNIPAM matrices enhance the electron transfer (they exhibit lower electron‐transfer resistances) in the compacted states. The electron‐transfer resistances of the metal‐nanocluster‐modified pNIPAM can be cycled between low and high values by temperature‐induced switching of the polymer between its contracted solid and expanded gel states, respectively. The enhanced electron‐transfer properties of the metal nanocluster‐functionalized polymer are attributed to the contacting of the metal nanoclusters in the contracted state of the polymers. This temperature‐switchable electron transfer across a Ag⁰‐modified pNIPAM was implemented to design a thermo‐switchable electrocatalytic process (the temperature‐switchable electrocatalyzed reduction of H₂O₂ by Ag⁰‐pNIPAM).     

Synthesis of Leaf‐Vein‐Like g‐C3N4 with Tunable Band Structures and Charge Transfer Properties for Selective Photocatalytic H2O2 Evolution

Photocatalytic H₂O₂ evolution through two‐electron oxygen reduction has attracted wide attention as an environmentally friendly strategy compared with the traditional anthraquinone or electrocatalytic method. Herein, a biomimetic leaf‐vein‐like g‐C₃N₄ as an efficient photocatalyst for H₂O₂ evolution is reported, which owns tenable band structure, optimized charge transfer, and selective two‐electron O₂ reduction. The mechanism for the regulation of band structure and charge transfer is well studied by combining experiments and theoretical calculations. The H₂O₂ yield of CN4 (287 µmol h^?1) is about 3.3 times higher than that of pristine CN (87 µmol h^?1), and the apparent quantum yield for H₂O₂ evolution over CN4 reaches 27.8% at 420 nm, which is much higher than that for many other current photocatalysts. This work not only provides a novel strategy for the design of photocatalyst with excellent H₂O₂ evolution efficiency, but also promotes deep understanding for the role of defect and doping sites on photocatalytic activity.     

Solution Processable Fluorenyl Hexa‐peri‐hexabenzocoronenes in Organic Field‐Effect Transistors and Solar Cells

The organization of organic semiconductor molecules in the active layer of organic electronic devices has important consequences to overall device performance. This is due to the fact that molecular organization directly affects charge carrier mobility of the material. Organic field‐effect transistor (OFET) performance is driven by high charge carrier mobility while bulk heterojunction (BHJ) solar cells require balanced hole and electron transport. By investigating the properties and device performance of three structural variations of the fluorenyl hexa‐peri‐hexabenzocoronene (FHBC) material, the importance of molecular organization to device performance was highlighted. It is clear from ¹H NMR and 2D wide‐angle X‐ray scattering (2D WAXS) experiments that the sterically demanding 9,9‐dioctylfluorene groups are preventing π–π intermolecular contact in the hexakis‐substituted FHBC 4 . For bis‐substituted FHBC compounds 5 and 6 , π–π intermolecular contact was observed in solution and hexagonal columnar ordering was observed in solid state. Furthermore, in atomic force microscopy (AFM) experiments, nanoscale phase separation was observed in thin films of FHBC and [6,6]‐phenyl‐C61‐butyric acid methyl ester (PC₆₁BM) blends. The differences in molecular and bulk structural features were found to correlate with OFET and BHJ solar cell performance. Poor OFET and BHJ solar cells devices were obtained for FHBC compound 4 while compounds 5 and 6 gave excellent devices. In particular, the field‐effect mobility of FHBC 6 , deposited by spin‐casting, reached 2.8 × 10^?3 cm² V^?1 s and a power conversion efficiency of 1.5% was recorded for the BHJ solar cell containing FHBC 6 and PC₆₁BM.     

