Quasi-solid-state dye-sensitized solar cells with cyanoacrylate as electrolyte matrix

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Abstract

A quasi-solid-state dye-sensitized solar cells (DSSCs) employing a commercial glue (“SuperGlue®”) as electrolyte matrix was fabricated. The cyano groups of the cyanoacrylate can form a supramolecular complex with tetrapropylammonium cations. This immobilizes the cations and therefore might lead to a favored anionic charge transport necessary for a good performance of the iodide/triiodide electrolytic conductor. Obtaining energy conversion efficiencies of more than 4% under 100 mW/cm2 of simulated A.M. 1.5 illumination, the cyanoacrylate quasi-solid-state electrolyte is an ordinary and low-cost compound which has fast drying property and offers significant advantages in the fabrication of solar cells and modules as it is in itself is a very good laminating agent. The influences of different porous layer thicknesses of titanium oxide and various kinds of cations on DSSC performance and long-term stability are presented.

Introduction

Since 1991 [1], dye-sensitized nanocrystalline titanium oxide solar cells (DSSCs) using a liquid electrolyte as ionic conductor have received considerable attention because of their high solar energy conversion efficiencies up to 10% [2] and because of the prospective of a low production costs. However, the liquid electrolyte has some major technological disadvantages as it requires very advanced sealing and breakage protection to avoid leakage or evaporation losses lowering the performance as well as posing a threat to the environment. Therefore, large efforts have been made into replacing the liquid electrolyte by inorganic and organic semiconductors [3], [4], [5], [6] or solid polymer electrolytes [7], [8], [9], [10]. Unfortunately, photoelectrochemical cells based on solid polymer electrolyte have low conversion efficiency compared to the liquid versions, because of the high recombination rate at the TiO2/solid-state-electrolyte interface and the low conductivity of the solid-state-electrolyte itself [11].

An alternative approach to retain the good device properties of the liquid electrolytes while drastically reducing these problems is the use of quasi-solid electrolytic materials. Polymer gel electrolytes can exhibit as high ionic conductivities as liquid electrolytes, and the gelation mitigates the potential instability against solvent leakage. In 2003, 6% solar energy conversion efficiency was reported in quasi-solid-state DSSCs based on poly(vinylidenefluoride-co-hexafluoropropylene (PVDF-HFP) matrix showing stable performance under both thermal stress and light soaking, matching the durability criteria applied to silicon solar cells for outdoor applications [12]. In 2006, Biancardo et al. reported that quasi-solid-state DSSCs based on poly(methyl-methacrylate) (PMMA) polymer matrix were fabricated to be a large area solar module composed of a master plate of 25 cm×25 cm with 23 cells (active area of 12.5 cm2 per cell) connected in series, which allows power extraction up to ∼100 mW with an Isc of 25.1 mA and a Voc of 10.65 V under A.M. 1.5, 100 mW/cm2 standard conditions presenting solar cells application in building elements like windows, facades and semitransparent roofs [13]. Other groups have used polymers or oligomers bearing reactive groups that can form a three-dimensional molecular network as solid matrix in which the charge-carrying ions can move. Very high efficiencies have been reported from three such approaches using different chemistry to achieve a network [14], [15], [16].

In this paper, we present a quasi-solid-state DSSCs utilizing a molecular network formed by a cyanoacrylate compound in which an iodide/triiodide redox couple performs the charge transport. Cyanoacrylate, the so-called “SuperGlue®”, is a reactive monomer that can be easily polymerized under ambient humidity, forming a high molecular weight polymer. The gluing process responsible for the bonding between the two glass plates of the solar cell is based on the polymerization described in Scheme 1. From a technology point of view, this is very desirable, as it provides excellent mechanical stability by keeping the substrates together. Obtaining energy conversion efficiencies of more than 4% under 100 mW/cm2 of simulated A.M. 1.5 illumination, the cyanoacrylate quasi-solid electrolyte is an ordinary and low-cost compound which has fast drying property and offers significant advantages in the fabrication of solar cells and modules as it is in itself a very good laminating agent.

Section snippets

Experimental

Titanium isopropoxide (TIP, 99.99%), tetrapropylammonium iodide (TPAI), 4-tert-butylpyridine (TBP), iodine, ethylene carbonate (EC), acetonitrile (ACN), all from Aldrich, were used as received. The titanium oxide paste (Ti-nanoxide HT) and the Ru dye (RuL2 (NCS) 2:2TBA, L: 2,2′-bipyridyl-4,4′-dicarboxylic acid, TBA: tetrabutylammonium, N-719) were bought from Solaronix. Cyanoacrylate was purchased as “SuperGlue®”(Ropid 100 Sekundenkleber from Conrad Elektronikversand, €3.59 per 20 g).

ITO-coated

Results and discussion

The photoelectrochemical power conversion in a DSSC occurs at the titanium oxide–dye-electrolyte interface. After excitation, a very efficient photo-induced electron transfer from the excited dye molecules to the titanium oxide takes place, and then the electrons migrate through the titanium oxide until they reach the ITO electrode. The electric current thus produced is passed into an external circuit to perform electrical work. Electrons reenter the cell through the Pt counter electrode and

Conclusions

We have fabricated a DSSC that incorporates a novel quasi-solid electrolyte based on cyanoacrylate and a triiodide/iodide redox couple. These materials’ combination provides solar energy conversion efficiencies of over 4% in combination with extraordinarily low cost and fast drying property. An especially noteworthy advantage is the laminating property of the cyanoacrylate (“SuperGlue®”) that allows for a very easy production of mechanically stable large area solar cells. Measurements of

Acknowledgments

We would like to thank DI M. Ratajski for the SEM images. Funding was provided by the Austrian Science Foundation (FWF), the European Commission via the Molycell project, Zhejiang Natural Science Foundation (Grant No. Y106086) and the Scientific Research Foundation for the Returned Overseas Chinese Scholars, State Education Ministry.

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