Yung-Sheng Yen

Recent developments in molecule-based organic materials for dye-sensitized solar cells

Photoanodes such as TiO2, sensitizers, electrolytes, and photocathodes play important roles in dye-sensitized solar cells (DSSCs). Organic materials are often used for these components. This feature article reviews the recent development of organic sensitizers for both n- and p-type DSSCs, with an emphasis on molecular design strategies. This paper also discusses dyes for co-sensitized and tandem DSSCs, and metal-containing and metal-free redox organic mediators. Finally this paper briefly discusses organic materials for counter electrodes. The article provides readers with an overview of new trends in organic materials for DSSCs.

2,6-Conjugated anthracene sensitizers for high-performance dye-sensitized solar cells

Metal-free dyes (Ant1 to Ant4) containing a 2,6-conjugated anthracene unit in the spacer have been synthesized. The conversion efficiency (7.52%) of the dye-sensitized solar cell using Ant3 as the sensitizer reached ∼90% of the standard N719-based cell (8.41%). The co-sensitized DSSC using Ant3 and a near-IR dye (SQ2) exhibited an improved efficiency of 8.08%. With addition of a co-adsorbent, CDCA, the cell efficiency (9.11%) of the Ant3-based DSSC surpassed that of the N719-based standard cell. An even higher efficiency of 10.42% was achieved under weak light irradiation.

Benzotriazole-Containing D–π–A Conjugated Organic Dyes for Dye-Sensitized Solar Cells

A series of metal-free benzotriazole-based dipolar dyes have been developed as sensitizers for dye-sensitized solar cells (DSSCs). Different heteroaromatic rings such as furan, thiophene, and selenophene, were used in combination with benzotriazole as the conjugated spacer group. Light harvesting, charge recombination, and electron injection of the cells fabricated are affected by the heteroaromatic ring used in the spacer. The DSSC with the thiophene-containing dye has the highest conversion efficiency of 6.20%, which reaches 85% of the standard cell based on N719.

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.