Electric‐Field‐Assisted Nanostructuring of a Mott Insulator

Here, the first experimental evidence for a strong electromechanical coupling in the Mott insulator GaTa₄Se₈ that allows highly reproducible nanoscaled writing by means of scanning tunneling microscopy (STM) is reported. The local electric field across the STM junction is observed to have a threshold value above which the clean (100) surface of GaTa₄Se₈ becomes mechanically instable: at voltage biases >1.1 V, the surface suddenly inflates and comes in contact with the STM tip, resulting in nanometer‐sized craters. The formed pattern can be indestructibly “read” by STM at a lower voltage bias, thus allowing 5 Tdots inch^?2 dense writing/reading at room temperature. The discovery of the electromechanical coupling in GaTa₄Se₈ might give new clues in the understanding of the electric pulse induced resistive switching recently observed in this stoichiometric Mott insulator.     

Influence of Thiol Self‐Assembled Monolayer Processing on Bottom‐Contact Thin‐Film Transistors Based on n‐Type Organic Semiconductors

The performance of bottom‐contact thin‐film transistor (TFT) structures lags behind that of top‐contact structures owing to the far greater contact resistance. The major sources of the contact resistance in bottom‐contact TFTs are believed to reflect a combination of non‐optimal semiconductor growth morphology on the metallic contact surface and the limited available charge injection area versus top‐contact geometries. As a part of an effort to understand the sources of high charge injection barriers in n‐channel TFTs, the influence of thiol metal contact treatment on the molecular‐level structures of such interfaces is investigated using hexamethyldisilazane (HMDS)‐treated SiO₂ gate dielectrics. The focus is on the self‐assembled monolayer (SAM) contact surface treatment methods for bottom‐contact TFTs based on two archetypical n‐type semiconductors, α,ω‐diperfluorohexylquarterthiophene (DFH‐4T) and N,N′bis(n‐octyl)‐dicyanoperylene‐3,4:9,10‐bis(dicarboximide) (PDI‐8CN₂). TFT performance can be greatly enhanced, to the level of the top contact device performance in terms of mobility, on/off ratio, and contact resistance. To analyze the molecular‐level film structural changes arising from the contact surface treatment, surface morphologies are characterized by atomic force microscopy (AFM) and scanning tunneling microscopy (STM). The high‐resolution STM images show that the growth orientation of the semiconductor molecules at the gold/SAM/semiconductor interface preserves the molecular long axis orientation along the substrate normal. As a result, the film microstructure is well‐organized for charge transport in the interfacial region.     

Photoinduced Magnetization with a High Curie Temperature and a Large Coercive Field in a Co‐W Bimetallic Assembly

The crystal structure, magnetic properties, and temperature‐ and photoinduced phase transition of [{Co^II(4‐methylpyridine)(pyrimidine)}₂{Co^II(H₂O)₂}{W^V(CN)₈}₂]·4H₂O are described. In this compound, a temperature‐induced phase transition from the Co^II (S = 3/2)‐NC‐W^V(S = 1/2) [high‐temperature (HT)] phase to the Co^III(S = 0)‐NC‐W^IV(S = 0) [low temperature (LT)] phase is observed due to a charge‐transfer‐induced spin transition. When the LT phase is irradiated with 785 nm light, ferromagnetism with a high Curie temperature (T_C) of 48 K and a gigantic magnetic coercive field (H_c) of 27 000 Oe are observed. These T_C and H_c values are the highest in photoinduced magnetization systems. The LT phase is optically converted to the photoinduced phase, which has a similar valence state as the HT phase due to the optically induced charge‐transfer‐induced spin transition.     

Structure and Morphology of PDI8‐CN2 for n‐Type Thin‐Film Transistors

A multiscale investigation of N,N′‐bis(n‐octyl)‐x:y, dicyanoperylene‐3,4:9,10‐bis(dicarboximide), PDI8‐CN2, shows the same molecular arrangement in the bulk and in thin films sublimated on SiO₂/Si wafers. Non‐conventional powder diffraction methods and theoretical calculations concur to provide a coherent picture of the crystalline structure. X‐ray diffraction (XRD) and atomic force microscopy (AFM) analyses of films of different thickness deposited at different substrate temperatures indicate the existence of two temperature‐dependent deposition regimes: a low‐temperature (room temperature) regime and a high‐temperature (80–120 °C) one, each characterized by different growth mechanisms. These mechanisms eventually result in different morphological and structural features of the films, which appear to be highly correlated with the trend of the electrical parameters that are measured in PDI8‐CN2‐based field‐effect transistors.     

