Chaochin Su

Carbene-based ruthenium photosensitizers

A new series of N-heterocyclic carbene (NHC)-pyridine ruthenium complexes incorporating a carbene unit as an ancillary ligand were designed and successfully synthesized by using simple synthetic methods. The photophysical, electrochemical and photovoltaic properties of these NHC-pyridine based ruthenium complexes were investigated. These complexes showed photoelectric conversion efficiencies in the range of 6.43 ∼ 7.24% under the illumination of AM 1.5 (100 mW cm(-2)). Interestingly, the modifications on the ancillary ligand of these sensitizers by removal of an alkoxyl group and replacement of the octyl chain with a 3,5-difluorobenzyl group showed a 13% increase in the conversion efficiency for the CifPR dye. These results demonstrated that structural modifications on the NHC-pyridine ancillary ligand of ruthenium complexes results in dye-sensitized solar cells exhibiting a comparable cell performance to that obtained using the standard N719 dye.

New Pyridinium Ylide Dyes for Dye Sensitized Solar Cell Applications

Novel organic pyridinium ylide sensitizers (NO109-111) consisting of various anchoring groups were synthesized and characterized for applications in dye sensitized solar cells. Compared with the pyridine-N-oxide dye (NO108), the ylide sensitizers with strong electron-withdrawing acceptors exhibited dominant ultraviolet absorption properties and efficient binding abilities to the TiO2 surface. Among these dyes, the pyridinium ylide NO111 sensitized solar cell showed the highest efficiency (5.15%), which was improved to 7.41% by employing coadsorbent chenodeoxycholic acid.

Novel oxindole based sensitizers: synthesis and application in dye-sensitized solar cells.

Two novel oxindole sensitizers have been synthesized for dye-sensitized solar cell applications. These new dyes can provide an additional pathway to inject electrons into the photoanode through the partial chelation of their amide carbonyl groups to the TiO2 surface. Incorporation of an electron deficient pyridine in the acceptor of the TI125 dye was found to enhance the photovoltage and conversion efficiency of the cell.

Effect of copper oxide oxidation state on the polymer-based solar cell buffer layers.

Transporting buffer layers are important components of polymer-based organic photovoltaic devices. In this study, we have investigated the effects of the oxidation state in copper oxide based buffer layer in conjunction to its role in device performance. We have shown that variation in the oxidation state affects the band alignment and built-in voltage of the device, therefore leading to variation in device performance. Specifically, the fully oxidized copper oxide buffer layer has a valence band position at 5.12 eV, much closer to the highest occupied molecular orbital of poly(3-hexylthiophene-2,5-diyl) (P3HT) (∼5.2 eV), giving a best fill factor and efficiency at 57% and 4.06%, respectively. Lastly, we also demonstrate significant enhancement in device stability, with power conversion efficiency maintained at 75% of the original value even after 40 days, and propose a strategy for recovering the device performance based on the observed property of the oxide buffer layer.

Preparation and characterization of pure rutile TiO 2 nanoparticles for photocatalytic study and thin films for dye-sensitized solar cells

Pure rutile-phase TiO2 (r-TiO2) was synthesized by a simple one pot experiment under hydrothermal condition using titanium (IV) n-butoxide as a Ti-precursor and HCl as a peptizer. The TiO2 products were characterized by XRD, TEM, ESCA, and BET surface area measurement. The r-TiO2 were rodlike in shape with average size of ∼61 × 32nm at hydrothermal temperature of 220°C for 10 h. Hydrothermal treatment at longer reaction time increased the tendency of crystal growth and also decreased the BET surface area. The degradation of methylene blue was selected as a test reaction to confer the photocatalytic activity of as-obtained r-TiO2. The results showed a strong correlation between the structure evolution, particle size, and photocatalytic performance of r-TiO2. Furthermore, the r-TiO2-based solar cell was prepared for the photovoltaic characteristics study, and the best efficiency of ∼3.16% was obtained.

