Quasi-solid state dye-sensitized solar cells-based gel polymer electrolytes with poly(acrylamide)–poly(ethylene glycol) composite

https://doi.org/10.1016/j.jphotochem.2005.12.015Get rights and content

Abstract

A novel gel polymer electrolyte based on poly(acrylamide)–poly(ethylene glycol) composite and binary organic solvent was prepared. And the highest ionic conductivity of the gel polymer electrolyte was 1.94 mS cm−1 under the ambient atmosphere. The polymer gel electrolyte based on the composite of poly(acrylamide)–poly(ethylene glycol), the binary organic solvent of ethylene carbonate and propylene carbonate and the additive of 4-tert-bytylpyridine has been employed to fabricate quasi-solid state dye-sensitized solar cell with an overall conversion efficiency of approximately 3% under irradiation of 60 mW cm−2.

Introduction

Dye-sensitized solar cells (DSSC) based on sensitization of TiO2 nanocrystalline by photoexcited dye molecules have been investigated intensively because of its lower cost and potential alternatives to traditional photovoltaic device [1], [2], [3]. light-to-electrical energy conversion efficiencies of DSSC based on liquid electrolytes using organic compound, such as acetonitrile, propylene carbonate and ethylene carbonate as solvent and iodide/triiodide (I/I3) redox couple as electrolyte have reached 10–11% under irradiation of AM 1.5 [2], [3], [4], [5], [6], [7]. However, this type of liquid-junction cell remains some problems including low long-term stability which caused by organic solvent evaporation and leakage of liquid electrolytes, high temperature instability and difficulties in sealing the devices [8].

To overcome these problems, much effort has been made to replace the liquid electrolytes with solid or quasi-solid type charge transport materials [9], [10], [11], [12]. Compared with other kinds of charge transport materials, the gel polymer electrolytes have some advantages including high ionic conductivities which are achieved by “trapping” a liquid electrolyte in polymer cages formed in a host matrix, good contacting and filling properties with the nanostructured electrode and counter electrode. Therefore, the gel polymer electrolytes have been attracting intensive attention. Up to the present, several types of gel electrolytes based on different kind of polymers have already been used in quasi-solid state dye-sensitized solar cells [12], [13], [14].

Poly(acrylamide) possess carbonyl group and amine group on its molecular chain [15], also poly(ethylene glycol) have many hydroxyl group on its molecular chain. It is expected that the interaction between sensitized dye and the matrix of gel polymer can be improved based on the hydrogen bond interaction between the carbonyl group on sensitized dye and the carbonyl group, amine group and hydroxyl group on matrix of gel polymer electrolyte. On the other hand, the ionic conductivity of the gel polymer electrolyte can be enhanced according to the complexation from carbonyl group, amine group and hydroxyl group on poly(acrylamide) and poly(ethylene glycol) to K+ ions in electrolyte. Consequently, the overall conversion efficiency of the DSSC can be enhanced. In this paper, using poly(ethylene glycol) as both reactant and plasticizer, a novel homogeneous poly(acrylamide)–poly(ethylene glycol) composite without phase separation was synthesized. Using the composite as matrix, and 4-tert-bytylpyridine as additive, the binary organic compounds ethylene carbonate and propylene carbonate as solvent, a gel polymer electrolyte with quasi-solid state was prepared. Further, a dye-sensitized solar cell was fabricated by sandwiching the gel polymer electrolyte.

Section snippets

Materials

Poly(ethylene glycol) with average molecular weight 400 (PEG-400), acrylamide monomer, ammonium persulfate, potassium iodide, iodine, ethylene carbonate (EC), propylene carbonate (PC) and γ-butyrolactone (γ-BL) were all A.R. grade and all purchased from Xilong Chemicals. PEG-400 was dried at 120 °C for 12 h before used. Other reagents were used without further treating before using.

Conducting glass plates (FTO glass, Fluorine doped tin oxide over-layer, sheet resistance 8 Ω cm−2, purchased from

Thermogravimetric analysis of polymer matrix

As the gel polymer matrix, the thermal stability of poly(acrylamide)–poly(ethylene glycol) composite must satisfy the requirement of the dye-sensitized solar cells in practical application. Therefore, the thermogravimetric analysis of the composite was examined.

Fig. 1 exhibits the thermogravimetric curve of polymer matrix. It shows that before thermal degradation, both the poly(acrylamide)–poly(ethylene glycol) composite and the poly(acrylamide) have weight lost, which is due to absorbent water

Conclusions

Gel polymer electrolyte based on the composite poly(acrylamide)–poly(ethylene glycol) and binary organic solvent was prepared successfully. The thermal stability, ionic conductivity of the gel polymer electrolyte, as well as the influence on the photoelectronic properties of DSSC were investigated, it is found that thermal stability of the composite satisfy the requirement of DSSC. The compositions and structure of solvent and additive affect the ionic conductivity of the gel polymer

Acknowledgement

The authors gratefully acknowledge the financial support of the National Natural Science Foundation of China (No. 50572030, 50372022).

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