Photoleitfähig

Photoleitfähig, or photoconductive, refers to the ability of a material to change its electrical conductivity when illuminated by light. In the absence of light, the material behaves as an insulator or a poor conductor; when photons of sufficient energy strike the material, they excite electrons from the valence band into the conduction band, creating free charge carriers and thus increasing conductivity. This effect is governed by the band structure of the material and the photon energy relative to the band gap.

The concept was first observed in the early 20th century with lead sulfide (PbS) crystals, which were used in the first practical photoconductive detectors. Since then, a wide range of semiconductors such as silicon, germanium, cadmium sulfide, and various thin-film alloys have been studied for their photoconductive properties. Organic photoconductors, including polymers and small molecules, have also been developed to enable flexible and low-cost devices.

Photoconductive materials are central to many technologies. They enable light‐sensitive switches, where illumination turns on an electrical circuit; image sensors, where a two‑dimensional array of photoconductive elements converts a light pattern into an electrical signal; and photomultiplier tubes, where the photoconductive layer initiates a cascade of electron multiplication. In solar cells, photoconductivity plays a role in the separation and transport of photogenerated charge carriers. Photolithography also relies on photoconductive photoresists that change solubility under light, allowing pattern transfer onto wafers.

Research into photoconductivity continues with a focus on increasing responsivity, reducing noise, and integrating materials into nanostructured devices. Hybrid systems combining inorganic and organic components aim to harness the advantages of both classes, potentially leading to high‑performance, low‑energy photodetectors and optoelectronic sensors.