A bioinspired dye sensitized solar cell based on a rhodamine-functionalized peptide immobilized on nanocrystalline TiO2

A dodecapeptide (AMRKLPDAPGMH) functionalized with a tetramethylrhodamine (TAMRA) chromo- phore at the N-terminus was immobilized on nanocrystalline TiO2. The optical and binding properties of the peptide layer immobilized on the titania surface were characterized by UV–vis absorption, steady- state fluorescence and X-ray photoelectron spectroscopies. Circular Dichroism experiments and Molecular Mechanics calculations showed that the predominant conformation populated by the peptide scaffold brings Arg3, Lys4 and Asp7 in the correct position for linking the TiO2 surface. Photocurrent generation experiments were therefore carried out to determine the photon-to-current conversion efficiency (IPCE) of a Grätzel-like Dye Sensitized Solar Cell (DSSC), the photoactive unit of which is formed by TAMRA-AMRKLPDAPGMH/TiO2. The measured IPCE amounted to 0.65%, a value that is definitely low, but superior to those previously reported for similar bioinspired DSSCs. This result can be ascribed to the light-harvesting properties of the TAMRA chromophore and to the unique structural properties of the peptide spacer.