Thursday, February 25, 2010

3M Discloses Solar Cells, Transistors and LEDs Containing Acene-Thiophene Copolymers and Nanoparticles

3M Innovative Properties Company (St. Paul, MN) earned U.S. Patent 7,667,230 for electronic devices that contain an acene-thiophene copolymer. The acene-thiophene copolymer can be present in a layer that is adjacent to a dielectric layer, a conductive layer, or combinations of them. More specifically, the acene-thiophene copolymer can function as a semiconducting material in electronic devices such as an organic thin film transistor or can be positioned between two electrodes in electronic devices such as an organic photovoltaic cell or an organic luminescent device, according to inventors Peiwang Zhu, Tzu-Chen Lee, Dennis E. Vogel and Christopher P. Gerlach

Traditionally, inorganic materials have dominated the electronic device industry. For example, silicon arsenide and gallium arsenide have been used as semiconductor materials, silicon dioxide has been used as an insulator material, and metals such as aluminum and copper have been used as electrode materials. In recent years, however, there has been an increasing research effort aimed at using organic materials rather than the traditional inorganic materials in electronic devices. Among other benefits, the use of organic materials may enable lower cost manufacturing of electronic devices, may enable large area applications, and may enable the use of flexible circuit supports for display backplane and integrated circuits.

A variety of organic semiconductor materials have been considered, the most common being fused aromatic ring compounds as exemplified by small molecules such as pentacene-containing compounds, tetracene-containing compounds, anthracene-containing compounds, bis(acenyl)acetylene compounds, and acene-thiophene compounds. Several polymeric materials have also been considered such as regioregular polythiophenes such as poly(3-alkylthiophene) and polymers having fused thiophene units or bis-thiophene units. However, at least some of the polymers tend to undergo oxidation, which can lead to diminished electronic device performance. 
               
3M’s electronic devices and methods of making electronic devices that include an acene-thiophene copolymer are thin film photovoltaic cells, organic thin film transistors and organic light emitting diodes. . The gate electrode in some embodiments is formed by coating a substrate surface with a dispersion that contains conductive materials such as nanoparticles that are conductive or polymeric materials that are conductive. Conductive nanoparticles include ITO nanoparticles, ATO nanoparticles, silver nanoparticles, gold nanoparticles, or carbon nanotubes or others

Organic photovoltaic cells and organic luminescent devices include many common components such as an anode, a cathode, and a material positioned between the anode and cathode. However, the operation principals of these two types of devices are reversed. In an organic luminescent device, light is emitted as the result of charge transport between the two electrodes. An electron is introduced at a first electrode having a low work function (i.e., the cathode) and a hole is introduced at a second electrode having a high work function (i.e., the anode). In the organic emissive element positioned between the two electrodes, the electron and hole recombine and emit light.

Conversely, in a photovoltaic cell, charge transport between the two electrodes results from the exposure of the active layer to light. The active layer, which is positioned between two electrodes, adsorbs light that passes through one of the electrodes. The absorption of light causes the formation of an exiton (i.e., an excited electron-hole pair) that is subsequently dissociated into an electron and a hole that migrate towards opposite electrodes.

Organic electroluminescent (OEL) devices such as organic light emitting diodes include an organic emissive element positioned between two electrodes (i.e., an anode and a cathode). The organic emissive element of an organic electroluminescent device usually includes at least one light emitting layer that include an electroluminescent material. Other layers can also be present in the organic emissive element such as hole transport layers, electron transport layers, hole injection layers, electron injection layers, hole blocking layers, electron blocking layers, buffer layers, and the like.

In addition, photoluminescent materials can be present in the light emitting layer or other layers in the organic emissive element, for example, to convert the color of light emitted by the electroluminescent material to another color. These and other such layers and materials can be used to alter or tune the electronic properties and behavior of the layered OEL device. For example, the additional layers can be used to achieve a desired current/voltage response, a desired device efficiency, a desired color, a desired brightness, and the like

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