Novel Broadly Absorbing Sensitizers with Cyanovinylene 4-Nitrophenyl Segments and Various Anchoring Groups: Synthesis and Application for High-Efficiency Dye-Sensitized Solar Cells

Abstract

Three new organic sensitizers D1, D2, and D3 with carboxy, acid anhydride, and hydroxy anchoring groups, respectively, and terminal cyanovinylene 4-nitrophenyl segments were synthesized. Their absorption spectra were broad with long wavelength absorption maximum approximately at 620 nm and optical band gap of 1.64−1.73 eV. We have fabricated the quasi-solid-state dye-sensitized solar cells (DSSCs) using these dyes and found that the power conversion efficiency (PCE) is of the order D1 > D2 > D3. The maximum PCE is about 4.58% with D1, which is further improved up to 5.80% when chenodeoxyacholic acid (CDCA) coadsorbent is added in the dye solution. The superior PCE for the DSSC with D1 has been attributed to the higher energy gap between the LUMO level of D1 and the conduction band of the TiO2 as compared to the other two dyes. The further improvement in the PCE with the addition of the coadsorbent has been attributed to the longer electron lifetime, which leads to reduction in back recombination of injected electrons with electrolyte. The PCE of the DSSC based on D1 has been improved up to 6.9% with the incorporation of poly(vinylidene fluoride) (PVDF) in the polymer gel electrolyte. This has been correlated with the ionic conductivity of the polymer electrolyte blend.