Transparent metal electrodes fabricated by nanoimprint lithography show high optical transmittance as well as good electrical conductivity. Organic solar cells prepared using these transparent metal electrodes demonstrate an equal performance to those prepared with conventional ITO electrodes.

Organic light-emitting diodes (OLEDs) are promising for full-color, full-motion, flat panel display applications [1][2][3] because they offer several advantageous features, for example, ease of fabrication, low costs, light weight, bright self-emission, a wide viewing angle, and the possibility of flexible displays. The basic OLED structure consists of a number of organic semiconductor layers sandwiched between a cathode and an anode. For efficient electron injection into the organic layers, low-work-function materials are required for the cathode. A very thin LiF layer with a thick Al capping is widely used for this purpose.[4] For the anode, indium tin oxide (ITO)is the predominant choice because it offers transparency in the visible range of the electromagnetic spectrum as well as electrical conductivity.[ [5][6][7] However, several aspects of ITO are far from optimal for high-performance OLEDs. It is known that the migration of indium and oxygen from ITO into organic semiconductors during OLED operation causes device degradation. [8,9] The electrical properties of ITO greatly depend on the film preparation. [10,11] The rough surface of the deposited ITO film and the work function of ITO, ca. 4.7 eV, limit the efficiency of the hole injection. [12] The typical sheet resistance of a 100 nm thick ITO layer, 20-80 X/&, is still high, which causes a voltage drop along the addressing line, thus limiting the operation of a large-area passive matrix OLED array. [13] Moreover, the cost of ITO has escalated in recent years because of the jump in price of the element indium. Several alternative materials, for example, TiN, [14] Al-doped ZnO, [15] and fluorine tin oxide, [16] have been investigated as anode materials instead of ITO; however, none are optimal as anode in OLEDs because they have either a lower work function or a lower conductivity than ITO. Other transparent conducting oxides, such as, and Zn-In-O (ZIO), that have a higher work function and a similar electrical conductivity when compared to ITO have also been examined as OLED anode materials.[17] However, they are potentially problematic because they also contain the element indium that i) may diffuse into the organic layer in the OLED; and ii) has a high price, making these electrodes expensive. Besides these materials several metals with a high work function, such as Au, [12] Ni, [18] and Pt, [19] have been investigated as anodes for OLEDs. In these cases the metal was used to modify the surface of the ITO electrode, or as an anode for top-emitting devices. A surface-modified thin Ag film [20,21] has been used as a semitransparent electrode instead of ITO, but its transparency was low. Recently, carbon nanotube films have been investigated as transparent, conductive electrodes, [22][23][24][25] but they have a high sheet resistance that may limit the device performance.In this Communication, we report semitransparent metal electrodes fabricated by nanoimprint lithography (NIL), and evaluate their potential as OLED anodes. NIL, an emerging lithographic te...

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We developed simple fabrication methods to effectively transfer the block copolymer nanopatterns to a substrate material. High aspect ratio, sub-20 nm nanopillar and nanohole structures are successfully fabricated in a SiO(2) layer in large area format, and the versatile utilities of these nanostructures as nanoimprint molds are studied. Nanoimprint lithography using these molds makes it possible to easily replicate densely packed block copolymer nanotemplate patterns on arbitrary substrates in a short processing time by using a large variety of polymer materials, including functional materials such as conjugated polymers. In addition, the PDMS soft stamps with both nanohole and nanopillar pattern polarities, which are useful tools for soft lithography and transparent template applications, are also successfully fabricated using the pillar- and hole-type SiO(2) molds. These soft stamps provide an effective way to fabricate controllable as well as reproducible plasmonic metal nanostructures with tunable surface plasmon resonances.

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