Characterization and photoelectrochemical properties of nanostructured thin film composed of carbon nanohorns covalently functionalized with porphyrins

Carbon nanohoms (CNHs) covalently functionalized at the conical tips with porphyrin (H2P) moieties were used to construct photoelectrochemical solar cells. Electrophoretic deposition was applied to fabricate films of the modified CNHs onto optically transparent electrodes (OTE) while nanostructured SnO2 films were cast onto the OTE (OTE/SnO2). The CNH-H2P film on the nanostructured SnO2 electrode exhibited an incident photon to current conversion efficiency (IPCE) of 5.8% at an applied bias of +0.2 V vs SCE in a standard three-compartment electrochemical cell. The measured IPCE was found greater than the one observed for the sum of the single components, namely CNHs and H2P films onto the SnO2 electrode. Fluorescence lifetime measurements revealed that photoinduced electron transfer from the singlet excited state of the porphyrin to the nanohoms takes place, while direct electron injection from the reduced nanohorns to the conduction band of the SnO2 electrode occurs. These processes are responsible for the photocurrent generation.