Field‐Induced n‐Doping of Black Phosphorus for CMOS Compatible 2D Logic Electronics with High Electron Mobility

Black phosphorus (BP) has been considered as a promising two‐dimensional (2D) semiconductor beyond graphene owning to its tunable direct bandgap and high carrier mobility. However, the hole‐transport‐dominated characteristic limits the application of BP in versatile electronics. Here, we report a stable and complementary metal oxide semiconductor (COMS) compatible electron doping method for BP, which is realized with the strong field‐induced effect from the K⁺ center of the silicon nitride (Si_xN_y). An obvious change from pristine p‐type BP to n type is observed after the deposit of the Si_xN_y on the BP surface. This electron doping can be kept stable for over 1 month and capable of improving the electron mobility of BP towards as high as ~176 cm² V^–1 s^–1. Moreover, high‐performance in‐plane BP p‐n diode and further logic inverter were realized by utilizing the n‐doping approach. The BP p‐n diode exhibits a high rectifying ratio of ~10⁴. And, a successful transfer of the output voltage from “High” to “Low” with very few voltage loss at various working frequencies were also demonstrated with the constructed BP inverter. Our findings paves the way for the success of COMS compatible technique for BP‐based nanoelectronics.     

Catalytic materials manufactured by the polyol process for monolithic dye‐sensitized solar cells

Three types of screen‐printable catalytic pastes were successfully prepared to be used as counterelectrode for monolithic dye solar cells encapsulated with glass frit. The electroless bottom‐up method or so‐called polyol process has been applied to fabricate thermally stable SnO₂:Sb/Pt and carbon black/Pt nanocomposites. The catalytic and electric properties of these materials were compared with a new platinum‐free type of carbon counterelectrode. The layers containing low platinum amounts (less than 5 µg/cm²) exhibit a very low charge transfer resistance of about 0·4 Ω · cm². Also the conductive carbon layer shows an acceptable charge transfer resistance of 1·6 Ω · cm². Additionally the catalytic layer containing porous carbon black reveals excellent sheet resistance below 5 Ω/□; this feature has enabled to work out a low cost counterelectrode which combined suitable catalytic and conductive properties. The layers have been characterized using following methods: electrochemical impedance spectroscopy (EIS), field emission scanning electron microscopy (FE‐SEM), energy filter transmission electron microscopy (EF‐TEM) and inductively coupled plasma mass spectroscopy (ICP‐MS). Copyright © 2008 John Wiley & Sons, Ltd.     

Cyano‐Substituted Oligo(p‐phenylene vinylene) Single Crystals: A Promising Laser Material

Organic crystals that combine high charge‐carrier mobility and excellent light‐emission characteristics are expected to be of interest for light‐emitting transistors and diodes, and may offer renewed hope for electrically pumped laser action. High‐luminescence‐efficiency cyano‐substituted oligo(p‐ phenylene vinylene) (CN‐DPDSB) crystals (η ≈ 95%) grown by the physical vapor transport method is reported here, with high mobilities (at ≈10^?2 cm² V^?1 s^?1 order of magnitude) as measured by time‐of‐flight. The CN‐DPDSB crystals have well‐balanced bipolar carrier‐transport characteristics (μ_hole≈ 2.5–5.5 × 10^?2 cm² V^?1 s^?1; μ_electron ≈ 0.9–1.3 × 10^?2 cm² V^?1 s^?1) and excellent optically pumped laser properties. The threshold for amplified spontaneous emission (ASE) is about 4.6 μJ per pulse (23 KW cm^?2), while the gain coefficient at the peak wavelength of ASE and the loss coefficient caused by scattering are ≈35 and ≈1.7 cm^?1, respectively. This indicates that CN‐DPDSB crystals are promising candidates for organic laser diodes.     

