Why can semiconductor electrodes respond to light when metal electrodes generally do not?

A semiconductor's band gap lets it absorb light to create electron–hole pairs, and its internal space-charge field separates them to drive interfacial reactions, whereas a metal's abundant free electrons relax absorbed energy as heat without sustained charge separation.

What is the flat-band potential?

It is the electrode potential at which there is no band bending and no space-charge field in the semiconductor; it is a key reference quantity, commonly obtained from the intercept of a Mott–Schottky plot.

Semiconductor Electrochemistry and Photoelectrochemistry

Semiconductor electrochemistry treats electrodes whose interfacial potential drop and reactivity are governed by a space-charge region within the solid, enabling light-driven reactions in photoelectrochemical cells.

Definition

The electrochemistry of semiconductor electrodes, in which a space-charge region inside the solid controls charge transfer, and where illumination can generate the charge carriers that drive electrode reactions.

Scope

This topic covers the distinctive behavior of semiconductor electrodes: the space-charge layer and band bending, flat-band potential and its determination by Mott–Schottky analysis, the role of conduction and valence bands in electron transfer, and photoelectrochemistry in which absorbed light generates carriers that drive oxidation or reduction. It includes applications to solar water splitting and dye-sensitized cells.

Core questions

How does a semiconductor electrode differ from a metal in its interfacial potential distribution?
What are the flat-band potential and band bending, and how are they measured?
How does absorbed light generate carriers that drive electrochemical reactions?
How do photoelectrochemical cells convert light into chemical or electrical energy?

Key theories

Space-charge layer and band bending: Because a semiconductor has few mobile carriers, much of the interfacial potential drop occurs inside the solid as a space-charge region; the resulting band bending controls the energetics and direction of charge transfer, analyzed via Mott–Schottky plots.
Photoelectrochemical carrier generation: Light with energy above the band gap creates electron–hole pairs; the space-charge field separates them so that minority carriers drive interfacial redox reactions, the basis of photoelectrochemical water splitting and solar cells.

Clinical relevance

Semiconductor electrochemistry underpins photoelectrochemical solar fuel production, including water splitting for hydrogen, dye-sensitized and other solar cells, photocatalytic environmental remediation, and the etching and processing of semiconductors in electronics manufacturing.

History

Gerischer developed the theory of charge transfer at semiconductor electrodes in the 1960s; Fujishima and Honda's 1972 demonstration of photoelectrochemical water splitting on titanium dioxide launched intensive research into solar fuels and photoelectrochemistry.

Key figures

Akira Fujishima
Kenichi Honda
Heinz Gerischer
Rüdiger Memming

Seminal works

fujishima1972
memming2015
bard2001

Frequently asked questions

Why can semiconductor electrodes respond to light when metal electrodes generally do not?: A semiconductor's band gap lets it absorb light to create electron–hole pairs, and its internal space-charge field separates them to drive interfacial reactions, whereas a metal's abundant free electrons relax absorbed energy as heat without sustained charge separation.
What is the flat-band potential?: It is the electrode potential at which there is no band bending and no space-charge field in the semiconductor; it is a key reference quantity, commonly obtained from the intercept of a Mott–Schottky plot.