Most chemical reagents were purchased from Sigma-Aldrich Chemical Co. (St. Louis, MO, USA) and used as received without further purification. All the reactions were carried out under a dry nitrogen atmosphere, unless stated otherwise. Solvents were dried using the standard method. 4,4'-Dicarboxy-2,2'-bipyridine (dcbpy), 4,7-dicarboxy-1,10-phenanthroline (dcphen), 4,4'-bis(E-carboxyvinyl)-2,2'-bipyridine (dcvbpy), 4,7-bis(E-carboxyvinyl)-1,10-phenanthroline (dcvphen), and 5-(2-[2,2'-bipyridin] -5-ylethynyl)-22'-bipyridine were prepared by the methods reported previously [6,8].
1H NMR spectra were recorded using a 400 MHz NMR (Jeol, Tokyo, Japan), and chemical shifts were reported in ppm relative to the residual solvent as an internal standard. …show more content…
The P25 TiO2-powder-precursor semiconductor layers were prepared as following. Weighted P25 TiO2 powders (1g), acetylacetone (0.75 mL), polyethylene glycol (2.5 g, PEG-600), and ethyl alcohol (0.63 mL) were mixed to form the coating paste. The coating paste was stirred for 30 min. Next, a clean indium tin oxide (ITO) layer (80 nm, 30 ohm/square) on glass was prepared as the working electrode. The ITO substrate was cleaned in an ultrasonic bath of acetone for 10 min, followed by rinsing with deionized water, drying with nitrogen, and ultra-violet ozone cleaning. After that, the TiO2 paste was then coated on the pre-cleaned ITO conducting glass surface by the doctor-blading method. The coated film was dried at the room temperature for 10 min and sintered 450 °C for 90 min. Next, for dye sensitization, conducting glass with the titanium dioxide layer was immersed in complex dye solution with JW5-JW8 (0.20 wt%) in isopropyl alcohol or methyl alcohol for 16 h at room temperature. As a reference, the dye N719 was also used (Solaronix SA, Aubonne, Switzerland). The excess dyes on the glass surface were then washed away using the solvents used. Then, a Pt counter electrode was fabricated on the pre-cleaned glass surface using sputter deposition (0.2 nm/s) at a base pressure of less than 5 × 10−1 Pa. The TiO2 working electrode (with dye) and the Pt counter electrode were sealed using the spacer films of thickness 75 μm. Finally, the DSSC was obtained after filling an electrolyte with the composition of 0.05 M I2, 0.1 M LiI, and 0.5 M tert-butylpyridine in acetonitrile to the gap between the working and conter electrodes. The performance of DSSCs was measured under an illumination intensity of 100 mW cm-2 generated by an AM 1.5 light source (96000 Solar Simulator, Newport Corporation, Irvine, CA, USA). The photocurrent characteristics were measured using a source meter