Chung-Yen Li

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.

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.

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.

Remarkable effects of primary amide substitution in the sensitizer: an efficient route to enhance the photocurrent density of the solar cell

The incorporation of electron-withdrawing groups in carbene based ruthenium complexes significantly affected their light-harvesting capabilities. The remarkable increase in the conversion efficiency was exhibited by the primary amide substituted sensitizer, CI103 (9.32%), compared to that of CI101 (5.44%) and the N719 dye (8.43%). The finding gives an efficient approach to enhance the photocurrent density and the power conversion efficiency of the solar cell.

A highly conjugated benzimidazole carbene-based ruthenium sensitizer for dye-sensitized solar cells.

A new type of carbene-based ruthenium sensitizer, CB104, with a highly conjugated ancillary ligand, diphenylvinylthiophene-substituted benzimidazolepyridine, was designed and developed for dye-sensitized solar cell applications. The influence of the thiophene antenna on the performance of the cell anchored with CB104 was investigated. Compared with the dye CBTR, the conjugated thiophene in the ancillary ligand of CB104 enhanced the molar extinction coefficient of the intraligand π-π* transition and the intensity of the lower energy metal-to-ligand charge-transfer band. However, the incident photon-to-current conversion efficiency spectrum of the cell anchored with CB104 (0.15 mM) showed a maximum of 63 % at 420 nm. The cell sensitized with the dye CB104 attained a power conversion efficiency of 7.30 %, which was lower than that of the cell with nonconjugated sensitizer CBTR (8.92 %) under the same fabrication conditions. The variation in the performance of these two dyes demonstrated that elongating the conjugated light-harvesting antenna resulted in the reduction of short-circuit photocurrent density, which might have been due to the aggregation of dye molecules. In the presence of a coabsorbate, chenodeoxycholic acid, the CB104-sensitized cell exhibited an enhanced photocurrent density and achieved a photovoltaic efficiency of 8.36 %.

Preparation and Optimization of Iridium Complexes with Quinazolinone Ligands on Solid Supports

Solid-phase combinatorial techniques are tremendously useful in the search for new drugs for the treatment of a wide variety of ailments. Materials discovery, however, has yet to benefit significantly from combinatorial methodology. Indeed, only a few exceptional attempts have been made to apply combinatorial approaches to the discovery of materials possessing novel photophysical properties. Moreover, even among these few reports, most of the materials prepared have been organic compounds. Several researchers have reported the immobilization of organometallic complexes onto functionalized polymer supports. Leadbeater attached ruthenium complexes to polymer supports to improve their catalytic efficiencies; Reedijk and coworkers developed methodologies to prepare platinum complexes on solid supports. Nevertheless, it remains rare for solid-phase combinatorial methods to be used for the synthesis of organometallic materials. In this paper, we describe a rapid and efficient parallel solid phase method for the synthesis of iridium complexes. This methodology allows the modification of three different functionalities on the template of the iridium complexes to optimize and finetune their photophysical properties for application in organic light-emitting diodes (OLEDs). OLEDs are advanced alternatives to inorganic lightemitting diodes and liquid-crystal displays. Because of their excellent properties (flexibility, self-luminescence, rapid response, good contrast, low energy consumption), they hold great potential for application in flat-panel displays. In recent decades, much attention has been focused on organometallic complexes of various heavy metals, including Ir, Os, Ru, and Pt, for their potential use as phosphorescent dopants in OLEDs. Iridium complexes, in particular, are excellent emitters for OLED applications. In 2006, we used a combinatorial organometallic solid phase synthesis and high throughput screening methodology to identify a novel iridium complex having two cyclometallating ligands and a single monoanionic, bidentate ancillary ligand. The optimization of lead organometallic materials using this library approach, however, remains in its nascent stages. As part of a continuing effort toward the development of organometallic materials exhibiting desired properties, we are aiming to optimize the properties of organometallic complexes through structural modifications using solid phase synthesis. So far, the key ligands we have used have been limited mostly to derivatives of o-pyridylarenes and o-pyridylheterocycles. Therefore, to extend our optimization studies, for this present study we selected iridium complexes featuring quinazolinone-based cyclometallating ligands. In this Report, we demonstrate the versatility of using a combinatorial parallel approach, applying solid phase synthesis, for the preparation and optimization of iridium complexes incorporating quinazolinone ligands as luminescent emitters. The parallel solid-phase syntheses of the iridium complexes 1 were carried out using Wang resin (1% DVB, 1.0 mmol/g, Scheme 1). Initially, Mitsunobu alkylation was tested to obtain resin 2 by reacting methyl 4-hydroxybenzoate with Wang resin under standard conditions. In these cases, the reactions afforded poor yields and resulted in several side products. Instead, we first activated the Wang resin as a mesylate and then alkylated it with methyl 4-hydroxybenzoate in DMF using NaH to afford the resin 2 * Towhomcorrespondenceshouldbeaddressed.E-mail:ch01@ncu.edu.tw. Fax: +886-3-427-7972.  Copyright 2009 by the American Chemical Society