UV‐vis‐Induced Vitrification of a Molecular Crystal

A charge‐transfer complex of 2,5‐dimethyl‐N,N′‐dicyanoquinonediimine (DM) with silver (crystalline Ag(DM)₂, defined as α) is irreversibly transformed by UV‐vis illumination. Depending on the illumination conditions, three new types of solids (defined as γ, δ, and ?) with different structural and physical properties are obtained and examined by a variety of analytical techniques, including solid‐state, high‐resolution, cross‐polarization magic angle spinning (CP‐MAS) ¹³C NMR, elemental analysis (EA), mass spectrometry (MS), X‐ray absorption fine structure (XAFS), and powder X‐ray diffraction (XRD). The CP‐MAS, EA, MS, and XAFS results indicate that compound γ is a glass state of Ag(DM)₂. The transformation from crystalline (α) to amorphous (γ) solid Ag(DM)₂ is an irreversible exothermic glass transition (glass‐transition temperature 155.2 °C; ΔH = –126.8 kJ mol^–1), which implies that the glass form is thermodynamically more stable than the crystalline form. Compound δ (Ag(DM)_1.5) consists of silver nanoparticles (diameter (7 ± 2) nm ) dispersed in a glassy matrix of neutral DM molecules. The ?N–CN–Ag coordination bonds of the α form are not maintained in the δ form. Decomposition of α by intense illumination results in a white solid (?), identified as being composed of silver nanoparticles (diameter (60 ± 10) nm). Physical and spectroscopic (XAFS) measurements, together with XRD analysis, indicate that the silver nanoparticles in both δ and ? are crystalline with lattice parameters similar to bulk silver; however, the magnetic susceptibilities differ from bulk silver.     

Alkoxy‐Functionalized Thienyl‐Vinylene Polymers for Field‐Effect Transistors and All‐Polymer Solar Cells

π‐conjugated polymers based on the electron‐neutral alkoxy‐functionalized thienyl‐vinylene (TVTOEt) building‐block co‐polymerized, with either BDT (benzodithiophene) or T2 (dithiophene) donor blocks, or NDI (naphthalenediimide) as an acceptor block, are synthesized and characterized. The effect of BDT and NDI substituents (alkyl vs alkoxy or linear vs branched) on the polymer performance in organic thin film transistors (OTFTs) and all‐polymer organic photovoltaic (OPV) cells is reported. Co‐monomer selection and backbone functionalization substantially modifies the polymer MO energies, thin film morphology, and charge transport properties, as indicated by electrochemistry, optical spectroscopy, X‐ray diffraction, AFM, DFT calculations, and TFT response. When polymer P7 is used as an OPV acceptor with PTB7 as a donor, the corresponding blend yields TFTs with ambipolar mobilities of μ_e = 5.1 × 10^?3 cm² V^–1 s^–1 and μ_h = 3.9 × 10^?3 cm² V^–1 s^–1 in ambient, among the highest mobilities reported to date for all‐polymer bulk heterojunction TFTs, and all‐polymer solar cells with a power conversion efficiency (PCE) of 1.70%, the highest reported PCE to date for an NDI‐polymer acceptor system. The stable transport characteristics in ambient and promising solar cell performance make NDI‐type materials promising acceptors for all‐polymer solar cell applications.     

