Dye-Sensitized Solar Cells Based on Polymer Electrolytes

Abstract

Dye-sensitized solar cells (DSSCs) using organic liquid electrolytes have received significant attention because of their low production cost, simple structure and high power conversion efficiency [1-5]. Recently, the power conversion efficiencies of DSSCs using Ruthenium complex dyes, liquid electrolytes, and Pt counter electrode have reached 10.4 % (100 mW/cm2, AM 1.5) by Gratzel group [6]. However, the important drawback of DSSCs using liquid electrolyte is the less long-term stability due to the volatility of the electrolyte contained organic solvent. In the viewpoint for commercialize, durability is a crucial component. Then, gel electrolytes are being investigated to substitute the liquid electrolytes [7-10]. One way to make a gel electrolyte is to add organic or inorganic (or both) materials. In the past decades, many studies have been carried out on this kind of gel electrolyte, and great progress has been achieved [11-12]. The advantages of them include; limited internal shorting, leakage of electrolytes and non-combustible reaction products at the electrode surface existing in the gel polymer electrolytes [13-14]. However, because of their complicated preparing technology and poor mechanical strength, they cannot be used in commercial production [15-16]. To overcome this problem, the polymer membrane is soaked in an electrolyte solution that has been examined [17-19]. To prepare the polymer membrane for polymer electrolyte, a number of processing techniques such as drawing [20], template synthesis [21-22], phase separation [23], electrospinning [24], etc. have been used. Among of these, the electrospinning technology is a simple and low-cost method for making ultra-thin diameter fibers. This technique, invented in 1934, makes use of an electrical field that is applied across a polymer solution and a collector, to force a polymer solution jet out from a small hole [25]. When the diameters of polymer fiber materials are shrunk of micrometers to submicrons or nanometers, several amazing characteristics appear such as a very large surface area to volume ratio, flexibility in surface functionalities, and superior mechanical performance compared to any other known forms of this material [26]. In recent years, the electrospinning method has gained greater attention. A vastly greater number of synthetic and natural polymer solutions were prepared with electrospun fibers, such as poly(ethylene oxide) (PEO) in distilled water [27], polyurethane in N,N-dimethylformamide (DMF) [28], poly(e-caprolactone) (PCL) in acetone [29], PVDF in acetone/ N,N-dimethylacetamide (DMAc) (7:3 by weight) [30], and regenerated cellulose in 2:1(w/w) acetone/DMAc [31].