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

Carbon nanohorns (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 SnO ₂ films were cast onto the OTE (OTE/SnO₂). The CNH-H ₂P 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 nanohorns 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.