photogenerated

Photogenerated is an adjective describing species or phenomena produced directly by the absorption of light. In materials science and chemistry, photogenerated typically refers to charge carriers—electrons and holes—that are created when photons with sufficient energy excite a material, most commonly a semiconductor. Absorption of a photon with energy above the bandgap promotes an electron from the valence band to the conduction band, leaving behind a positively charged hole. These photogenerated electrons and holes can migrate to interfaces, where they can participate in redox reactions, or recombine, releasing energy as heat or light.

In photocatalysis, photogenerated electron-hole pairs drive chemical transformations, such as the oxidation of organics and reduction of pollutants, or water splitting at suitable catalysts. In photovoltaics, the separation and collection of photogenerated carriers generate electric current. The efficiency of these processes depends on the lifetime and diffusion length of the carriers, the alignment of energy bands at interfaces, surface recombination rates, and the presence of traps or defects.

Photogenerated excitons—bound electron-hole pairs—can dominate in some materials, especially insulators or organic semiconductors, whereas in many inorganic semiconductors free carriers are more relevant. Materials engineering, such as doping, nanostructuring, and surface modification, aims to improve charge separation and reduce recombination of photogenerated species.

Techniques to study photogenerated species include photoluminescence spectroscopy, transient absorption spectroscopy, and time-resolved microwave conductivity, which provide information about lifetimes, recombination pathways, and charge-transfer dynamics.