Effect of Molecular Weight on the Structure and Morphology of Oriented Thin Films of Regioregular Poly(3‐hexylthiophene) Grown by Directional Epitaxial Solidification

Regioregular head‐to‐tail (HT)‐coupled poly(3‐hexylthiophene‐2,5‐diyl) (P3HT) with a weight‐average molecular weight (M_w) in the 7.3–69.6 kDa range is crystallized by directional epitaxial solidification in 1,3,5‐trichlorobenzene (TCB) to yield highly oriented thin films. An oriented and periodic lamellar structure consisting of crystalline lamellae separated by amorphous interlamellar zones is evidenced by atomic force microscopy (AFM) and transmission electron microscopy (TEM). Both the overall crystallinity as well as the orientation of the crystalline lamellae decrease significantly with increasing M_w. The total lamellar periodicity is close to the length of “fully extended” chains for M_w = 7.3 kDa (polystyrene‐equivalent molecular weight, eq. PS) and it saturates to a value of ca. (25–28) ± 2 nm for M_w ≥ 18.8 kDa (eq. PS). This behavior is attributed to a transition from an oligomeric‐like system, for which P3HT chains are essentially in a fully extended all‐trans conformation and do not fold, to a semicrystalline system that involves a periodic alternation of crystalline lamellae separated by extended amorphous interlamellar zones, which harbor chain folds, chain ends, and tie molecules. For P3HT with M_w of ca. 7.3 kDa (eq. PS), epitaxial crystallization on TCB allows for the growth of both “edge‐on” and “flat‐on” oriented crystalline lamellae on the TCB substrate. The orientation of the lamellae is attributed to 1D epitaxy. Because of the large size of the “flat‐on” crystalline lamellae, a characteristic single‐crystal electron diffraction pattern corresponding to the [001] zone was obtained by selected area electron diffraction (SAED), indicating that P3HT crystallizes in a monoclinic unit cell with a = 16.0 Å, b = 7.8 Å, c = 7.8 Å, and γ = 93.5°.     

Bithienopyrroledione‐Based Copolymers,Versatile Semiconductors for Balanced Ambipolar Thin‐Film Transistors and Organic Solar Cells with V oc > 1 V

Conjugated polymer semiconductors P1 and P2 with bithienopyrroledione (bi‐TPD) as acceptor unit are synthesized. Their transistor and photovoltaic performances are investigated. Both polymers display high and balanced ambipolar transport behaviors in thin‐film transistors. P1‐ based devices show an electron mobility of 1.02 cm² V^?1 s^?1 and a hole mobility of 0.33 cm² V^?1 s^?1, one of the highest performance reported for ambipolar polymer transistors. The electron and hole mobilities of P2 transistors are 0.36 and 0.16 cm² V^?1 s^?1, respectively. The solar cells with PC₇₁BM as the electron acceptor and P1/P2 as the donor exhibit a high V _oc about 1.0 V, and a power conversion efficiency of 6.46% is observed for P1‐ based devices without any additives and/or post treatment. The high performance of P1 and P2 is attributed to their crystalline films and short π–π stacking distance (<3.5 Å). These results demonstrate (1) bi‐TPD is an excellent versatile electron‐deficient unit for polymer semiconductors and (2) bi‐TPD‐based polymer semiconductors have potential applications in organic transistors and organic solar cells.     

Interlayer Band‐to‐Band Tunneling and Negative Differential Resistance in van der Waals BP/InSe Field‐Effect Transistors

Atomically thin layers of van der Waals (vdW) crystals offer an ideal material platform to realize tunnel field‐effect transistors (TFETs) that exploit the tunneling of charge carriers across the forbidden gap of a vdW heterojunction. This type of device requires a precise energy band alignment of the different layers of the junction to optimize the tunnel current. Among 2D vdW materials, black phosphorus (BP) and indium selenide (InSe) have a Brillouin zone‐centered conduction and valence bands, and a type II band offset, both ideally suited for band‐to‐band tunneling. TFETs based on BP/InSe heterojunctions with diverse electrical transport characteristics are demonstrated: forward rectifying, Zener tunneling, and backward rectifying characteristics are realized in BP/InSe junctions with different thickness of the BP layer or by electrostatic gating of the junction. Electrostatic gating yields a large on/off current ratio of up to 10⁸ and negative differential resistance at low applied voltages (V ≈ 0.2 V). These findings illustrate versatile functionalities of TFETs based on BP and InSe, offering opportunities for applications of these 2D materials beyond the device architectures reported in the current literature.     

