Light-Induced Charge Transport within a Single Asymmetric Nanowire

Artificial photosynthetic systems using semiconductor materials have been explored for more than three decades in order to store solar energy in chemical fuels such as hydrogen. By mimicking biological photosynthesis with two light-absorbing centers that relay excited electrons in a nanoscopic space, a dual-band gap photoelectrochemical (PEC) system is expected to have higher theoretical energy conversion efficiency than a single band gap system. This work demonstrates the vectorial charge transport of photogenerated electrons and holes within a single asymmetric Si/TiO2 nanowire using Kelvin probe force microscopy. Under UV illumination, higher surface potential was observed on the n-TiO2 side, relative to the potential of the p-Si side, as a result of majority carriers recombination at the Si/TiO2 interface. These results demonstrate a new approach to investigate charge separation and transport in a PEC system. This asymmetric nanowire heterostructure with a dual band gap configuration and simultaneously exposed anode and cathode surfaces represents an ideal platform for the development of technologies for the generation of solar fuels, although better photoanode materials remain to be discovered.