Gyeong Eun Lim

Nonconjugated anionic polyelectrolyte as an interfacial layer for the organic optoelectronic devices.

A nonconjugated anionic polyelectrolyte, poly(sodium 4-styrenesulfonate) (PSS-Na), was applied to the optoelectronic devices as an interfacial layer (IFL) at the semiconducting layer/cathode interface. The ultraviolet photoelectron spectroscopy and the Kelvin probe microscopy studies support the formation of a favorable interface dipole at the organic/cathode interface. For polymer light-emitting diodes (PLEDs), the maximum luminance efficiency (LEmax) and the turn-on voltage (Von) of the device with a layer of PSS-Na spin-coated from the concentration of 0.5 mg/mL were 3.00 cd/A and 5.5 V, which are dramatically improved than those of the device without an IFL (LEmax = 0.316 cd/A, Von = 9.5 V). This suggests that the PSS-Na film at the emissive layer/cathode interface improves the electron injection ability. As for polymer solar cells (PSCs), the power conversion efficiency (PCE) of the device with a layer of PSS-Na spin-coated from the concentration of 0.5 mg/mL was 2.83%, which is a 16% increase compared to that of the PSC without PSS-Na. The PCE improvement is mainly due to the enhancement of the short-circuit current (12% increase). The results support that the electron collection and transporting increase by the introduction of the PSS-Na film at the photoactive layer/cathode interface. The improvement of the efficiency of the PLED and PSC is due to the reduction of the Schottky barrier by the formation of a favorable interface as well as the better Ohmic contact at the cathode interface.

Enhancing the efficiency of opto-electronic devices by the cathode modification

A non-conjugated polymer with a polar hydroxyl group as a side group, poly(vinyl alcohol) (PVA), is applied to polymer solar cells (PSCs) and polymer light-emitting diodes (PLEDs) as a buffer layer at the active layer/cathode interface. The best power conversion efficiency (PCE) of PSCs with the PVA film as a cathode buffer layer is 3.27%, which is a 27% increase compared to that of PSCs without the PVA film (2.58%). The PCE improvement is due to enhancement of the short circuit current, the fill factor, and the open circuit voltage, simultaneously. Also, the performances of polymer light-emitting diodes with the PVA film as a cathode buffer layer are better than those of the devices without PVA. Improvement of the performances of the devices is due to the fact that the PVA film reduces a Schottky barrier by the formation of favorable interface dipoles and improves the interface properties.

Diketopyrrolopyrrole-based Small Molecule for Application in Solution Processed Organic Solar Cells

A novel donor-π bridge - acceptor (A)-π bridge - donor type molecule (PCTDPP20) with planar core based on diketopyrrolopyrrole (DPP) and carbazole is synthesized by the Suzuki coupling reaction. We introduce phenyl rings to extend the π-conjugation length as a π-bridge. The HOMO and LUMO energy levels of PCTDPP20 are −5.13 and −3.57 eV, respectively. From the UV-Vis spectra, we confirm that the maximum absorption wavelgth (λmax) of the PCTDPP20 annealed film at 100°C is red-shifted about 30 nm and the absorption intensity at 600 ∼ 650 nm increase compared to that of as-spun film. And the OFET based on PCTDPP20 annealed at 100°C exhibits a highest hole mobility of 1.6 × 10−4 cm2/Vs together with a Ion/Ioff ratio of 1.0 × 104 and a Vth of 14 V. Also, the photovoltaic properties are investigated in the device structure of ITO/PEDOT:PSS/PCTDPP20:PC60BM (with different blend ratios)/Al. Among the OSCs, PCTDPP20:PCBM weight ratio of 1:0.8 and termal annealing process at 100°C for 10 min are optimum belnd ratio and temperature, respectively. This device shows the best performance with a highest PCE of 0.95% a Jsc of −2.69 mA/cm2, a Voc of 0.79 V and a fill factor of 44.5%.

Chloroprene rubber modified by nanosilica for performance adhesion strength

ABSTRACT In this study, chloroprene rubber (CR) /silica nanocomposites prepared by dispersing nanosilica in CR was applied as a primer and its adhesion properties were examined. The structure of CR/silica nanocoposite was analyzed by Fourier transform-infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), and energy dispersive spectroscopy (EDS) were used to confirm the morphology and silica content of the CR/silica nanocomposite. The SEM results indicated that the sample prepared with a silica content of 4 phr was the most homogenously dispersed. Contact angle and pencil hardness measurements indicated that the hydrophobicity and the hardness of the CR/silica nanocomposite increased with increase in the silica content. The peel strength was the highest at a silica content of 4 phr, and the initial peel strength of P-4 sample (2.9 kgf/inch) was 50% higher than that of the P-0 sample.

Solution-processed small-molecule organic solar cells based on diketopyrrolopyrrole and perlyene derivatives with coplanar structures

ABSTRACT A series of small-molecules (SMs) based on coplanar perylene unit coupled with diketopyrrolopyrrole chromophoric core exhibit broad absorption in the range of 500–800 nm and low bandgap energise of 1.6–1.7 eV. The power conversion efficiency approximately reach at 0.4% under 1.5 G illumination is achieved for organic solar cells based on a small-molecule bulk heterojunction system consisting of SMs as a donor and [6,6]-phenyl-C61-butyric acid methyl ester (PC61BM) as an acceptor.