Paik-Kyun Shin

Examining the effect of additives and thicknesses of hole transport layer for efficient organic solar cell devices

Poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS), a conducting polymer, has been receiving a great deal of attention for next generation optoelectronic organic devices. In this report, we discuss the effect of additives along with the thickness of PEDOT:PSS layers on the power conversion efficiency of organic solar cell devices. PEDOT:PSS films treated with high boiling point solvents of dimethyl sulfoxide (DMSO) and ethylene glycol (EG) show a significant enhancement in electrical conductivity without compromising flexibility or optical transparency. The conductivity increased from 0.5 to 517 and 724 S/cm after once and thrice treatment with 4 vol. % EG, respectively. The as-prepared and additives-treated PEDOT:PSS films deposited on glass substrates have been investigated by optical spectroscopy, micro-Raman spectroscopy and atomic force microscopy (AFM). The results indicate that structural and morphological changes were induced by the additive processes. By using DMSO and EG treated PEDOT:PSS as a hole transport layer, organic solar cells with a Poly[[9-(1-octylnonyl)-9H-carbazole-2,7-diyl]-2,5-thiophenediyl-2,1,3-benzothiadiazole-4,7-diyl-2,5-thiophenediyl]:[6,6]-phenyl-C71-butyric acid methyl esters (PCDTBT:PC71BM) bulk heterojunction have been fabricated on indium-tin-oxide (ITO) coated glass substrates. The high power conversion efficiency (PCE) of 5.17%, and 5.69%, were observed for PEDOT:PSS hole transport layers treated with DMSO and EG respectively, even though the devices were prepared in air atmosphere.

Comparison of properties of polymer organic solar cells prepared using highly conductive modified PEDOT:PSS films by spin- and spray-coating methods

Bulk heterojunction (BHJ) solar cells have made great progress over the past decade and consequently are now attracting extensive academic and commercial interest because of their potential advantages: lightweight, flexible, low cost, and high-throughput production. Polymer conductivity is a key factor for improving the performance of electronic and photonic devices. Poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) is promising for use as a next-generation transparent electrode of optoelectronic devices. In this research, we compare the effect of nanomorphology on conductivity, and power conversion efficiency of polymer organic solar cells prepared by the spin- and spray-coating methods. To improve the conductivity of spray-deposited PEDOT:PSS, we modified the PEDOT:PSS films by simple UV irradiation and by UV irradiation with treatment using various solvents such as methanol, ethanol, acetone, acetonitrile, hydrochloric acid, and sulfuric acid to form a hole transport layer (HTL). The active layer of PTB7:PC70BM is spray-coated on top of the PEDOT:PSS layer. The films were examined by optical spectroscopy, micro-Raman spectroscopy, and conductivity measurements. The surface morphology of the deposited films was examined by atomic force microscopy (AFM). The current density–voltage (J–V) characteristics were measured under illumination with simulated solar light at 100 mW/cm2 (AM 1.5G) using an oriel 1000 W solar simulator. The obtained results are expected to have a considerable impact and suggest a bright future for organic polymer solar cells.

Facile biosynthesis, characterization, and solar assisted photocatalytic effect of ZnO nanoparticles mediated by leaves of L. speciosa

Synthesis of metal oxide nanoparticles using novel methodologies always attracts great importance in research. The use of plant extract to synthesize nano-particle has been considered as one of the eco-friendly methods. This paper describes the biosynthetic route of preparation of zinc oxide nanoparticles (ZnO NPs) from the Lagerstroemia speciosa leaf extract. This approach appears to be low-cost preparation and alternative method to conventional methods. Highly stable and hexagonal phase ZnO NPs with average particle size of 40nm were synthesized and characterized by UV-Vis absorption spectroscopy (surface Plasmon resonance), Fourier transform infrared spectroscopy (surface functionalities), X-ray Diffraction analysis (crystallinity), TEM and SEM (size and morphology), Energy Dispersive X-ray spectroscopy (elemental composition), Thermogravimetric analysis (weight loss) and Zeta potential (stability). The preliminary phytochemical experiments identify the possible chemical groups present in leaves extract. The photocatalytic properties of ZnO NPs were studied using UV-Vis spectroscopy by exposing methyl orange to sunlight and it is found to be degraded up to 93.5% within 2h. The COD values were significantly reduced from 5600mg/L to 374mg/L after 100min of solar radiation. The hemolytic activity of synthesized zinc oxide nanoparticles was performed on human erythrocyte cells. Thus the present study provides a simple and eco-friendly method for the preparation of multifunctional property of ZnO NPs utilizing the biosynthetic route.

Carbon Nanotube Interconnection and Its Electrical Properties for Semiconductor Applications

In this work, the integration and its electrical properties of a carbon nanotube (CNT) interconnect for semiconductor applications are presented. A series array of 1000 vias made of vertically grown CNTs was achieved with uniform electrical resistance within the wafer. The integration of CNT interconnection was implemented with conventional semiconductor processes by following sequential steps: bottom electrode and via hole patterning, CNT growth and planarization, and top electrode patterning on the wafer. Multi walled CNTs (MWCNTs) as the interconnection, titanium nitride as the bottom electrode, and aluminum with a titanium contact layer as the top electrode were used. We demonstrated well-defined CNT via interconnect with 700 nm via holes on a full-sized wafer. A via resistance of 350 kΩ and a CNT density of 2.7×1010/cm2 were achieved with a small resistance variation within the wafer, which also corresponded to 51.3 kΩ per MWCNT 10 nm in diameter. Possible approaches to further decrease of electrical resistance are suggested.

