Photoelectrochemistry of Stacked-Cup Carbon Nanotube Films. Tube-Length Dependence and Charge Transfer with Excited Porphyrin

Abstract

Photoelectrochemical solar cells are constructed with stacked-cup carbon nanotubes (SCCNT) on optically transparent electrodes (OTE). Three SCCNT samples with different tube lengths (long type, L-SCCNT; medium type, M-SCCNT; and short type, S-SCCNT) were electrophoretically deposited on OTE/SnO2 electrodes to probe the tube-length dependence of the photoelectrochemical behavior. The maximum incident photon-to-photocurrent efficiency (IPCE) of 19% is attained at an applied bias potential of 0.2 V vs SCE in OTE/SnO2/L-SCCNT. The power conversion efficiencies (η) of SCCNT-modified electrodes increase with increasing tube length. The maximum power conversion efficiency (η) of OTE/SnO2/L-SCCNT electrode is determined to be 0.11%, which is about 6 times greater than that of the OTE/SnO2/S-SCCNT electrode (0.018%). Molecular assemblies composed of S-SCCNT and 5,15-bis(3,5-di-tert-butylphenyl)porphyrin (H2P) prepared in acetonitrile/toluene (5/1, v/v) were deposited as three-dimensional arrays onto nanostructured...