Ruri Agung Wahyuono

Aqueous Photocurrent Measurements Correlated to Ultrafast Electron Transfer Dynamics at Ruthenium Tris Diimine Sensitized NiO Photocathodes

Understanding the structural and electronic factors governing the efficiency of dye-sensitized NiO photocathodes is essential to optimize solar fuel production in photoelectrochemical cells (PECs). For these purpose, three different ruthenium dyes, bearing either two or four methylphosphonate anchoring groups and either a bipyridine or a dipyridophenazine ancillary ligand, were synthesized and grafted onto NiO films. These photoelectrodes were fully characterized by XPS, ToF-SIMS, UV-vis absorption, time-resolved emission and femtosecond transient absorption spectroscopies. Increasing the number of anchoring groups from two to four proved beneficial for the grafting efficiency. No significant modification of the electronic properties compared to the parent photosensitizer was observed, in accordance with the non-conjugated nature of the grafted linker. The photoelectrochemical activity of the dye-sensitized NiO electrodes was assessed in fully aqueous medium in the presence of an irreversible electron acceptor and photocurrents reaching 190 μA.cm-2 were recorded. The transient absorption study revealed the presence of two charge recombination pathways for each of the sensitizers and evidenced a stabilized charge separated state in the dppz derivative, supporting its superior photoelectrochemical activity.

Photoelectrochemical performance of DSSC with monodisperse and polydisperse ZnO SPs

Zinc oxide, ZnO, is one of oxide semiconductors being used in DSSC. ZnO is promising material for having fairly higher energy band gap and much higher bulk electron mobility than that of anatase TiO2, the most widely used semiconductor for DSSC photoelectrode. This study introduces the synthesis of ZnO by precipitation method. The synthesis involves ZnAc dihydrate and diethylene glycol (DEG) for the chemicals. Various size of ZnO spherical particles (SPs) are obtained in polydisperse and monodisperse particles. Monolayer and bilayer DSSCs are fabricated in sandwich structure and sensitized with N719 dye for 3 and 5 hours. Monolayer DSSC using monodisperse particles (422 nm) is able to generate highest conversion efficiency of 0.569% (Voc = 541.3 mV, Jsc = 1.92 mA/cm2, and fill factor of 54.78%). Bilayer DSSC, i.e. combined 422 - 185 nm ZnO layer, can optimize the photocurrent action spectra in UV regime leading to high conversion efficiency of 0.568 (Voc = 568.2 mV, Jsc = 2.22 mA/cm2, and fill factor of 4...

ZnO nanoflowers-based photoanodes: aqueous chemical synthesis, microstructure and optical properties

Abstract We have developed an efficient, low temperature, synthetic route for ZnO nanoflowers (NFs) as photoanode material. This alternative route yields small flowerlike nanostructures, built from densely self-assembled tip-ended rod structures. The obtained ZnO NFs possess a large bandgap of 3.27 - 3.39 eV, enabling the generation of an average open current voltage of 0.56 V. Additionally, they show a high internal light harvesting of 14.6•10-7A-mol-1. The growth mechanism and self-assembly of ZnO NFs were studied in detail by joint spectroscopic-TEM investigations. It is shown that the ZnO crystallite size increases with increasing annealing temperatures and that the stress and the improved crystallinity are induced by annealing and reduce the lattice strain and the dislocation density. The bandgaps of ZnO are affected by the lattice strain revealing an optimal region of lattice strain to gain high bandgap energies. The properties of the synthesized ZnO NFs are compared with other morphologies, i.e. ZnO spherical aggregates (SPs) and ZnO nanorods (NRs), and are tested as electrode materials in dye-sensitized solar cells.

Modeling and experiment of dye-sensitized solar cell with vertically aligned ZnO nanorods through chemical bath deposition

A theoretical model based on electron diffusion differential equation and Schottky barrier model was developed to determine the current–voltage characteristics of DSSC. To verify the model DSSC with ZnO nanorods photoelectrode which was chemically bath deposited onto the TCO was fabricated. According to modeling results, increasing of recombination current density J at these interfaces results in a decrease in Schottky barrier height φb and therefore improves the photovoltage under the open-circuit condition. It is found that the open-circuit voltage remains constant when the TCO/ZnO Schottky barrier height was varied in the range of 0.45 – 0.6 eV. This theoretical model consistents with the experimental result in which the fabricated DSSCs can produce conversion efficiency in the range of 0.98 – 1.16%. The trend in photovoltage calculated in the theoretical model basically agrees with the experimental result, although the calculated photocurrent is somewhat over estimated compared to the experimental results. The model presents that the ideality factor for ZnO nanorods, which also contributes to the enhancement of photovoltage, increases in the range of 2.75 – 3.0 as the annealing temperature is increased in the experiment.

