Synthesis, photophysics of two new perylene bisimides and their photovoltaic performances in quasi solid state dye sensitized solar cells

Abstract

Two new symmetrical compounds A and P based on perylene-anthracene and perylene-pyrene, respectively, were synthesized and characterized by FT-IR, 1H NMR, TGA and TMA. These compounds contained tert-butyl groups which enhanced their solubility, decomposed above 400 °C and gave char yields of 46–65% at 800 °C in N2. Compound A showed significantly higher glass transition temperature (124 °C) than P (75 °C). Their absorption spectra were broad with longer wavelength absorption at 467–525 nm and optical band gap of 2.05 eV. The solutions of the compounds emitted green-yellow light with maximum at 555 nm, while their films were not photoluminescent. The compound A shows better photovoltaic response than compound P. Quasi solid state dye sensitized solar cells (DSSCs) have been fabricated employing compound A as sensitizer and polymer sol gel as electrolyte and characterized through the current–voltage characteristics in dark as well as under illumination and electrochemical impedance spectra. We found that the Al2O3 modification of TiO2 layer significantly improves the dye absorption resulting in enhancement of power conversion efficiency (PCE) (from 1.15 to 2.13%) which is attributed to the increase in electron lifetime and reduction in back transfer of electrons. Finally, the TiO2 has been incorporated into the polymer electrolyte gel to improve the power conversion efficiency (3.42%) of the quasi solid state DSSC. The faster electron diffusion in the device, the high ionic conductivity and the low activation energy of the polymer electrolyte are also responsible for enhanced PCE, when TiO2 nano-particles are incorporated in the polymer electrolyte.