Photogeneration

Photogeneration is the physical process by which absorbed photons create charged carriers—electrons and holes—in a material. In a semiconductor, a photon with energy equal to or exceeding the bandgap promotes an electron from the valence band to the conduction band, leaving a hole behind. The resulting electron‑hole pair can migrate apart under internal electric fields or recombine radiatively or non‑radiatively.

The rate of photogeneration, G, is given by G = α(λ)I(λ)/ℏω, where α(λ) is the absorption coefficient, I(λ) the photon flux, and ℏω the photon energy. In devices, photogeneration efficiency is quantified by the internal quantum efficiency (IQE), the ratio of generated carriers to incident photons, and the external quantum efficiency (EQE), which includes optical losses.

Photogeneration is the core mechanism in many optoelectronic technologies. In photovoltaic cells, photogenerated carriers are separated by a built‑in junction to produce electrical current. Photoluminescent and light‑emitting diodes rely on radiative recombination of photogenerated electrons and holes to emit light. Photoconductive detectors convert photogeneration into measurable conductance changes. In photochemical applications, photo‑excited carriers initiate reactions, such as in photocatalytic water splitting.

Materials with strong absorption and long carrier lifetimes—such as crystalline silicon, gallium arsenide, and perovskites—exhibit high photogeneration efficiency. Advances in nanostructured materials, quantum dots, and plasmonic enhancement aim to increase absorption and carrier separation, thereby improving device performance across the electromagnetic spectrum.