Flexible Bottom-Gated Organic Field-Effect Transistors Utilizing Stamped Polymer Layers from the Surface of Water.

The facile sequential deposition of functional organic thin films by solution processes is critical for the development of a variety of high-performance organic devices without restriction in terms of materials and processes. Herein, we propose a simple fabrication process that entails stacking multiple layers of functional polymers to fabricate organic field-effect transistors (OFETs). The process involves stamping organic semiconducting layers formed on the surface of water onto a commonly used polymeric dielectric layer.

Understanding the Performance of Organic Photovoltaics under Indoor and Outdoor Conditions: Effects of Chlorination of Donor Polymers.

Understanding the effects of the chemical structures of donor polymers on the photovoltaic properties of their corresponding organic photovoltaic (OPV) devices under various light-intensity conditions is important for improving the performance of these devices. We synthesized a series of copolymers based on poly[(2,6-(4,8-bis(5-(2-thioethylhexyl)thiophen-2-yl)benzo[1,2-:4,5-']dithiophene))--(5,5-(1',3'-di-2-thienyl-5',7'-bis(2-ethylhexyl)benzo[1',2'-:4',5'-']dithiophene-4,8-dione))] (PBDB-TS) and studied the effects of chlorine substitution of its thiophene-substituted benzodithiophene (BDT-Th) unit on its photovoltaic properties. Chlorination of the polymer resulted in a bulk heterojunction (BHJ) morphology optimized for efficient charge transport with suppressed leakage current and an increased open-circuit voltage of the OPV device; this optimization led to a remarkable enhancement of the OPV device's power conversion efficiency (PCE) not only under the condition of 1 sun illumination but also under a low light intensity mimicking indoor light; the PCE increased from 8.

Role of Schottky Barrier and Access Resistance in Organic Field-Effect Transistors.

Despite the increasing understanding of charge transport in organic field-effect transistors (OFETs), charge injection from source/drain electrodes into organic semiconductors remains crucial for improving device performance and lowering power consumption. The analysis of contact resistance is generally carried out without clearly distinguishing the Schottky barrier and access resistance. Here we show that the access resistance through the organic semiconductor bulk can significantly influence the Schottky barrier evaluation and affect the charge-transport exploration.

Effect of Backbone Sequence of a Naphthalene Diimide-Based Copolymer on Performance in n-Type Organic Thin-Film Transistors.

We report two newly synthesized naphthalene diimide (NDI)-based conjugated polymers, poly[()-2,7-bis(2-decyltetradecyl)benzo[][3,8]phenanthroline-1,3,6,8(2,7)-tetraone-vinylene-thiophene-vinylene] (PNDI-VTV) and poly[()-2,7-bis(2-decyltetradecyl)benzo[][3,8]phenanthroline-1,3,6,8(2,7)-tetraone-vinylene-selenophene-vinylene] (PNDI-VSV) with different donor units as electron-transporting organic semiconductors for organic field-effect transistors (OFETs). Furthermore, we study the effect of vinylene position on electron transport in the NDI polymers by using two similar polymers but with thiophene-vinylene-thiophene (PNDI-TVT) instead of vinylene-thiophene-vinylene or selenophene-vinylene-selenophene (PNDI-SVS) instead of vinylene-selenophene-vinylene. By incorporating vinylene between thiophene (or selenophene) units, the resulting NDI-based polymers PNDI-VTV and PNDI-VSV show larger backbone planarity than PNDI-TVT and PNDI-SVS.

Synthesis and Characterization of Diketopyrrolopyrrole-Based Conjugated Polymers with Bithiophene and Biselenophene for Organic Thin Film Transistors.

In this study, two new thieno[3,2-]thiophene-diketopyrrolopyrrole (DPP)-based polymers, poly{2,5-bis(2-dodecylhexadecyl)-3,6-bis(thieno[3,2-]thiophen-2-yl)pyrrolo[3,4-]pyrrole-1,4(2,5)-dione-alt-2, 2'-bithiophene} (PTTDPP-BT) and {2,5-bis(2-dodecylhexadecyl)-3,6-bis(thieno[3,2-]thiophen-2-yl) pyrrolo[3,4-]pyrrole-1,4(2,5)-dione--2,2'-selenophene} (PTTDPP-BSe), which contained bithiophene (BT) and biselenophene (BSe) units, respectively, were designed and synthesized. The introduction of BT and BSe units affected the optical, electrochemical, morphological, and charge transport properties of the polymers. Experimental results revealed that the frontier molecular orbital energy levels of PTTDPP-BT were slightly higher because of the relatively strong electron donating ability of the sulfur atom and the polymer also exhibited good solubility.

Planar-Processed Polymer Transistors.

Planar-processed polymer transistors are proposed where the effective charge injection and the split unipolar charge transport are all on the top surface of the polymer film, showing ideal device characteristics with unparalleled performance. This technique provides a great solution to the problem of fabrication limitations, the ambiguous operating principle, and the performance improvements in practical applications of conjugated-polymer transistors.

Control of Threshold Voltage for Top-Gated Ambipolar Field-Effect Transistor by Gate Buffer Layer.

The threshold voltage and onset voltage for p-channel and n-channel regimes of solution-processed ambipolar organic transistors with top-gate/bottom-contact (TG/BC) geometry were effectively tuned by gate buffer layers in between the gate electrode and the dielectric. The work function of a pristine Al gate electrode (-4.1 eV) was modified by cesium carbonate and vanadium oxide to -2.

Nanoparticle scattering layer for improving light extraction efficiency of organic light emitting diodes.

Nanoparticle scattering layer based on polymer-metal oxide composite is successfully introduced to enhance the light extraction efficiency of organic light emitting diodes (OLEDs). We find that the density and the distribution of nanoparticles is the key factor to maximize the light extraction efficiency of pristine OLEDs by out-coupling the unusable light with the scattering film. In our experiment, 71 wt% of Al(2)O(3) mixed with polymer matrix shows the increase of light extraction efficiency of 40%.