Wenchong Wang

Controllable Growth and Field-Effect Property of Monolayer to Multilayer Microstripes of an Organic Semiconductor

The controllable growth of partially aligned monolayer to multilayer micrometer stripes was demonstrated by adjusting the pulling speed in a dip-coating process. The number of molecular layers decreases with the increasing pulling speed. A lower pulling speed yields mixed multilayers (3-9 monolayers). It is noteworthy that pure monolayer and bilayer microstripes over large areas can be obtained at high pulling speeds. The stripe morphology strongly depends on the pulling speed or the number of molecular layers. XRD and confocal fluorescence measurements manifest that monolayer stripes are amorphous, while multilayer stripes (> or = 2) consist of crystalline states. FET devices were fabricated on these stripes. Monolayer stripes failed to reveal a field effect due to their amorphous state. In contrast, multilayer stripes exhibit good field-effect behavior. This study provides useful information for future molecular design in controlling molecular architectures. The controllable growth from monolayer to multilayer offers a powerful experimental system for fundamental research into the real charge accumulation and transporting layers for OFETs.

Patterning of polymer electrodes by nanoscratching.

2010 WILEY-VCH Verlag Gmb Growing scientific effort is being devoted to building electronic circuits entirely or partially of organic materials because of their attractive characteristics such as low cost, light weight, and mechanical flexibility. To realize low-cost and high-performance organic transistor circuits for practical applications, utilization of low-cost electrodes (such as conducting polymers) and downscaling the transistor critical feature to the sub-micro/ nanometer scale are two necessary concepts. However, integration of these two strategies, i.e., patterning polymer electrodes with sub-micro/nanometer resolution, remains a great challenge. Here we demonstrate the patterning of the conducting polymer poly(3,4-ethylenedioxythiophene):poly(4-styrenesulphonate) (PEDOT:PSS) (Fig. 1a), an excellent organic electrode material, with 50 nm resolution on both rigid and flexible substrates by atomic force microscopy (AFM) nanoscratching. The scratched grooves show good stability under solvent immersion, heat treatment, and long-term storage in air. This technique can realize small organic transistor electrode pairs (area of 0.5–0.6mm) and a high density electrode array (about 10 elements cm ). The small linewidth of the patterned PEDOT:PSS electrodes yields a parasitic overlap capacitance as low as 0.09 pF mm . The scratched sub-micro/nanometer channel shows excellent performance in organic transistors with high performance and low voltage. Downscaling the size of a single transistor not only allows the realization of high integration density and miniaturization of circuits, but also facilitates improved circuit performance and/or switching speed, as well as lower power consumption. Up to now, organic transistor-based circuits with a relatively fast switching speed (1 KHz to 20MHz) and large integration density ( 2000 transistors) have been demonstrated with metal electrodes defined by high resolution but complicated and expensive photolithography or e-beam lithography. It is widely recognized that the high cost of gold electrodes will overshadow the practical application of organic circuits, while polymer electrodes have a unique ability to fully embody the advantages of organic circuits such as low cost and mechanical flexibility, as well as the ability to achieve higher circuit performance because of their excellent compatibility with organic semiconductors. However, organic transistors/circuits with polymer electrodes such as PEDOT:PSS generally fabricated by volume printing techniques yield a much lower speed of 1–100Hz and require a relatively high voltage of 20–100V, mainly because of the poor resolution (10–50mm) of the direct-printing technique. In addition to mobility, the switching speed of a transistor is inversely proportional to channel length and the overlap linewidth between gate and source/drain electrodes (see Equation (3) in the Experimental section). Therefore, in order to achieve high-performance organic circuits with polymer electrodes, an effective but certainly challenging route is to define polymer electrode materials with submicro/nanometer resolution through a simple and low cost procedure. AFM lithography is a cost-effective and reliable technique for pattering submicro/nanometer-scale structures without complicated steps in comparison with other patterning techniques. To date, there is no report on the use of AFM nanoscratching to structure conducting polymers such as PEDOT:PSS. Figure 1b–d illustrate the schematic process of nanoscratching with a silicon tapping-mode cantilever (Supporting Information 1) in contact mode on a PEDOT:PSS film. Figure 1e shows an exemplified groove formed by nanoscratching, and the groove width is about 50 nm, which is the narrowest PEDOT:PSS groove reported to date. Although a sub-micrometer PEDOT:PSS groove has been achieved for transistor applications by a modified-printing method, this technique requires a prepatterning process based on an original patterningmethod such as photolithography, which will definitely increase the complexity and cost of the manufacturing process. The surface plot (Fig. 2a) and section analysis (Fig. 2b) clearly show the geometry of the multiple grooves. Figure 2c displays the

High-performance and stable organic transistors and circuits with patterned polypyrrole electrodes.

