Efficient Reductive or Oxidative Current Flow across 100 μm Using an Si Photoelectrode under High Level Injection

Abstract

The photoelectrochemistry of contacts has been investigated under high level injection conditions. Exposure of Si samples having low doping levels and long minority carrier lifetimes (>1 ms) to modest steady‐state illumination levels has produced high level injection conditions and minimal electric fields at the solid/liquid contact. Under these conditions, the solid is analogous to a large molecule, with both electrons and holes available for interfacial charge transfer (and recombination) at the solid/liquid contact. In principle, photocurrents of either sign are possible in such samples. Vectorial charge separation with a high quantum yield has been effected by selective removal of one carrier type at the back of the sample, in a fashion analogous to either oxidative or reductive quenching of a molecular excited state. Through specifying the back contact connections, the sign of the photocurrent at the solid/liquid interface, 100 μm from the initial quenching site, has been manipulated. Charge separation with high quantum yields and with ≈0% photoelectrode energy conversion efficiencies under solar simulation has been achieved using this approach.