Interdigitated Hierarchical Integration of an Efficient Lateral Perovskite Single-Crystal Solar Cell.

Single-crystal perovskite thin films were prepared by a scalable, one-step, geometrically confined lateral crystal growth (GC-LCG) method on a patterned rolling mold and used for a photovoltaic study. A record solar cell efficiency of 9.50 % under 0.1 sun with an electrode spacing of 1.5 µm is attained in lateral single-crystal perovskite materials. Moreover, successful integration for high-source-power-generation interdigitated electrode units patterned in series (1×4), parallel (4×1), and combination (4 series×4 parallel) configurations is devised and affords maximum efficiencies of 7.99, 8.19, and 7.96 %, respectively. Additionally, the cell performances under various illumination intensities (0.1, 0.2, 0.4, 0.6, 0.8, 1.0 sun) to mimic daily sunshine angles and an indoor environment at 1000 lux are elucidated for which short-circuit current (JSC ) values (19.60 mA cm-2 and η=7.43 %) under 1.0 sun and a significant efficiency of 8.13 % under indoor conditions are obtained. This work represents a significant step towards next-generation, efficient, lateral photovoltaics for possible module integration.

Wafer-scale single-crystal perovskite patterned thin films based on geometrically-confined lateral crystal growth.

We report a facile roll-printing method, geometrically confined lateral crystal growth, for the fabrication of large-scale, single-crystal CH3NH3PbI3 perovskite thin films. Geometrically confined lateral crystal growth is based on transfer of a perovskite ink solution via a patterned rolling mould to a heated substrate, where the solution crystallizes instantly with the immediate evaporation of the solvent. The striking feature of this method is that the instant crystallization of the feeding solution under geometrical confinement leads to the unidirectional lateral growth of single-crystal perovskites. Here, we fabricated single-crystal perovskites in the form of a patterned thin film (3 × 3 inch) with a high carrier mobility of 45.64 cm2 V-1 s-1. We also used these single-crystal perovskite thin films to construct solar cells with a lateral configuration. Their active-area power conversion efficiency shows a highest value of 4.83%, which exceeds the literature efficiency values of lateral perovskite solar cells.

Observation of Charge Separation and Space-Charge Region in Single-Crystal P3HT/C60 Heterojunction Nanowires.

We directly observed charge separation and a space-charge region in an organic single-crystal p-n heterojunction nanowire, by means of scanning photocurrent microscopy. The axial p-n heterojunction nanowire had a well-defined planar junction, consisted of P3HT (p-type) and C60 (n-type) single crystals and was fabricated by means of the recently developed inkjet-assisted nanotransfer printing technique. The depletion region formed at the p-n junction was directly observed by exploring the spatial distribution of photogenerated carriers along the heterojunction nanowire under various applied bias voltages. Our study provides a facile approach toward the precise characterization of charge transport in organic heterojunction systems as well as the design of efficient nanoscale organic optoelectronic devices.

Single-crystal poly(3,4-ethylenedioxythiophene) nanowires with ultrahigh conductivity.

We developed single-crystal poly(3,4-ethylenedioxythiopene) (PEDOT) nanowires with ultrahigh conductivity using liquid-bridge-mediated nanotransfer printing with vapor phase polymerization. The single-crystal PEDOT nanowires are formed from 3,4-ethylenedioxythiophene (EDOT) monomers that are self-assembled and crystallized during vapor phase polymerization process within nanoscale channels of a mold having FeCl3 catalysts. These PEDOT nanowires, aligned according to the pattern in the mold, are then directly transferred to specific positions on a substrate to generate a nanowire array by a direct printing process. The PEDOT nanowires have closely packed single-crystalline structures with orthorhombic lattice units. The conductivity of the single-crystal PEDOT nanowires is an average of 7619 S/cm with the highest up to 8797 S/cm which remarkably exceeds literature values of PEDOT nanostructures/thin films. Such distinct conductivity enhancement of single-crystal PEDOT nanowires can be attributed to improved carrier mobility in PEDOT nanowires. To demonstrate usefulness of single-crystal PEDOT nanowires, we fabricated an organic nanowire field-effect transistor array contacting the ultrahigh conductive PEDOT nanowires as metal electrodes.

Molecular layer deposition of organic-inorganic hybrid films using diethylzinc and trihydroxybenzene.

We fabricated organic-inorganic hybrid thin films by using molecular layer deposition with diethylzinc and benzenetriol at temperatures of 100-160 °C. In this MLD process, the surface reactions were found to be self-terminating and complementary enough to make a uniform, conformal, high-quality hybrid thin film. The prepared zinc oxide-crosslinked hydroxybenzene and zinc oxide nanolaminated films (ZnOHB/ZnO) exhibited good stability and field effect mobility (> 0.6 cm2/V · s). The MLD method is an ideal technique for fabrication of various organic-inorganic hybrid thin films.