High performance p-/n-type transistors and complementary inverter circuits are demonstrated using patterned polypyrrole (PPY) as pure electrodes. Strikingly, these devices show good stability under continuous operation and long-term storage conditions. Furthermore, PPY electrodes also exhibit good applicability in solution-processed and flexible devices. All these results indicate the great potential of PPY electrodes in solution-processed, all-organic, flexible, transparent, and low-power electronics.

Tunable Multicolor Ordered Patterns with Two Dye Molecules

Since their invention in 1987 by Tang et al, [ 1 ] small-molecule organic light-emitting diodes (OLEDs) have been the subject of intense scientifi c and technological investigation for applications ranging from lighting [ 2 ] and displays [ 3 ] to sensors. [ 4 ] Although monocolor OLEDs are suffi cient for some applications, color integration on a single substrate could greatly enhance their technological impact, especially for full-color displays. Mostly, the challenge lies in the production of user-defi ned multicolor patterns with suffi cient resolution, owing to the absence of patterning techniques such as photolithography as applied for inorganic semiconductors. Several techniques have been developed, such as subsequent deposition with shadow masks, [ 5 ] vapor jet printing, [ 6 ] reconfi guration of devices by thermal imaging, [ 7 ]

High‐Resolution Triple‐Color Patterns Based on the Liquid Behavior of Organic Molecules

Driven by anticipation of novel applications, enormous progress has been made in organic semiconductors since the 1950s. Historically, much of the initial work was centered on organic light-emitting diodes (OLEDs) [ 1 , 2 ] and photovoltaics (PVs) [ 3 , 4 ] due to their intensive applications. Owing to efforts from both academia and industry over the last two decades, the research interest has dramatically expanded to transistors, [ 5 ] sensors, [ 6 ] memories, [ 7 ] lasers, [ 8 ] etc. In organic microelectronics and optoelectronics, the ability to create scalable high-resolution patterns of semiconductor organic molecules still presents challenges for fabrication technology. As an example, a full-color microdisplay requires high-resolution red, green, and blue (RGB) OLEDs to be patterned in close proximity of micrometers. Current patterning techniques based on shadow-mask [ 9 ] and vapor-jet printing [ 10 ] suffer from low resolution, poor scalability, and complicated multistep processing. Previously, we demonstrated the template-directed growth technique as a promising method for patterning organic semiconductors with tunable physical properties. [ 11–13 ] Herein, we show the liquid behavior of appropriately selected dye molecules on prepatterned substrates. By further controlling the diffusion of molecules between designed patterns, we achieve heteropatterning of organic materials, that is, the thickness of organic molecule patterns differs in a controlled way over predefi ned areas. Further deposition of a second type of molecule on the heteropatterned structure produces high-resolution, ordered, triple-color organic patterns using only two dyes. In this study, we use N , N ′ -di[( N -(3,6-ditertbutylcarbazyl))n -decyl] quinacridone (DtCDQA), an orange light-emitting material with high quantum yield and multiple emission states in both liquid and solid solvents. [ 13 ]

The electrode's effect on the stability of organic transistors and circuits.

Dr. L. Li , Dr. L. Jiang , C. Du , Dr. W W. ang , Prof. H. uchs , F Prof. L. Chi Physikalisches Institut and Center for Nanotechnology (CeNTech)Universitat Munster Munster, 48149, Germany E-mail: chi@uni-muenster.de Dr. K. Meise-Gresch Physikalische Chemie Institut Universitat Munster Munster, 48149, Germany

Addressable Organic Structure by Anisotropic Wetting

The anisotropic wetting of functional organic molecules on a patterned surface and the development of a photolithography-compatible method to fabricate addressable organic structures is reported. For example, DtCDQA is grown on a SiO2 surface with a Au prepattern, achieving a high resolution cross-over organic structure.

Surface Microfluidic Patterning and Transporting Organic Small Molecules

Transregional Collaborative Research Centre TRR 61, DFG; NSFC; EU [FP7-People-2009-IRSES/247641]; China Scholarship Council

Different growth regimes on prepatterned surfaces: consistent evidence from simulations and experiments.

Molecule deposition on a prepatterned substrate is a recently developed technique to generate desired structures of organic molecules on surfaces via self-organization. For the case of prepatterned stripes, the time-resolved process of structure formation is studied via lattice Monte Carlo simulations. By systematic variation of the interaction strength, three distinct growth regimes can be identified: localized growth, bulge formation, and cluster formation. All three growth regimes can be recovered in the experiment when choosing appropriate organic molecules. Some key microscopic observables, reflecting the properties of the structure formation, display a non-monotonous dependence on the interaction strength.

Anisotropic growth of organic semiconductor based on mechanical contrast of pre-patterned monolayer

Site-selective anisotropic growth of perylene film is achieved by using a striped Langmuir–Blodgett (LB) monolayer as an alignment layer. The stripes significantly increase the grain size along the stripe direction due to increased diffusion length. By controlling the grain boundaries and the molecular alignment, a mobility anisotropic ratio of ∼10 for the current flow parallel and perpendicular to the stripes has been observed.