Seunghyup Yoo

We have fabricated an efficient organic photovoltaic cell based on a heterojunction of pentacene and C60. Photocurrent action spectra exhibit broad light-harvesting throughout the visible spectrum with a peak external quantum efficiency (EQE) of 58±4% at short-circuit condition. Modeling studies indicate that this high EQE can be partly attributed to the large exciton diffusion length in the pentacene film as well as efficient dissociation of excitons at the pentacene/C60 heterojunction.

Doping improves performance. N- or B-doped carbon nanotubes (CNTs) uniformly dispersed in the active layer of P3HT/PCMB (poly (3-hexylthiophene/[6,6]-phenyl-C61-butyric acid methyl ester) bulk-heterojunction solar cells selectively enhance electron or hole transport and eventually help carrier collection. Specifically, the incorporation of 1.0 wt% B-doped CNTs results in balanced electron and hole transport and accomplishes a power conversion efficiency improvement from 3.0% (without CNTs) to 4.

Pulse oximetry sensors have been playing a key role as devices to monitor elemental yet critical human health states. Conventional pulse oximetry sensors, however, have relatively large power consumption, impeding their use as stand-alone, continuous monitoring systems that can easily be integrated with everyday life. Here, we exploit the design freedom offered by organic technologies to realize a reflective patch-type pulse oximetry sensor with ultralow power consumption. On the basis of flexib

We present studies of the current–voltage characteristics of organic solar cells based on heterojunctions of pentacene and C60 as a function of illumination intensity. The photovoltaic response at a given illumination level is parameterized and modeled using the equivalent circuit model developed for inorganic pn-junction solar cells. Reduction in shunt resistance and increase in diode reverse saturation current density are observed upon increase of the light intensity. We demonstrate that this

A highly conductive polymer layer coated on a microstructured indium tin oxide (ITO) electrode is proposed as a simple way to enhance outcoupling in organic light-emitting diodes. The relatively low refractive index of the conductive polymer provides an index contrast between the organic and ITO layers so that structuring of ITO electrodes can result in a significant optical effect.

Abstract A novel approach to highly efficient, blue thermally activated delayed fluorescent (TADF) emitters is proposed. A series of ortho ‐carbazole‐appended triarylboron compounds ( 1 – 5 ) are prepared with various substituents, including tert ‐Bu, Me, and OMe, introduced to the carbazole donor and/or to the dimesitylphenylboron (PhBMes 2 ) acceptor. Depending on the substituents on the donor and/or acceptor moieties, the emission color is finely tuned over the entire blue region from sky blu

An industrial-grade polyethylene naphthalate (PEN) substrate is explored as a simple, cost-effective platform for high-efficiency organic light-emitting diodes (OLEDs). Its high refractive index, combined with the built-in scattering properties inherent to the industrial-grade version, allows for a significant enhancement in outcoupling without any extra structuring or special optical elements. Flexible, color-stable OLEDs with efficiency close to 100 lm W(-1) are demonstrated.

Abstract Graphene quantum dots (GQDs) have attracted great attention as next‐generation luminescent nanomaterials due to the advantages of a low‐cost process, low toxicity, and unique photoluminescence (PL). However, in the solid‐state, the strong π−π stacking interactions between the basal planes of GQDs lead to aggregation‐caused PL quenching (ACQ), which impedes practical application to light‐emitting devices. Here, surface functionalized GQDs (F‐GQDs) by polyhedral oligomeric silsesquioxane