One-step fabrication of poly(9,9-dioctylfluorene) nanowire arrays with pronounced ß-phase using liquid-bridge-mediated nanotransfer molding.

Poly(9,9-dioctylfluorene) nanowire arrays with pronounced ß-phase were prepared by a one-step fabrication method, liquid-bridge-mediated nanotransfer molding. Liquid-bridge-mediated nanotransfer molding is a new direct nano-patterning method based on the direct transfer of various materials from a mold to a substrate via liquid layer. We fabricated poly(9,9-dioctylfluorene) nanowire arrays (80 nm parallel lines and 120 nm spaces) by Liquid-bridge-mediated nanotransfer molding using the poly(9,9-dioctylfluorene) ink solution. The formation of the ß-phase poly(9,9-dioctylfluorene) was proved by the present of an absorption peak at 435 nm. The most intense photoluminescence emission was obtained with the collection polarizer oriented parallel to the nanowire long axis, and an emission dichroic ratio of 3.7 was determined.

Stability-improved organic n-channel thin-film transistors with nm-thin hydrophobic polymer-coated high-k dielectrics.

We report on the fabrication of N,N'-ditridecyl-perylene-3,4:9,10-tetracarboxylic diimide-C13 (PTCDI-C13), n-channel organic thin-film transistors (OTFTs) with 30 nm Al(2)O(3) whose surface has been un-modified or modified with hexamethyldisilazane (HMDS) and thin hydrophobic CYTOP. Among all the devices, the OTFTs with CYTOP-modified dielectrics exhibit the most superior device performance and stability. The optimum post-annealing temperature for organic n-channels on CYTOP was also found to be as low as 80 °C, although the post-annealing was previously implemented at 120-140 °C for PTCDI domain growth in general. The low temperature of 80 °C hardly damages the CYTOP/n-channel organic interface which is deformed at a temperature higher than the glass transition temperature of CYTOP (∼110 °C). The pentacenequinone passivation layer turned out to be helpful to keep the interfacial trap density minimum, according to the photo-excited charge collection spectroscopy results for our 80 °C-annealed OTFTs with CYTOP-modified dielectrics.

One-step fabrication of nanowire-grid polarizers using liquid-bridge-mediated nanotransfer molding.

Ag nanowire-grid polarizers (NWGPs) were prepared by a one-step fabrication method, called liquid-bridge-mediated nanotransfer molding (LB-nTM). LB-nTM is a new direct nano-patterning method based on the direct transfer of various materials from a mold to a substrate via liquid layer. We fabricated NWGPs with Ag nanowire arrays (81 nm parallel lines and 119 nm spaces) on 2.5 in. transparent substrates by LB-nTM using an Ag nanoparticle solution. The maximum and minimum transmittances of the Ag NWGP at 800 nm were 80% and 10%, respectively.

High-resolution patterning of silver thin films with a water-mediated metal transfer printing.

We report a direct printing method, water-mediated metal transfer printing (mTP), for generating Ag patterns with a wide range of feature sizes. Water-mediated mTP is based on the direct transfer of a metal thin film from a stamp to a substrate via a water-mediated surface bonding. An Ag thin film is used as a solid "ink" in the mTP, which can be used for the formation of micro- and nanoscale Ag structures. To demonstrate its usefulness, we used the water-mediated mTP to fabricate low voltage ZnO thin-film transistors.

Hierarchical and multifunctional three-dimensional network of carbon nanotubes for microfluidic applications.

Three-Dimensional network of carbon nanotubes: The 3D network of CNTs have hierarchical structures comprised of interconnected SWNTs between Si pillars in microfluidic channels. The Al(2)O(3) coated 3D networks were used for size different nanoparticles filtration and streptavidin capturing in very diluted solution. The 3D network of SWNTs systems will provide a robust multifuncitonal platform for a variety of biomedical and environmental applications.

Direct nanoprinting by liquid-bridge-mediated nanotransfer moulding.

Several techniques for the direct printing of functional materials have been developed to fabricate micro- and nanoscale structures and devices. We report a new direct patterning method, liquid-bridge-mediated nanotransfer moulding, for the formation of two- or three-dimensional structures with feature sizes as small as tens of nanometres over large areas up to 4 inches across. Liquid-bridge-mediated nanotransfer moulding is based on the direct transfer of various materials from a mould to a substrate through a liquid bridge between them. We demonstrate its usefulness by fabricating nanowire field-effect transistors and arrays of pentacene thin-film transistors.

Vapor-phase molecular layer deposition of self-assembled multilayers for organic thin-film transistor.

