Flexible nanogap polymer light-emitting diodes fabricated via adhesion lithography (a-Lith)

Abstract

We report the development of coplanar green colour organic light-emitting diodes (OLEDs) based on asymmetric nanogap electrodes fabricated on different substrates including glass and plastic. Using adhesion lithography (a-Lith) we pattern Al and Au layers acting as the cathode and anode electrodes, respectively, separated by an inter-electrode distance of <15 nm with an aspect ratio of up to 10 6 . Spin-coating the organic light-emitting polymer poly(9,9-dioctylfluorene-alt-bithiophene) (F8T2) on top of the asymmetric Al-Au nanogap electrodes results in green light-emitting nanogap OLEDs with promising operating characteristics. We show that the scaling of the OLED's width from 4 to 200 mm can substantially improve the light output of the device without any adverse effects on the manufacturing yield. Furthermore, it is found that the light-emitting properties in the nanogap area differ from the bulk organic film, an effect attributed to confinement of the conjugated polymer chains in the nanogap channel. These results render a-Lith particularly attractive for low cost facile fabrication of nanoscale light-emitting sources and arrays on different substrates of arbitrary size.Nanometer-sized polymer light-emitting diodes (n-PLEDs) have been proposed as light sources in subwavelength scanning near-field optical microscopes as well as in nanoscale photo-patterning to create simultaneously a large number of identical patterns [1,2]. Their unique advantages are colour tunability, versatility in geometrical pattern selection and ease of manufacturing of nanostructured arrays using low cost solution processing on substrates of arbitrary size and shape [3]. From an operational standpoint, miniaturised light-emitting diodes are advantageous to larger area ones, as higher current densities can be sustained thanks to efficient dissipation of Joule heating [4,5]. Indeed a suppression of organic light-emitting diodes (OLEDs) rolloff characteristics has been observed upon narrowing the current injection/transport area down to 50 nm [6]. These developments led to demonstration of low threshold amplified spontaneous emission in light-emitting polymer films [7], which could pave the way to the realisation of electrically pumped organic lasers [8]. Further progress has, however, been hindered by manufacturing challenges, as shadow masking and conventional photolithography cannot produce nanometer-sized electrode feature between different metals, and e-beam lithography is not suitable for upscale while it is often limited to a single electrode material. We have recently introduced adhesion lithography (a-Lith) technique as a viable alternative for the scalable sub-15 nm patterning of asymmetric, i.e. of different work function, coplanar metal electrodes on large area flexible substrates [9]. The asymmetric nature of the electrodes, which is difficult to obtain with other common nanopatterning techniques, allows for a range of electronic nanogap devices to be created via simply depositing a single layer of active material on top of d...

High Responsivity and Response Speed Single‐Layer Mixed‐Cation Lead Mixed‐Halide Perovskite Photodetectors Based on Nanogap Electrodes Manufactured on Large‐Area Rigid and Flexible Substrates

“…The electrical characteristics of the nanogap photodetectors upon scaling the electrodes width are shown in Figure b. The current scales with the coplanar nanogap electrode width in accordance with previous reports of deep UV photodetectors and polymer light‐emitting devices fabricated via a‐Lith. Interestingly, the photocurrent increases with a higher rate than the dark current, as revealed by the slope of the linear fittings of the dark and photocurrent versus diode width plot depicted in Figure c.…”

“…Herein we employ an innovative, simple, low‐cost nanopatterning technique, named adhesion lithography (a‐Lith), for the fabrication of nanogap coplanar electrodes, eliminating thus the need for expensive equipment as well as complicated process steps involved in alternative techniques . Similar nanogap electrode architectures have already been used to develop high frequency diodes, resistive memories, nanoscale polymer light‐emitting diodes and field‐effect transistors on a variety of substrate materials. In this work we combined asymmetric nanogap electrodes composed of either aluminum–gold (Al–Au) or Al–ITO, with the solution processable metal halide perovskite FA 0.83 Cs 0.17 Pb[I 0.9 Br 0.1 ] 3 (termed FACs, where FA is formamidinium), to produce planar photodetectors featuring interelectrode nanogaps of ≈10 nm with widths in the range of 4–50 mm.…”

Air Stable Indium-Gallium-Zinc-Oxide Diodes With a 6.4 GHz Extrinsic Cutoff Frequency Fabricated Using Adhesion Lithography

“…These electrodes can be made from dissimilar metals allowing for the creation of planar Schottky diodes simply via the deposition of a semiconductor material on top of the two asymmetric electrodes. A-Lith has already been used to create high performance devices including photodiodes [15], light emitting diodes [16], memristors [17], TFTs [18] and RF diodes [19]. For RF applications, the fact that the asymmetric electrodes are planar and have a nanoscale channel allows for higher cut-off frequencies due to a reduced device area and hence a smaller junction capacitance.…”

Fabrication of Size-Controlled Metallic Nanogaps down to the Sub 3-Nm Level

“…One particularly effective peeling-based technique known as adhesion lithography (or "a-lith") uses self-assembled monolayers (SAMs) as adhesion modifiers, allowing MNGs with gap-widths as low as 10 nm to be fabricated using a small number of simple processing steps and inexpensive equipment. 47,48,[49][50][51][52][53][54][55][56][57][58] Until now, the reported gap-widths obtained by a-lith have been much higher than the 2-nm length of the SAM molecule, which is presumed to determine the absolute resolution limit of the technique. Hence, it has not been possible to apply adhesion lithography to applications that require the control of materials properties or light-matter interactions at extreme (sub-5-nm) length-scales, e.g.…”