Elsevier

Solar Energy

Volume 85, Issue 6, June 2011, Pages 1189-1194
Solar Energy

Stable dye-sensitized solar cells based on organic chromophores and ionic liquid electrolyte

https://doi.org/10.1016/j.solener.2011.02.025Get rights and content

Abstract

A series of polyene–diphenylaniline based organic dyes (coded as D5, D7, D9 and D11) have been reported for the application in ionic liquid electrolyte based dye-sensitized solar cells. The effects of substitution of organic dyes on the photovoltaic performance have been investigated, which show addition of methoxy groups on the triphenylamine donor group increases short-circuit current, open-circuit voltage and photovoltaic performance. A power conversion efficiency of 6.5% under AM 1.5 sunlight at 100 mW/cm2 has been obtained with D11 dye in combination with a binary ionic liquid electrolyte, which when subjected to accelerated testing under one sun light soaking at 60 °C, the efficiency remained 90% of initial efficiency.

Highlights

► Dye-sensitized solar cells based on Polyene–diphenylaniline organic sensitizers explored. ► Alkoxy group substitution on the triphenylamine donor increases the photovoltaic performance. ► DSC devices with Ionic liquid electrolytes exhibit good stability.

Introduction

Renewable energy has recently attracted massive attention because of dwindling of traditional fossil energy, and high price. In this respect, solar energy is inexhaustible; about 3 × 1024 J can be supplied to the Earth from the Sun per year, or about 10,000 times more than the global population currently consumes (Grätzel, 2001, O’Regan and Gratzel, 1991). Among the several technologies for converting solar energy into electricity mesoscopic dye-sensitized solar cells (DSCs) have attracted intense interest owing to cheap, and efficient (Grätzel, 2001, Wang et al., 2003, O’Regan and Gratzel, 1991, Gratzel, 2005). Since the first report of dye-sensitized solar cell in 1991, significant progress has been made through the development of photoanode materials, sensitizers, and electrolytes. The sensitizer is a crucial element in DSCs, exerting significant influence on the power conversion efficiency as well as the stability of the devices. A series of high-molar-extinction-coefficient ruthenium complexes containing π-conjugated ligand systems have been successfully introduced showing excellent photovoltaic performance and stability (Chen et al., 2006, Chen et al., 2007, Chen et al., 2008a, Chen et al., 2008b, Chen et al., 2009, Karthikeyan et al., 2007, Kroeze et al., 2006, Gao et al., 2008a, Gao et al., 2008b, Shi et al., 2008, Abbotto et al., 2008, Kuang et al., 2007a, Kuang et al., 2007b, Wang et al., 2005, Yu et al., 2010).

It is known that increase in the molar extinction coefficient and panchromatic response of the sensitizer can improve the solar cell performance. Metal-free organic dyes normally show higher molar extinction coefficients compared to the metal complexes. Further, they are environmentally friendly, easy to synthesize and cheap. Even though efficiencies are closer to 10% have been reached with metal free organic dyes, there is still a need to optimize their chemical and physical properties for further improvement of the device performance (Xu et al., 2009, Zang et al., 2009, Wang et al., 2008, Shi et al., 2008, Kim et al., 2008a, Kim et al., 2008b, Choi et al., 2008a, Choi et al., 2008b, Cid et al., 2007a, Cid et al., 2007b, Yum et al., 2007, Ferrere et al., 1997, Ferrere and Gregg, 2002, Tian et al., 2000, Ito et al., 2006, Zhang et al., 2009, Zeng et al., 2010, Mishra et al., 2009).

Ionic liquids (ILs) represent a new and attractive class of solvent free electrolytes, which are appealing due to their negligible vapor pressure under photovoltaic operating conditions as well as their high conductivity and thermal stability (Welton, 1999, Rogers et al., 2003, Wasserscheid and Welton, 2003, Dyson, 2002, Xue and Shreeve, 2005, Zhao et al., 2005). A number of ILs have already been examined for DSCs (Kuang et al., 2006, Kubo et al., 2002, Kawano et al., 2004, Matsumoto et al., 2001, Wang et al., 2005, Mazille et al., 2006, Fei et al., 2006, Zakeeruddin and Grätzel, 2009, Kuang et al., 2007b, Bai et al., 2008, Wang et al., 2004, Zakeeruddin and Grätzel, 2009). Here we report detailed photovoltaic performance investigations based on a series of polyene–diphenylaniline based dyes and ionic liquid electrolyte resulting a power conversion efficiency of 6.5% under AM 1.5 sunlight at 100 mW/cm2, which shows excellent stability behavior after long-term accelerated tests under one sun light illumination at 60 °C. Electrochemical impedance and photovoltage transient studies reveal the pivotal influence exerted by the chemical structure of the polyene–diphenylaniline based organic dyes on the photovoltaic performance of the device.

Section snippets

Results and discussion

Fig. 1 shows molecular structures of the four new dyes, which were synthesized using previously reported synthetic routes (Hagberg et al., 2008, Hagberg et al., 2006, Qin et al., 2007). The structure of D5 sensitizer was modified with the addition diphenylaniline and methoxy groups which named as D7, D9, D11 dyes. The molar extinction coefficients of the D5, D7, D9 and D11 dyes are 33,000 M−1 cm−1 (441 nm), 31,000 M−1 cm−1 (441 nm), 33,000 M−1 cm−1 (464 nm) and 38,000 M−1 cm−1 (458 nm), respectively.

Fig. 2

Reagents

The four polyene–diphenylaniline based organic dyes were synthesized according to previous procedure (Hagberg et al., 2008, Hagberg et al., 2006, Qin et al., 2007) and 1-butyl-1H-benzimidazole (NBB) were synthesized as reported earlier (Abbotto et al., 2008). The ILs 1-propyl-3-methylimidazolium iodide (PMII) was synthesized according to the literature methods and the purity was confirmed by 1H NMR analysis. Guanidinium thiocyanate (GuNCS) and 1-ethyl-3-methyl-imidazolium tetracyanoborate

Acknowledgment

We acknowledge the financial support of this work by the Swiss Swiss National Science Foundation, Swedish Research Council, Swedish Energy Agency and the Knut and Alice Wallenberg foundation for financial support. MKN thanks the World Class University (WCU) program funded by the Ministry of Education, Science and Technology (Grant No. R31-2009-000-10035-0).

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    Present address: School of Chemistry and Chemical Engineering, Sun Yat-Sen University, Guangzhou, Guangdong 510275, China.

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