Papers by Author: Chi Chin Yap

Abstract: One dimensional ZnO nanorod has been extensively studied in sensor application due to its unique properties in direct energy band gap and high binding energy. In this report, ZnO nanorod arrays were synthesized via hydrothermal approach. Highly oriented (002) nanorods array with diameter of (22.42 ± 1.40) nm was successfully grown on the quartz surface. A low cost and room temperature optical based NO sensor was introduced. ZnO nanorods array show a high sensitivity upon the NO gas which is 20.1 % within 3 minutes. This newly established method can be potentially used in detection of other toxicity gas.

Abstract: The effect of laser dye (Fluorol 7GA) content on the optoelectronic properties of Poly ( 9,9'-di-n-octylfluorenyl-2.7-diyl) conjugated polymer (PFO) based OLEDs has been investigated. The PFO/Fluorol 7GA hybrids with weight ratios between 0.1 and 5 wt. % were prepared using the solution blending method. The blends were deposited on ITO (Indium Tin Oxide) substrate using spin-coating technique. Thin layer of aluminum was deposited on top of the films to act as electrode. Absorption and photoluminescence techniques were used to investigate the energy transfer in the blend. The device performance was investigated in terms of electroluminescence, luminance, luminance efficiency and color measurements. The Förster energy transfer occurred in the blends as evidence from optical spectroscopy and average distance between donor and acceptor molecules. The optimum ratio was 0.5 wt. % where highest enhancement in OLEDs performance was observed. These were attributed to the synchronize effect of efficient energy transfer from PFO to Fluorol 7GA and carrier trapping processes.

Abstract: The effects of reactant concentration on the growth of ZnO nanostructures and the photovoltaic performance of inverted organic solar cells based on a blend of poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene] (MEHPPV) as donor and (6,6)-phenyl-C61 butyric acid methyl ester (PCBM) as acceptor with a structure of FTO/ZnO nanostructures/MEHPPV:PCBM/Ag utilizing ZnO nanostructures as electron collecting layer and silver as a hole collecting electrode were investigated. The ZnO preparation consisted of ZnO nanoparticles seed layer coating and followed by ZnO nanostructures growth in equimolar aqueous solution of zinc nitrate hexahydrate (0.02-0.08 M) and hexamethylenetetramine (0.02-0.08 M). ZnO nanorods having diameter of 50-70 nm and with length up to 120 nm were obtained at reactant concentration of 0.04 M. The ZnO nanorods started to merge with each other and formed irregular nanostructures vertically on the substrates at higher reactant concentrations of 0.06 M and 0.08 M. The solar cell with ZnO nanorods prepared at reactant concentration of 0.04 M provided the largest interface area between polymer active layer and ZnO, resulting in the highest power conversion efficiency of 0.053 % with short circuit current density of 0.43 mA/cm², open circuit voltage of 0.42 V and fill factor of 29 %.

Abstract: Inverted type bulk heterojunction organic solar cell based on ZnO nanorod arrays have been used to overcome the degradation problem of conjugated polymer and low work function electrode. ZnO nanorods and Eosin-Y are widely used to increase the charge mobility and light absorbance, respectively. The effects of Eosin-Y coating temperature (30 – 50 oC) on the performance of organic solar cells based on a blend of poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene] (MEHPPV) as donor and (6,6)-phenyl-C61 butyric acid methyl ester (PC61BM) as acceptor with a structure of fluorine-doped tin oxide (FTO)/Eosin-Y coated ZnO nanorod arrays/MEHPPV:PCBM/Ag were investigated. By using FTO as a substrate, sol-gel and spin coating method was used to deposit ZnO seed layer on FTO surface. The ZnO nanorods were then grown on the ZnO seed layer by chemical bath deposition method and coated with dye by immersing the substrates into Eosin-Y solution at different temperatures. The result shows that absorption of Eosin-Y coated ZnO nanorods increased with dye coating temperature. The optimum power conversion efficiency of η = 1.24 × 10-2 % was achieved at dye coating temperature 50 oC under 100 mW/cm2 simulated AM 1.5 G sunlight.

Abstract: Inverted bulk heterojunction organic solar cells based on vertically aligned dye-coated ZnO nanorods arrays were fabricated. The dye, Eosin-Y was wrapped on ZnO nanorods arrays with dye coating concentration ranging from 0.05 mM to 0.3 mM at room temperature for 1 h. The effects of Eosin-Y solution concentration on the performance of inverted bulk heterojunction organic solar cells based on a blend of poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene] (MEHPPV) as donor and (6,6)-phenyl-C61 butyric acid methyl ester (PCBM) as acceptor with a structure of fluorine-doped tin oxide (FTO)/Eosin-Y coated ZnO nanorod arrays/MEHPPV:PCBM/Ag were investigated. Length, diameter and morphology of ZnO nanorods arrays were characterized. The optical properties of the Eosin-Y coated ZnO nanorod arrays were investigated and the organic solar cells were characterized by current–voltage measurements under 100 mW/cm2 simulated AM 1.5 G sunlight. It was found that current density, Jsc increased from 0.00134 mA/ cm2 to 0.0162 mA/ cm2 with increase in concentration of Eosin-Y from 0.05 mM to 0.3 mM. Solar cell with 0.3 mM Eosin-Y gave the highest power conversion efficiency, which is 7.15×10-4 %. Short circuit current density was 0.0162 mA/ cm2 and the corresponding open circuit voltage was 0.17 V.