Michael C. Gwinner

Periodic Large‐Area Metallic Split‐Ring Resonator Metamaterial Fabrication Based on Shadow Nanosphere Lithography

Metamaterials have gained substantial attention because of their potential for negative permeability as well as negative refractive index in the optical frequency range[1,2]. Due to their unique electromagnetic properties, these nanostructures show promise for numerous applications such as perfect lenses and optical cloaking devices.

Highly Efficient Single-Layer Polymer Ambipolar Light-Emitting Field-Effect Transistors

Single-layer polymer light-emitting field-effect transistors (LEFETs) that yield EQEs of >8% and luminance efficiencies >28 cd A(-1) are demonstrated. These values are the highest reported for LEFETs and amongst the highest values for fluorescent OLEDs. Due to the electrostatics of the ambipolar LEFET channel, LEFETs provide an inherent advantage over OLEDs in terms of minimizing exciton-polaron quenching.

High-Performance Electron-Transporting Polymers Derived from a Heteroaryl Bis(trifluoroborate)

In this communication, we report that dipotassium aryl bis(trifluoroborate)s make stable and easy-to-purify yet reactive monomers under Suzuki polycondensation reactions. A bis(trifluoroborate) of 2-alkylbenzotriazole was prepared successfully and copolymerized with dibromobenzothiadiazole in the presence of a Pd catalyst and LiOH, yielding high molecular weight conjugated polymers. This polymer (P1) composed of all electron-accepting units shows excellent electron-transport properties (μ(e) = 0.02 cm(2) V(-1) s(-1)), which proves the value of the aryl bis(trifluoroborate) monomers and suggests that many other types of semiconducting polymers that could not be accessed previously can be synthesized using this approach.

Enhanced ambipolar charge injection with semiconducting polymer/carbon nanotube thin films for light-emitting transistors.

We investigate the influence of small amounts of semiconducting single-walled carbon nanotubes (SWNTs) dispersed in polyfluorenes such as poly(9,9-di-n-octylfluorene-alt-benzothiadiazole (F8BT) and poly(9,9-dioctylfluorene) (F8) on device characteristics of bottom contact/top gate ambipolar light-emitting field-effect transistors (LEFETs) based on these conjugated polymers. We find that the presence of SWNTs within the semiconducting layer at concentrations below the percolation limit significantly increases both hole and electron injection, even for a large band gap semiconductor like F8, without leading to significant luminescence quenching of the conjugated polymer. As a result of the reduced contact resistance and lower threshold voltages, larger ambipolar currents and thus brighter light emission are observed. We examine possible mechanisms of this effect such as energy level alignment, reduced bulk resistance above the contacts, and field-enhanced injection at the nanotube tips. The observed ambipolar injection improvement is applicable to most conjugated polymers in staggered transistor configurations or similar organic electronic devices where injection barriers are an issue.

Organic field-effect transistors and solar cells using novel high electron-affinity conjugated copolymers based on alkylbenzotriazole and benzothiadiazole

Two novel conjugated copolymers based on alkylbenzotriazole and benzothiadiazole with high electron affinities are investigated for applications in polymer field-effect transistors and solar cells. The electron withdrawing nature of these polymers allows for efficient electron injection and transport. We were able to realize ambipolar red light-emitting field-effect transistors with electron mobilities exceeding 0.01 cm2 V−1 s−1 using gold electrodes. All-polymer solar cells with open-circuit voltages larger than 1.2 V using the new polymers as electron acceptor are also demonstrated.

Periodic large-area metallic split-ring resonator metamaterial fabrication based on shadow nanosphere lithography

Metamaterials have gained substantial attention because of their potential for negative permeability as well as negative refractive index in the optical frequency range[1,2]. Due to their unique electromagnetic properties, these nanostructures show promise for numerous applications such as perfect lenses and optical cloaking devices.