Ying-Chan Hsu

Dipolar compounds containing fluorene and a heteroaromatic ring as the conjugating bridge for high-performance dye-sensitized solar cells.

A novel series of dipolar organic dyes containing diarylamine as the electron donor, 2-cyanoacrylic acid as the electron acceptor, and fluorene and a heteroaromatic ring as the conjugating bridge have been developed and characterized. These metal-free dyes exhibited very high molar extinction coefficients in the electronic absorption spectra and have been successfully fabricated as efficient nanocrystalline TiO(2) dye-sensitized solar cells (DSSCs). The solar-energy-to-electricity conversion efficiencies of DSSCs ranged from 4.92 to 6.88%, which reached 68-96% of a standard device of N719 fabricated and measured under the same conditions. With a TiO(2) film thickness of 6 microm, DSSCs based on these dyes had photocurrents surpassing that of the N719-based device. DFT computation results on these dyes also provide detailed structural information in connection with their high cell performance.

1‐Alkyl‐1H‐imidazole‐Based Dipolar Organic Compounds for Dye‐Sensitized Solar Cells

A series of donor-pi-acceptor-type organic dyes based on 1-alkyl-1H-imidazole spacers 1-5 have been developed and characterized. The two electron donors are at positions 4 and 5 of the imidazole, while the electron-accepting cyanoacrylic acid is incorporated at position 2 by a spacer-containing heteroaromatic rings, such as thiophene and thiazole. Detailed investigation on the relationship between the structure, spectral and electrochemical properties, and performance of DSSC is described here. Dye-sensitized solar cells (DSSCs) using dyes as the sensitizers exhibit good efficiencies, ranging from 3.06 to 6.35 %, which reached 42-87 % with respect to that of N719-based device (7.33 %) fabricated and measured under similar conditions. Time-dependent density functional theory (TDDFT) calculations have been performed on the dyes, and the results show that both electron donors can contribute to electron injection upon photo-excitation, either directly or indirectly by internal conversion to the lowest excited state.

Organic dyes containing thienylfluorene conjugation for solar cells

New organic dyes that contain variable lengths of conjugation featuring alternating thiophene and fluorene segments have been synthesized and efficient nano-crystalline TiO2 based dye-sensitized solar cells were fabricated using these molecules as light-harvesting sensitizers.

Dibenzo[f,h]thieno[3,4-b] quinoxaline-based small molecules for efficient bulk-heterojunction solar cells.

Two isomeric compounds (1 and 2) containing a dibenzo[f,h]thieno[3,4-b]quinoxaline core and two peripheral arylamines were synthesized. Solution-processed bulk heterojunction (BHJ) solar cells based on these sensitizers and [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) are reported. The cell fabricated from 1/67 wt % of PCBM exhibited a high power conversion efficiency of 1.70% and an external quantum yield of 55%. The film of the cell was found to have balanced electron and hole mobility and good film morphology.

Dihydrophenanthrene-based metal-free dyes for highly efficient cosensitized solar cells.

Metal-free dyes (BP-1 to BP-3) containing a 9,10-dihydrophenanthrene unit in the spacer have been synthesized. The dye with the highest cell efficiency, BP-2, was used in combination with SQ2 for cosensitized DSSCs. The cosensitized DSSC in which the ratio of BP-2 and SQ2 is 8:2 (v/v) has a record high efficiency of 8.14% among cosensitized systems using all metal-free sensitizers. Dye distribution along the TiO2 film depth was analyzed by an Auger electron spectroscopy technique.

Enhanced light-harvesting capability by phenothiazine in ruthenium sensitizers with superior photovoltaic performance

This paper reports on the design and synthesis of two new ruthenium dyes [Ru(dcbpy)(potip)(NCS)2] (JF-3, dcbpy = 4,4′-dicarboxylic acid-2,2′-bipyridine, potip = 2-(4-(10H-phenothiazin-10-yl)-5-octylthiophen-2-yl)-1H-imidazo[4,5-f][1,10]phenanthroline, and [Ru(dcbpy)(dpotip)(NCS)2] (JF-4, dpotip = 2-(4-(N,N-diphenylamino)-5-octylthiophen-2-yl)-1H-imidazo[4,5-f][1,10]phenanthroline) that contain electron-donating phenothiazine-based or N,N-diphenylamino-based ancillary ligands. The ruthenium dye JF-3, in which an excellent electron-donating phenothiazine is incorporated, shows superior DSC performance (9.1%; compared to 8.8% for N3). A comparison of the electron-donating phenothiazine and N,N-diphenylamino groups utilized in the molecular architecture of ruthenium dyes demonstrates that the phenothiazine group efficiently increases the molar extinction coefficient of band II and also broadens that band in the UV-vis absorption spectrum, reduces device resistance, increases electron lifetime, and enhances power-conversion efficiency. This finding not only clarifies the significance of multifunctionalized design in the molecular architecture of ruthenium dyes, but also represents an alternative route for the introduction of an excellent electron-donating group for improving the light-harvesting characteristics of ruthenium dyes as well as DSC performance.

Magnetization reversal process of ferromagnetic granular thin films probed by magnetization-induced second harmonic generation

We propose to use magnetization-induced second harmonic generation (MSHG) technique to explore the magnetization reversal process of cobalt granular thin films. The three-dimensional magnetization reversal process can be visualized by analyzing the polarization dependent MSHG hysteresis curves. It is found that the magnetization reversal process involves not only the in-plane but also the out-plane magnetization rotation because of the uniaxial anisotropy of cobalt granular thin films. This study demonstrates that MSHG can be a versatile optical technique to investigate the magnetic property of not only ferromagnetic epitaxial thin films but also ferromagnetic granular thin films.

Magnetization-induced second-harmonic generation of cobalt and cobalt oxide nanoparticles

Magnetization-induced second-harmonic generation (MSHG) technique in transverse Kerr configuration is used to explore the nonlinear magneto-optical properties of cobalt and cobalt oxide nanoparticles at room temperature. The nanoparticles are deposited on Si (100) substrate by a RF magnetron sputtering system at room temperature. The STM image of the studied sample indicates that the cobalt particle size is in the range of 10 nm to 30 nm. MSHG technique investigates their magnetic anisotropy property and determines their crystal and magnetic symmetry. The pure cobalt nanoparticle thin films have a large nonlinear Kerr rotation response with a low external magnetic field. The increase of coercivity field, Hc, in the cobalt oxide nanoparticle thin films, can be attributed to the strong interaction between the ferromagnetic cobalt and anti-ferromagnetic cobalt oxide interface. It is found that the magnetic anisotropy is due to the shape anisotropy of cobalt nanoparticle thin film and their interaction. The magnetization reversal process of cobalt nanoparticles involves the rotation of the magnetic moment in the surface plane but not the surface normal plane. This study aims to reveal the important information regarding the magnetization orientation in the ferromagnetic materials and their heterostructures.