Performance evaluation of PTB7 : PC71BM based organic solar cells fabricated by spray coating method using chlorine free solvent

The PTB7 : PC71BM polymer based solar cells have been successfully fabricated by spin and spray coating technique using chlorine-free solvent (xylene), which are desirable to reduce environmental issues. The surface morphology of fabricated film characterized by AFM reveals that the surface morphology of the film is uniform and smooth when xylene is used as compared with chlorobenzene. The highest power conversion efficiency (PCE) (5.07 ± 0.6) was achieved using spray-coating technique than that of spin coating technique (PCE of 4.47 ± 0.6). The enhancement in the performance of the polymer solar cell could be attributed to the improved charge carrier transportation due to additive. The combination of chlorine-free solvent and spray-coating method minimize the waste material and reduce the environmental problem in large-area production of organic solar cells (OSCs).

Fabrication and Characterization of Ni-Cr Alloy Thin Films for Application to Precision Thin Film Resistors

Ni(75 wt.%)-Cr(20 wt.%)-Al(3 wt.%)-Mn(4 wt.%)-Si(1 wt.%) alloy thin films were prepared using the DC magnetron sputtering process by varying the sputtering conditions such as power, pressure, substrate temperature, and post-deposition annealing temperature in order to fabricate a precision thin film resistor. For all the thin film resistors, sheet resistance, temperature coefficient of resistance (TCR), and crystallinity were analyzed and the effects of sputtering conditions on their properties were also investigated. The oxygen content and TCR of Ni-Cr-Al-Mn-Si resistors were decreased by increasing the sputtering pressure. Their sheet resistance, TCR, and crystallinity were enhanced by elevating the substrate temperature. In addition, the annealing of the resistor thin films in air at a temperature higher than 300℃ lead to a remarkable rise in their sheet resistance and TCR. This may be attributed to the improved formation of NiO layer on the surface of the resistor thin film at an elevated temperature.

Floating-gate type organic memory device with organic insulator film of plasma polymerized styrene

Plasma polymerized styrene (ppS) thin films were prepared and used as gate insulator and tunneling layer in a floating-gate type organic memory device. To investigate feasibility of the ppS thin film for application in non-volatile organic memory, an organic thin film transistor (OTFT) and a floating-gate type organic memory device were fabricated. Current–voltage (I–V) characteristics of the OTFT and floating-gate type organic memory device were comparatively investigated, and hysteresis in the I–V characteristics of both devices was studied. A pseudo-charge-storage phenomenon was found for the ppS insulator thin film in the OTFT and floating-gate type organic memory device. The floating-gate type organic memory device revealed a reasonable hysteresis voltage of 27 V. It was confirmed that the ppS could be applied to fabricate an alternative floating-gate type organic memory device with promising memory function.

Process Condition Considered Preparation and Characterization of Plasma Polymerized Methyl Methacrylate Thin Films for Organic Thin Film Transistor Application

Plasma polymerized methyl methaclylate (ppMMA) thin films were prepared with various process conditions such as inductively coupled plasma (ICP) power, substrate bias power, working pressure, substrate heating temperature, substrate position, and monomer flow rate. Thickness, surface morphology, dielectric constant, and leakage current of the ppMMA thin films were investigated for application to organic thin film transistor as gate dielectric. Deposition rate of over 8.6 nm/min, dielectric constant of 3.4, and leakage current density of 8.9 ×10-9 A/cm-2 at electric field of 1 MV/cm were achieved for the ppMMA thin film prepared at the optimized process condition: plasma power of RF 100 W; Ar flow rate of 20 sccm; working pressure of 5 mTorr; substrate temperature of 100 °C; substrate position of 100 mm. The ppMMA thin film was then applied to pentacene based organic thin film transistor (OTFT) device fabrication. The OTFT device with 80 nm thick pentacene semiconductor layer showed field effect mobility of 0.144 cm2 V-1 s-1 and threshold voltage of -1.72 V.

Characterization of Organic Thin Film Solar Cells of PCDTBT : PC71BM Prepared by Different Mixing Ratio and Effect of Hole Transport Layer

The organic thin film solar cells (OTFSCs) have been successfully fabricated using PCDTBT : PC71BM with different mixing ratios (1 : 1 to 1 : 8) and the influence of hole transport layer thickness (PEDOT : PSS). The active layers with different mixing ratios of PCDTBT : PC71BM have been fabricated using o-dichlorobenzene (o-DCB). The surface morphology of the active layers and PEDOT : PSS layer with different thicknesses were characterized by AFM analysis. Here, we report that the OTFSCs with high performance have been optimized with 1 : 4 ratios of PCDTBT : PC71BM. The power conversion efficiency (PCE = 5.17%) of the solar cells was significantly improved by changing thickness of PEDOT : PSS layer. The thickness of the PEDOT : PSS layer was found to be of significant importance; the thickness of the PEDOT : PSS layer at 45 nm (higher spin speed 5000 rpm) shows higher short circuit current density () and lower series resistance () and higher PCE.

Floating-Gate Type Organic Memory with Organic Insulator Thin Film of Plasma Polymerized Methyl Methacrylate

To fabricate organic memory device by entirely dry process, plasma polymerized methyl methacrylate (ppMMA) thin films were prepared and they were used as both tunneling layer and gate insulator layer in a floating-gate type organic memory device. The ppMMA thin films were prepared with inductively coupled plasma (ICP) source combined with stabilized monomer vapor control. The ppMMA gate insulator thin film revealed dielectric constant of 3.75 and low leakage current of smaller than 10-9 A/cm. The floating-gate type organic memory device showed promising memory characteristics such as memory window value of 12 V and retention time of over 2 h, where 60 V of writing voltage and -30 V of erasing voltage were applied, respectively.