Letter pubs.acs.org/NanoLett
Cross-Stacked Single-Crystal Organic Nanowire p−n Nanojunction Arrays by Nanotransfer Printing Kyung Sun Park,† Ki Seok Lee,† Chan-mo Kang,‡ Jangmi Baek,† Kyu Seok Han,† Changhee Lee,*,‡ Yong-Eun Koo Lee,† Youngjong Kang,† and Myung Mo Sung*,† †
Department of Chemistry, Hanyang University, Seoul 133-791, Korea Department of Electrical and Computer Engineering, Inter-university Semiconductor Research Center, Seoul National University, Seoul 151-744, Korea
‡
S Supporting Information *
ABSTRACT: We fabricated cross-stacked organic p−n nanojunction arrays made of single-crystal 6,13-bis(triisopropylsilylethynyl) pentacene (TIPS-PEN) and fullerene (C60) nanowires as p-type and n-type semiconductors, respectively, by using a nanotransfer printing technique. Single-crystal C60 nanowires were synthesized inside nanoscale channels of a mold and directly transferred onto a desired position of a flexible substrate by a lubricant liquid layer. In the consecutive printing process, single-crystal TIPS-PEN nanowires were grown in the same way and then perpendicularly aligned and placed onto the C60 nanowire arrays, resulting in a cross-stacked single-crystal organic p−n nanojunction array. The cross-stacked single-crystal TIPS-PEN/C60 nanowire p−n nanojunction devices show rectifying behavior with on/off ratio of ∼13 as well as photodiode characteristic with photogain of ∼2 under a light intensity of 12.2 mW/cm2. Our study provides a facile, solution-processed approach to fabricate a large-area array of organic crystal nanojunction devices in a desired arrangement for future nanoscale electronics. KEYWORDS: Single-crystal organic nanowire, p−n nanojunction, organic diode, direct printing
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they have great advantages such as lightweight, mechanical flexibility, low-cost production, and ease of property optimization from modification of their molecular design and chemical composition.2,19,20 Nevertheless, there are only few efficient methods to prepare and/or arrange nanoscale junctions from pure organic semiconducting materials for desired device architectures comprised of a variety of homoand/or heterojunction configurations. Recently, nanowirebased single-crystal organic p−n junctions were synthesized to have structures of either core−shell coaxial nanowires or double layered nanoribbons, showing high promise for their applications in fundamental science and new device technologies.21,22 These nanowire p−n junctions, however, are produced through vapor phase processes that require high cost and long process time. The materials to prepare these nanowire p−n junctions are limited to only a few compounds as well. Moreover, deployment of individual nanosized p−n junctions onto desired locations of a device in a desired arrangement was not achieved for practical applications. So far, no study has been reported on making p−n heterojunction devices made of two different single-crystal organic nanowires
ne-dimensional (1D) nanostructures, such as nanowires and nanotubes, have received a high interest as versatile building blocks for sophisticated nanodevices in a variety of fields, especially electronic applications.1−3 Hierarchical assemblies of the 1D nanostructures have a great potential in future electronic devices by enabling drastically enhanced data storage in a limited space. There have been a broad range of studies to prepare assemblies of metallic/semiconducting nanowires for use in various electronic devices.4−12 For instance, crossstacked nanowire junction arrays are one example to provide a generic possibility for fabrication of high-density integrated devices with an individual addressable function at each cross point.4−6,11 p−n heterojunctions, an assembly made of p-type and n-type semiconductors, are one of the most basic elements that are used to fabricate electronic devices such as diodes, bipolar transistors, photodetectors, light-emitting diodes, and solar cells.13 During the past decade, p−n heterojunctions based on 1D nanowires have been prepared either by stacking two premade nanowires or by synthesis.6,14−18 The nanowirebased p−n heterojunctions have successfully demonstrated their rectification and light-emitting behaviors as well as their use for the model system in fundamental studies. However, most of the heterojunction nanowires are made from only inorganic materials or organic−inorganic hybrid. Importantly, organic semiconducting nanowires have emerged as an attractive material in modern electronics as © 2014 American Chemical Society
Received: September 16, 2014 Revised: November 6, 2014 Published: December 3, 2014 289
dx.doi.org/10.1021/nl5035623 | Nano Lett. 2015, 15, 289−293
Nano Letters
Letter
Figure 1. Schematic illustration of the procedure used to fabricate a cross-stacked organic nanowire p−n nanojunction array by LB-nTM. First, single-crystal C60 nanowires (orange color), synthesized and crystallized in nanoscale channels of a mold, are directly printed on a desired position of a substrate by LB-nTM. Subsequently, single-crystal TIPS-PEN nanowires (blue color), grown in the same way, are perpendicularly aligned to the C60 nanowire arrays and then printed onto it. Finally, metal electrodes are deposited by a thermal evaporation method. The molecular structures and the energy level diagram of the two nanowire materials are also given.
width of 100 nm and a height of 100 or 200 nm, made by ebeam lithography. For the first layer on the substrate, a C60 ink solution is applied on a 100 nm-high nanoline patterned PUA mold, filling only the intaglio channels due to selective inking based on discontinuous dewetting.26 The C60 ink solution inside each of the intaglio nanoscale channels is then slowly solidified into a single-crystal C60 nanowire through selfassembling and crystallization of C60 molecules while drying at mild temperature (