Reactive Imprint Lithography: Combined Topographical Patterning and Chemical Surface Functionalization of Polystyrene‐block‐poly(tert‐butyl acrylate) Films

Here, reactive imprint lithography (RIL) is introduced as a new, one‐step lithographic tool for the fabrication of large‐area topographically patterned, chemically activated polymer platforms. Films of polystyrene‐block‐poly(tert‐butyl acrylate) (PS‐b‐PtBA) are imprinted with PDMS master stamps at temperatures above the corresponding glass transition and chemical deprotection temperatures to yield structured films with exposed carboxylic acid and anhydride groups. Faithful pattern transfer is confirmed by AFM analyses. Transmission‐mode FTIR spectra shows a conversion of over 95% of the tert‐butyl ester groups after RIL at 230 °C for 5 minutes and a significantly reduced conversion to anhydride compared to thermolysis of neat films with free surfaces in air or nitrogen. An enrichment of the surface layer in PS is detected by angle‐resolved X‐ray photoelectron spectroscopy (XPS). In order to demonstrate application potentials of the activated platforms, a 7 nm ± 1 nm thick NH₂‐terminated PEG layer (grafting density of 0.9 chains nm^?2) is covalently grafted to RIL‐activated substrates. This layer reduces the non‐specific adsorption (NSA) of bovine serum albumin by 95% to a residual mass coverage of 9.1 ± 2.9 ng cm^?2. As shown by these examples, RIL comprises an attractive complementary approach to produce bio‐reactive polymer surfaces with topographic patterns in a one‐step process.     

Diketopyrrolopyrrole‐Based Conjugated Polymers Synthesized via Direct Arylation Polycondensation for High Mobility Pure n‐Channel Organic Field‐Effect Transistors

High‐performance unipolar n‐type conjugated polymers (CPs) are critical for the development of organic electronics. In the current paper, four “weak donor–strong acceptor” n‐type CPs based on pyridine flanked diketopyrrolopyrrole (PyDPP), namely PPyDPP1‐4FBT, PPyDPP2‐4FBT, PPyDPP1‐4FTVT, and PPyDPP2‐4FTVT, are synthesized via direct arylation polycondensation by using 3,3′,4,4′‐tetrafluoro‐2,2′‐bithiophene (4FBT) or (E)‐1,2‐bis(3,4‐difluorothien‐2‐yl)ethene (4FTVT) as weak donor unit. All four polymers exhibit low‐lying highest occupied molecular orbital (≈ ?5.90 eV) and lowest unoccupied molecular orbital energy levels (≈ ?3.70 eV). Top‐gate/bottom‐contact organic field‐effect transistors based on all four polymers display unipolar n‐channel characteristics with electron mobility (µ_e) above 1 cm² V^?1 s^?1 in air, and presented linear |I_SD|^1/2 ?V_GS plots and weak dependence of the extracted moblity on gate voltage (V_GS), indicative of the reliability of the extracted mobility values. Importantly, the devices based on PPyDPP1‐4FBT and PPyDPP2‐4FBT show a pure unipolar n‐channel transistor behavior as revealed by the typical unipolar n‐channel output characteristics and clear off‐regimes in transfer characteristics. Attributed to its high crystallinity and favorable thin film morphology, PPyDPP2‐4FBT shows the highest µ_e of 2.45 cm² V^?1 s^?1, which is among the highest for unipolar n‐type CPs reported to date. This is also the first report for DPP based pure n‐type CPs with µ_e greater than 1 cm² V^?1 s^?1.