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 1H 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.