Preparation of smooth surface TiO 2 photoanode for high energy conversion efficiency in dye-sensitized solar cells

Dye-sensitized solar cells (DSSCs) based on a TiO2 photoanode have been considered as an alternative source in the field of renewable energy resources. In DSSCs, photoanode plays a key role to achieve excellent photo-to-electric conversion efficiency. The surface morphology, surface area, TiO2 crystal phase, and the dispersion of TiO2 nanoparticles are the most important factors influencing the properties of a photoanode. The smooth TiO2 surface morphology of the photoanode indicates closely packed arrangement of TiO2 particles which enhance the light harvesting efficiency of the cell. In this paper, a smooth TiO2 photoanode has been successfully prepared using a well-dispersed anatase TiO2 nanosol via a simple hydrothermal process. The above TiO2 photoanode was then compared with the photoanode made from commercial TiO2 nanoparticle pastes. The morphological and structural analyses of both the aforementioned photoanodes were comprehensively characterized by scanning electron microscopy and X-ray diffraction analysis. The DSSC fabricated by using a-TiO2 nanosol-based photoelectrode exhibited an overall light conversion efficiency of 7.20% and a short-circuit current density of 13.34mA cm-2, which was significantly higher than those of the DSSCs with the TiO2 nanoparticles-based electrodes.

Enhancing efficiency with fluorinated interlayers in small molecule organic solar cells

This study presents a simple approach to improve the performance of small molecule based organic solar cells (OSCs) by inserting a fluorinated buffer layer (e.g., PFAS) at the hetero-interface of bilayer devices. As demonstrated in this work, the PFAS modification reduces the surface energy of the conventional PEDOT : PSS photoanode and results in a significant improvement in the pentacene based OSC. The passivated PEDOT : PSS surface after PFAS modification has a lower interface energy with pentacene and facilitates 3D single crystalline (dendritic-like) phase pentacene growth. Concurrently, the accumulated negative charges of the fluorinated PFAS layer result in the development of interfacial dipole moments that in turn lead to an enhanced built-in potential across the devices, and consequently enhanced hole transport efficiency. Improved performance of the modified OSCs is evident from the ∼97% enhancement in efficiency from 0.88% to 1.73%, along with the open-circuit voltage improvement from 0.29 to 0.42 V. As well as improving the photovoltaic performance, the PFAS treatment also enhances the stability of the device under high temperature annealing, which is essential in the fabrication process.

Preparation of Nanoporous TiO2 Electrodes for Dye-Sensitized Solar Cells

Nano-porous thin films have been widely used as the working electrodes in dye-sensitized solar cells (DSSCs). In this work, the phase-pure anatase (a-) and rutile (r-) have been prepared using hydrothermal processes. The investigation of photo-to-electron conversion efficiency of DSSCs fabricated from mixed- with a- and r- ratio of 80 : 20 (A8R2) was performed and compared to that from commercial (DP-25). The results showed higher efficiency of DSSC for A8R2 cells with same dependence of cell efficiency on the film thickness for both A8R2 and DP-25 cells. The best efficiency obtained in this work is 5.2% from A8R2 cell with film thickness of 12.0 . The correlation between the films thickness and photoelectron chemical properties of DSSCs fabricated from A8R2 and DP-25 was compared and discussed.

Preparation, characterization, and application of titanium nano-tube array in dye-sensitized solar cells

The vertically orientated TiO2 nanotube array (TNA) decorated with TiO2 nano-particles was successfully fabricated by electrochemically anodizing titanium (Ti) foils followed by Ti-precursor post-treatment and annealing process. The TNA morphology characterized by SEM and TEM was found to be filled with TiO2 nano-particles interior and exterior of the TiO2 nano-tubes after titanium (IV) n-butoxide (TnB) treatment, whereas TiO2 nano-particles were only found inside of TiO2 nano-tubes upon titanium tetrachloride (TiCl4) treatment. The efficiency in TNA-based DSSCs was improved by both TnB and TiCl4 treatment presumably due to the increase of dye adsorption.

Process development and photocatalytic property of nanofluid prepared by combined ASNSS

Abstract This study proposes a new method: the combined arc-submerged nanoparticle synthesis system (ASNSS) for preparing TiO2 nanofluid. In addition to the influence of the various process variables such as breakdown voltage, peak current and dielectric liquid temperature on nanoparticles, this study will also discuss the photocatalytic activity of the prepared TiO2 nanoparticle suspension. To examine the photocatalytic activity of the TiO2, the photodecomposition of salicylic acid was carried out. Experimental results show that the proposed method can successfully prepare anatase TiO2 and this nanofluid can be stabilised for longer than six months. The rate constant of photocatalytic reaction of TiO2 nanoparticles for salicylic acid is 0·0035. Experimental results indicate that the TiO2 nanoparticle fluid possesses excellent photocatalytic activity in photodegradation of salicylic acid.