Integrated ZnO nanoparticles on paper-based microfluidic: toward efficient analytical device for glucose detection based on impedance and FTIR measurement

Microfluidic paper-based analytical devices decorated with ZnO nanospherical (nanoSPs) aggregates (ZnO-μPAD) for glucose detection have been fabricated. ZnO nanoSPs were prepared by wet chemical synthesis and integrated on the optimized geometry of ZnO-μPAD has 0.2 and 0.4 mm of channel width and length, respectively. Glucose detection measurements were based on electrochemical and infrared transmission measurements. The glucose concentrations were adjusted as 5, 6.5, and 9 mmol, i.e. typical glucose level for normal, pre-diabetes and diabetes, in a mixture of ringer lactate as simulated biological fluid and red blood cells. ZnO nanoSPs in this study possess an average aggregate size of 160 nm formed by clustered ~ 18 nm crystallite size and ordered porous matrix as well as a surface area of 15 m2·g-1.The separation process of the glucose sample on ZnO-μPAD requires approximately 45 s. The glucose detection results show that both electrochemical-based and FTIR-based measurements perform a linear measurement system (R2 of 0.81 to 0.99) with a relatively high sensitivity. A linearly decreasing impedance spanning from 2.2 – 0.6 Ohm and linearly increasing ΔIR transmission spanning from 3 – 19% are obtained for glucose level ranging from 5 – 9 mmol.

The Effect of Paste Preparation and Annealing Temperature of ZnO Photoelectrode to Dye-Sensitized Solar Cells (DSSC) Performance

Dye-sensitized Solar Cells (DSSCs) have been successfully fabricated by using ZnO nanoparticles (NPs). The ZnO photoelectrode was prepared by using pastes solved in water-based and ethanol-based solvent. The ZnO NPs was synthesized by copresipitation method, prepared by reaction from Zinc Acetate with diethylene glycol (DEG). The obtained ZnO NPs has 13.93 nm particle diameter. Scanning Electron Microscopy (SEM) showed that ZnO NPs from monodisperse spherical aggregate with particle diameter of approximately 300nm. The band gap was found of 3.29eV. Variations of annealing temperature were carried out in photo-electrode fabrication. This work employs extracts from mangosteen pericarp as natural dye for fabrication of DSSCs. DSSCs were fabricated in sandwich structure with redox couple electrolyte I3-/I- and Pt-catalyst counter electrode. The best efficiency of 0.11% (Voc = 232.4 mV, Jsc = 111.6 µA/cm2, FF = 61.41 %) was obtained for DSSCs using ZnO photo-electrode prepared by ethanol-based paste and 200°C of annealing temperature.

Quasi-Solid State DSSC Performance Enhancement by Bilayer Mesoporous TiO2 Structure Modification

Quasi-solid state dye-sensitized solar cells (DSSC) having bilayer structure were made by using nanocrystalline anatase-rutile TiO2 to enhance the photovoltaic performance. The bilayer structures were coated to FTO glass using doctor blade technique with total active area of 0.4 cm2. Cyanidin dye extracted from mangosteen pericarp was used as photosensitizer. Bilayer anatase-anatase was formed with surface area of 99.9 m2/g and pore volume of 0.23 cc/g while anatase-rutile structure has surface area of 103.5 m2/g and pore volume of 0.21 cc/g. Overall energy conversion efficiencies under illumination of 10 mW/cm2 of 0.461% and 0.1365% were achieved for DSSC employing anatase-anatase and anatase-rutile TiO2 structure, respectively. Both efficiencies were higher than that of monolayer anatase and rutile TiO2 structure whose efficiencies in the range of 0.02% to 0.037%. The photocurrent action spectra of bilayer structures performed high efficiency spectrum in the wavelength range of 420 480 nm owing to cyanidin effect of dye.

