Kyung Hee University · Engineering
Professor Jung Hwa Seo's research lab specializes in the design, synthesis, and application of conjugated polyelectrolytes (CPEs) for advanced organic optoelectronic devices. The lab focuses on using CPEs as interfacial engineering materials to optimize charge injection and transport in devices such as organic solar cells, thin-film transistors, and light-emitting transistors. By manipulating the ionic character, counterions, and molecular architecture of CPEs, the group achieves precise control over electronic energy levels and interfacial dipoles, enabling high-performance, solution-processed devices. Their work emphasizes the fundamental understanding of structure-property relationships at organic/metal and organic/organic interfaces to advance next-generation flexible and low-cost optoelectronics.
Figures are computed from collected data and may differ slightly.
The power conversion efficiencies of bulk heterojunction (BHJ) solar cells can be increased from 5 to 6.5% by incorporating an ultrathin conjugated polyelectrolyte (CPE) layer between the active layer and the metal cathode. Poly[N-9''-heptadecanyl-2,7-carbazole-alt-5,5-(4',7'-di-2-thienyl-2',1',3'-benzothiadiazole)] (PCDTBT) and [6,6]-phenyl C(71) butyric acid methyl ester (PC(71)BM) were chosen for the photoactive layer. CPEs with cationic polythiophenes, in both homopolymer and block copolymer
The chemical structures and electronic structures at conjugated polyelectrolyte/Au interfaces demonstrate that conjugated polyelectrolytes with identical backbones but different pendant charges and charge-compensating ions exhibit different electronic properties. This finding shows that counterions and backbone charges enable control of the electronic and chemical nature of critical device interfaces.
The electronic properties of conjugated polyelectrolytes (CPEs) with poly(fluorene-co-phenylene) backbones and different counterions and charges have been investigated using absorption and ultraviolet photoelectron spectroscopy (UPS). The optical energy band gap of CPEs depends mainly on their conjugated backbone and are nearly insensitive to the charges or counterions. UPS measurements reveal that electron injection from Au to polymers with cationic groups is more efficient than for the neutral
To improve injection in n-type organic thin film transistors (OTFTs), a thin conjugated polyelectrolyte (CPE) layer was interposed between electrodes and the semiconductor layer. OTFTs were fabricated with [6,6]-phenyl-C(61) butyric acid methyl ester (PCBM) and Au source and drain contacts. We demonstrate that the insertion of CPEs beneath top-contact Au source/drain electrodes can be a very effective strategy for improving the carrier injection and reducing turn-on threshold voltages of n-chann
Abstract Improved performance of p ‐type organic light‐emitting transistors (OLETs) is demonstrated by introducing a conjugated polyelectrolyte (CPE) layer and symmetric high work function (WF) source and drain metal electrodes. The OLET comprises a tri‐layer film consisting of a hole transporting layer, an emissive layer, and a CPE layer as an electron injection layer. The thickness of the CPE layer is critical for achieving good performance and provides an important structural handle for consi
This feature article presents a short review of the recent developments in the synthesis of conjugated polyelectrolytes (CPEs) along with their applications in organic optoelectronic devices with particular focus on the molecular structures of CPEs with ionic functionality, synthetic approaches, and their utilization as an interfacial layer. The orthogonal solubility of the CPEs allows the simple preparation of multilayer organic devices by solution casting on top of a nonpolar organic photoacti
A new donor–acceptor type small molecule with dithienothiophene and diketopyrrolopyrrole units has been synthesized for application in organic solar cells. In order to optimize the nanoscale morphology of the small molecule solar cells, additives such as 1,8-diiodooctane (DIO) and 1-chloronaphthalene (CN) are used. The use of CN significantly suppresses molecular aggregation and allows suitable phase separation, enhancing power conversion efficiency from 0.5% to 2.2%.
The structural and electrical properties of organic thin-film transistors with rubrene/pentacene and pentacene/rubrene bilayered structures were investigated using x-ray diffraction, atomic force microscopy, and x-ray emission spectroscopy. High-quality rubrene thin films with orthorhombic structure were obtained in the rubrene/pentacene bilayer while the pentacene/rubrene bilayer only had an amorphous rubrene phase present. The rubrene/pentacene thin-film transistor shows more desirable current
The effect of solvent additives on the performance of 6,13-bis(triisopropylsilylethynyl) pentacene (TIPS-pentacene) field effect transistors (FETs) was investigated. Hole mobilities increased from 0.10 cm2 V−1 s−1 for pristine devices to 0.73 or 0.71 cm2 V−1 s−1, when TIPS-pentacene FETs were processed with diphenyl ether (DPE) or chloronaphthalene (CN), respectively. In order to examine the impact of additives on the surface morphology, molecular ordering and crystallinity of TIPS-pentacene, sc
We report on solution-processed light emitting field-effect transistors (LEFETs) that incorporate symmetric high work function (WF) source and drain metal electrodes. A key architectural design is the incorporation of a conjugated polyelectrolyte (CPE) electron injection layer atop the emissive layer. The device structure also comprises a hole-transporting layer underneath the emissive layer. Both holes and electrons are injected from stable, high WF metal though the CPE layer leading to electro
Open papers in the app to read, cite, and organize with AI.
