Changsoon Kim

A simple and general postdeposition electrode patterning technique for active organic electronic devices is demonstrated and is applied to patterning the metal cathodes of organic light-emitting devices. Selective lift-off of the metal cathode layer is achieved by pressing a prepatterned, metal-coated silicon stamp on the unpatterned device layers. Under pressure, the metal coating on the stamp cold-welds to the metal cathode coating the underlying organic films. Subsequent separation of the sta

We demonstrate a patterning method capable of producing features of submicron scale based on the transfer of a metal film from a stamp to a substrate assisted by cold welding. The patterned metal film can be used as an etch mask to replicate the pattern on the substrate, or the film itself can serve as contact electrodes for a wide range of electronic devices. We demonstrate the versatility of the technique by fabricating a polymer grating on SiO2 with lateral dimensions <80 nm and a patt

While cracks are usually considered detrimental, crack generation can be harnessed for various applications, for example in ceramic materials, via directing crack propagation and crack opening. Here, we find that electron beam irradiation prompts a crack suppression phenomenon in a copper (Cu) thin film on a polyimide substrate, allowing for the control of crack formation in terms of both location and shape. Under tensile strain, cracks form on the unirradiated region of the Cu film whereas crac

Circularly polarized luminescence (CPL) enables promising applications in asymmetric photonics. However, the performances of CPL molecules do not yet meet the requirements of these applications. The shortcoming originates from the trade-off in CPL between the photoluminescence quantum yield (PLQY) and the photoluminescence dissymmetry factor ( g PL ). In this study, we developed a molecular strategy to circumvent this trade-off. Our approach takes advantage of the strong propensity of [Pt(N^C^N)

at a wavelength of 540 nm, respectively. Although challenges remain in the development of polymer hosts for CP PLEDs, our research demonstrates that chiroptical performances can be amplified by using chiral polymer hosts.

We demonstrate the localized patterning of organic thin films based on direct material transfer from a stamp to a substrate. This process, based on van der Waals bonding between contacting organic films, extends the range of application of patterning via stamping to devices where the active organic materials must be locally deposited on the substrate. A mechanical analysis combined with finite element numerical simulations successfully describes the details of the material transfer process over

ABSTRACT In this article, we developed a dual‐band band‐pass filter (DB‐BPF) based on stepped impedance resonators (SIRs) using coupled feeding lines input and output ports. The developed filter allows the adjustment of the frequency and the bandwidth of the upper band (3.8 GHz) and the lower band (2.4 GHz). The transmission coefficients of the DB‐BPF are improved by maximizing the coupling between the SIRs. Furthermore, the capability of the rejection band is increased and the insertion losses

To build a large-scale quantum information processor (QIP) based on trapped ions or neutral atoms, integrated optical systems capable of delivering laser beams to multiple target locations are necessary. We consider a beam-shifting element consisting of a tilting micromirror located at the focal point of a lens, as a fundamental building block for such a system. We explore the design space of the micromirrors and characterize their dc, frequency, and transient responses. The fastest mirror featu

Abstract Multilayer structures involving solution-deposited polymer films are difficult to fabricate, not allowing for unrestricted designs of polymer-based optoelectronic devices required for maximizing their performance. Here, we fabricate a hybrid organic tandem solar cell whose top and bottom subcells have polymer:fullerene and small molecules active layers, respectively, by a solvent-free process based on transferring the polymer:fullerene layer from an elastomeric stamp onto a vacuum-depos

When a perovskite precursor solution is electrosprayed using the conventional method where the nebulization of the solution is primarily governed by electrostatics, its high electrical conductivity tends to cause electrospray instabilities and thus makes high-quality perovskite films very difficult to obtain. Here, we report high-throughput fabrication of efficient perovskite solar cells (PSCs) whose CH 3 NH 3 PbI 3– x Cl x films are deposited using a sheath-gas-assisted electrospray system. Our

It is demonstrated that a stamp composed of a poly(dimethylsiloxane) (PDMS) bulk and perfluoropolyether (PFPE) coating fabricated by a simple dip-coating method has the following properties that are ideal for the transfer patterning of various materials. Deposited by a condensation reaction between PDMS and PFPE molecules as well as the adjacent PFPE molecules, the PFPE coating has a strong adhesion to the PDMS surface and strong internal cohesion, while providing a low energy surface. Furthermo

We propose a lateral-tandem organic photovoltaic system consisting of a dispersive-focusing element and continuously-tuned, series-connected sub-cells. The proposed system overcomes the efficiency limitation of organic photovoltaic devices by spectral re-distribution of incoming solar photons and their delivery to the wavelength-matched, resonant sub-cells. By numerical simulations, we demonstrate that optical resonance in a microcavity sub-cell with a metal/organic multilayer/metal structure ca