Cosensitization of Ruthenium–Polypyridyl Dyes with Organic Dyes in Dye-sensitized Solar Cells

Abstract

Cosensitization, a technique involving sensitization of a metaloxide semiconductor electrode with two or more different dyes, is a promising strategy to enhance light-harvesting capabilities of dye-sensitized solar cells through expansion of the light absorption range. In this review, we introduce recent developments in highly efficient solar cells cosensitized by rutheniumpolypyridyl and organic dyes. Design strategies for cosensitizer molecules, development of UV and NIR cosensitizers, and performances of reported cosensitized solar cells are reviewed. Cosensitization is an effective method to improve the conversion efficiencies, as not only photocurrent but also photovoltage can be increased by employing an appropriate cosensitizer. Ç IntroductionSolar light is anticipated to become a leading nextgeneration clean and sustainable energy resource. An efficient method to convert solar light to useful energy is by using a photoelectric conversion device, namely, solar cells. Currently, Si-based solar cells are being widely used in practical applications. However, because of the limitations of material resources and high production costs, it is important that costeffective alternatives are developed. Since O'Regan and Grätzel reported high conversion efficiency based on a mesoporous TiO 2 and rutheniumbipyridyl dye system, 1 dye-sensitized solar cells (DSCs) have been attracting increasing attention as an alternative to Si-based solar cells because of their low production cost and relatively high photon-to-electricity conversion efficiencies. Many researchers have focused their efforts on improving the photovoltaic properties of DSCs. The DSC device consists of a transparent conducting oxide (TCO) glass substrate, mesoporous TiO 2 electrode, sensitizing dye, counter electrode, and an electrolyte as shown in Figure 1a. The incident light through the TCO glass is absorbed by the dyes present on the TiO 2 surface; the subsequent injection of the photoexcited electrons from the dyes into the TiO 2 conduction band (CB), results in dye oxidation. The injected electrons are transported to the external circuit via TiO 2 and TCO. On the other hand, the oxidized dye is regenerated by I ¹ in the electrolyte, and the oxidized I 3 ¹ ion is then recovered at the counter electrode. Among the components of the DSC device, the nature of the dye is key in regulating its light-harvesting capability, electron injection efficiency, and oxidized dye regeneration rates.The conversion efficiency of solar cells (©) is calculated by eq 1.where J sc is the short circuit current density, V oc is the open circuit voltage, FF corresponds to fill factor, and I o is the incident light energy. Therefore, in order to improve the photovoltaic properties of the solar cells, J sc , V oc , and FF have

Merging Biology and Photovoltaics: How Nature Helps Sun‐Catching

“…In short, the design of dyes for highly performing DSSCs should fulfill several requirements: i) high molar extinction coefficient, ii) broadband absorption spectra covering visible and Near-IR range, iii) strong binding or electron coupling with the mesoporous semiconductor, iv) alignment of energy levels, with regard to the conduction band of the semiconductor and the redox couple potential, and v) stability upon continuous sunlight exposition. [163,164] Along these lines, sustainable and/or bio-based dyes include proteins and natural dyes. [165][166][167] Their device performance, implementation and limitations will be summarized in Section 5.3.…”

Fabrication of a high-performance dye-sensitized solar cell with 12.8% conversion efficiency using organic silyl-anchor dyes

“…4 Besides the high photovoltaic performance, the TiO 2 photoelectrode sensitized with ADEKA-1 possesses much higher durability to mixed solvents containing nitrile and water than those with conventional carboxy-anchor dyes. In DSSCs co-sensitization by using two kinds of dyes has been demonstrated to be effective to improve the energy conversion efficiencies, [6][7][8][9][10][11] and the durability of the photoelectrode allows co-adsorption of plural sensitizing dyes to the electrode for producing the co-sensitization effect.…”

Terpyridine-Containing π-Conjugated Polymers for Light-Emitting and Photovoltaic Materials

“…One of the key ways to achieve this is by improving the spectral match between solar light and organic sensitizing materials. Since ruthenium complexes exhibit reversible Ru(II)/Ru(III) redox processes and MLCT transitions in the range 500–600 nm, organic materials based on ruthenium polypyridine complexes are widely used in OPVs (Zakeeruddin et al, 2002 ; Numata et al, 2013 ). Cheng et al ( 2008 ) firstly reported synthesis and photovoltaic performances of the metallo-polymers based on tpy units.…”