New perylene polyimides containing p-n diblocks for sensitization in TiO₂ solar cells

Three novel perylene polyimides (PPIs) containing p-n diblock units were designed and synthesized for use in dye-sensitized mesoporous TiO ₂ solar cells. They all dissolve in m-cresol and N-methyl-2-pyrrolidone (NMP). Their visible light absorption, electrochemical and photoelectrochemical properties were systematically studied. The polyimides have band gap energies of 2.16, 2.19 and 2.25 eV deduced from ultraviolet-visible absorption spectra, and electron affinity (E_a) and ionization potential (IP) of -3.93 and 6.10 eV for PPI1, -3.94 and 6.13 eV for PPI2, -3.93 and 6.59 eV for PPI3, respectively, deduced from cyclic voltammogram. Experimental data show that introduction of 4,4′-bisaminetriphenylamine cannot only greatly enhance optic-electro conversion efficiency, but also enhance the dissolubility which in favorable for making the devices. The relationship of structure and properties of PPI is discussed and the mechanism of photocurrent generation is explained.