Synthesis and preliminary photovoltaic behavior study of a soluble polyimide containing ruthenium complexes

Aiming to prepare photovoltaic materials with light and thermal stability, ruthenium complexes with broad absorption in the visible region were introduced to a polyimide, bpy-PI, which contains a bipyridine ligand in each repeating unit. The chemical structures of the monomers and polymers were confirmed by H-1 NMR, IR, and elemental analysis. The prepared polyimide containing ruthenium complexes (bpy-PI-Ru) showed good solubility in common organic solvents such as DMF, NMP, DMSO and DMAc. UV-vis measurements revealed that bpy-PI-Ru exhibits very broad absorptions in the range 350-750 nm due to the introduction of ruthenium complexes. Such absorption enhancement would enable the polymer to harvest solar light in the visible region. The onset oxidation potential of bpy-PI-Ru was measured as 0.68 V (vs. SCE), which is about 0.06 V lower than that of bpy-PI. The band gap of bpy-PI-Ru is 1.35 eV as measured by cyclic voltammetry. Solar cell devices were fabricated based on bpy-PI-Ru or the blend of bpy-PI-Ru and PCBM. Current density-voltage (J-V) measurement of the devices showed a typical rectifying behavior under a 55 mW cm(-2) compact white arc lamp. The open-circuit voltages and short-circuit densities were measured to be in the ranges 0.19-0.52 V and 0.0015-0.38 mA cm(-2), respectively. The short-circuit density could be further improved by anode modification through deposition of PEDOT:PSS on ITO surface.