Blood plasma separation in ZnO nanoflowers-supported paper based microfluidic for glucose sensing

Blood plasma separation is essential to analyze and quantify the bio-substances in the human blood and hence, allows for diagnosing various diseases. This paper presents the two layer paper-based microfluidic analytical devices coated with ZnO nanoflowers (ZnO NF-µPAD) for a rapid blood plasma separation and glucose sensing. Plasma separation in ZnO NF-µPAD was evaluated experimentally and numerically using computational fluid dynamics package for a flow over porous networks. Glucose detection was carried out using Fourier-transform infrared (FTIR) measurements. The glucose concentrations in the red blood samples investigated here vary in the range of 150 – 310 mg·dl-1. The plasma separation process on ZnO NF-μPAD requires 240 ± 93 s. The spectroscopic data reveals that the IR absorptions and Raman signals at the typical vibrational frequencies of glucose are increasing at higher glucose concentration. After subtraction from absorption background arising from ZnO NF and the paper, linearly increasing IR absorption (913 and 1349 cm-1) and Raman signals (1346 and 1461 cm-1) are observable with a relatively good sensitivity.Blood plasma separation is essential to analyze and quantify the bio-substances in the human blood and hence, allows for diagnosing various diseases. This paper presents the two layer paper-based microfluidic analytical devices coated with ZnO nanoflowers (ZnO NF-µPAD) for a rapid blood plasma separation and glucose sensing. Plasma separation in ZnO NF-µPAD was evaluated experimentally and numerically using computational fluid dynamics package for a flow over porous networks. Glucose detection was carried out using Fourier-transform infrared (FTIR) measurements. The glucose concentrations in the red blood samples investigated here vary in the range of 150 – 310 mg·dl-1. The plasma separation process on ZnO NF-μPAD requires 240 ± 93 s. The spectroscopic data reveals that the IR absorptions and Raman signals at the typical vibrational frequencies of glucose are increasing at higher glucose concentration. After subtraction from absorption background arising from ZnO NF and the paper, linearly increasing IR a...

The Effective Mixture of Anatase–Rutile Nanoparticles as Dye-Sensitized Solar Cell (DSSC) Using Natural Dye of Garcinia mangostana and Rhoeo spathacea Extract

A synergistic effect between anatase and rutile TiO2 is known to be able to improve light harvesting and the overall solar conversion efficiency. Dye-sensitized solar cell (DSSC) was fabricated using the mixture of anatase–rutile phase of TiO2 nanoparticles prepared through co-precipitation method with TiCl3 precursors. The particle’s sizes were 30 nm for anatase and 44.9 nm for rutile as characterized by using XRD (X-ray diffraction). The natural dyes employed were Garcinia mangostana pericarp extract and Rhoeo spathacea extract. The two selected dyes were used because of their abundant availability and good performance for being used as photosensitizer as indicated by their absorbance wavelength of 392.5 nm for G. mangostana extract and 432 and 658 nm for R. spathacea. Both dyes contain anthocyanin pigment, which is a known visible-light trapper that undergoes charge excitation, and upon complexation with a metal oxide semiconductor like TiO2, a charge-transfer process occurs. Our results show that the best performance of DSSC having anatase/rutile ratio of 90:10 (η = 0.076%) and (η = 0.063%) was obtained for samples sensitized with G. mangostana extract and R. spathacea extract, respectively. This ratio has the largest surface area and smallest particle size. The synergistic effect of the two phases is due to the ease of electron migration from rutile to anatase conduction band and larger surface area allowing more dye being able to be absorbed.

Effects of nano anatase-rutile TiO2 volume fraction with natural dye containing anthocyanin on the dye sensitized solar cell performance

Since its first development, efforts to improve efficiency of Dye Sensitized Solar Cell (DSSC) are continuously carried out, either through selection of dye materials, the type of semiconductor, counter electrode design or the sandwiched structure. It is widely known that anatase and rutile are phases of TiO2 that often being used for fabrication of DSSC. Rutile is thermodynamically more stable phase having band-gap suitable for absorption of sunlight spectrum. On the other hand, anatase has higher electrical conductivity, capability to adsorp dye as well as higher electron diffusion coefficient than those of rutile. Present research uses mangosteen pericarp and Rhoeo spathacea extracted in ethanol as natural dye containing anthocyanin. These dyes were characterized by using UV-Vis and FTIR, showing that the absorption maxima peaks obtained at 389 nm and 413 nm, for mangosteen and Rhoeo spathacea, respectively. The nano TiO2 was prepared by means of co-precipitation method. The particle size were 9-11 nm ...