We report a vapor-phase molecular layer deposition (MLD) of self-assembled multilayer thin films for organic thin-film transistor. In the present MLD process, alkylsiloxane self-assembled multilayers (SAMs) were grown under vacuum by repeated sequential adsorptions of C=C-terminated alkylsilane and aluminum hydroxide with ozone activation. The MLD method is a self-controlled layer-by-layer growth process, and is perfectly compatible with the atomic layer deposition (ALD) method. The SAMs films prepared exhibited good mechanical flexibility and stability, excellent insulating properties, and relatively high dielectric capacitances of 374 nF/cm2 with a high dielectric strength of 4 MV/cm. They were then used as a 12 nm-thick dielectric for pentacene-based thin-film transistors (TFTs), which showed a maximum field effect mobility of 0.57 cm2/V s, operating at -4 V with an on/off current ratio of approximately 10(3).

Low-temperature atomic layer deposition of copper metal thin films: self-limiting surface reaction of copper dimethylamino-2-propoxide with diethylzinc.

A uniform, conformal, pure copper metal thin film was grown at very low substrate temperatures (100-120 degrees C) on Si(100) substrates by atomic layer deposition involving the ligand exchange of [Cu(OCHMeCH(2)NMe(2))(2)] with Et(2)Zn (see scheme). Patterned copper thin films of Cu nanotubes (diameter 150 nm, length 12 microm) were fabricated.

Large-area fabrication of patterned ZnO-nanowire arrays using light stamping lithography.

We demonstrate selective adsorption and alignment of ZnO nanowires on patterned poly(dimethylsiloxane) (PDMS) thin layers with (aminopropyl)siloxane self-assembled monolayers (SAMs). Light stamping lithography (LSL) was used to prepare patterned PDMS thin layers as neutral passivation regions on Si substrates. (3-Aminopropyl)triethoxysilane-based SAMs were selectively formed only on regions exposing the silanol groups of the Si substrates. The patterned positively charged amino groups define and direct the selective adsorption of ZnO nanowires with negative surface charges in the protic solvent. This procedure can be adopted in automated printing machines that generate patterned ZnO-nanowire arrays on large-area substrates. To demonstrate its usefulness, the LSL method was applied to prepare ZnO-nanowire transistor arrays on 4-in. Si wafers.

Gas-phase formation of self-assembled monolayers on MgO for protection against hydration.

The gas-phase adsorption of octyltrichlorosilane onto MgO produces self-assembled monolayers that can provide protection against hydration of the underlying MgO surfaces. MgO thin film has attracted attention for application as a protecting layer of alternating current plasma display panel. On exposure to air, the clean MgO surface interacts with water and quickly hydrates to Mg(OH)2, which reduces the secondary electron emission yield. The gas-phase deposition of octyltrichlorosilane on the clean MgO has produced self-assembled monolayers because of high reactivity of the MgO surface. The ultra-thin organic layer of the octylsiloxane can provide significant protection against hydration to the MgO surface, and improves secondary electron emission yield for the MgO samples. The secondary electron emission coefficient y for the monolayer-coated MgO sample is about 25% higher than that for the clean MgO after 24 hr exposing to air.

Selective atomic layer deposition of metal oxide thin films on patterned self-assembled monolayers formed by microcontact printing.

We demonstrate a selective atomic layer deposition of TiO2, ZrO2, and ZnO thin films on patterned alkylsiloxane self-assembled monolayers. Microcontact printing was done to prepare patterned monolayers of the alkylsiloxane on Si substrates. The patterned monolayers define and direct the selective deposition of the metal oxide thin films using atomic layer deposition. The selective atomic layer deposition is based on the fact that the metal oxide thin films are selectively deposited only on the regions exposing the silanol groups of the Si substrates because the regions covered with the alkylsiloxane monolayers do not have any functional group to react with precursors.

Rapid vapor-phase fabrication of organic-inorganic hybrid superlattices with monolayer precision.

We report a new layer-by-layer growth method of self-assembled organic multilayer thin films based on gas-phase reactions. In the present molecular layer deposition (MLD) process, alkylsiloxane self-assembled multilayers (SAMs) were grown under vacuum by repeated sequential adsorptions of C=C-terminated alkylsilane and titanium hydroxide. The MLD method is a self- limiting layer-by-layer growth process, and is perfectly compatible with the atomic layer deposition (ALD) method. The SAMs films prepared exhibited good thermal and mechanical stability, and various unique electrical properties. The MLD method, combined with ALD, was applied to the preparation of organic-inorganic hybrid nanolaminate films in the ALD chamber. The organic-inorganic hybrid superlattices were then used as active mediums for two-terminal electrical bistable devices. The advantages of the MLD method with ALD include accurate control of film thickness, large-scale uniformity, highly conformal layering, sharp interfaces, and a vast library of possible materials. The MLD method with ALD is an ideal fabrication technique for various organic-inorganic hybrid superlattices.