Quantum efficiency (QE) is a measure of the ability of a solar cell to convert photons into electrical current. It is the ratio of the number of carriers collected by the solar cell to the number of photons of a given energy incident on the solar cell. The quantum efficiency may be given either as a function of wavelength or of energy.
The quantum efficiency of a solar cell is affected by various factors, including recombination effects, surface passivation, and diffusion length. Recombination effects reduce the quantum efficiency by affecting the collection probability of carriers generated near the surface or in the bulk of the solar cell. Surface passivation affects carriers generated near the surface, while diffusion length affects the collection probability from the solar cell bulk.
Researchers have achieved an unprecedented 190% quantum efficiency by using a perovskite material in a photoelectrochemical cell. The perovskite material has a crystal structure that allows it to extract hot carriers, which are highly energetic electrons that are briefly excited from their ground states when hit with enough visible light. These hot carriers can immediately convert energy into photocurrent, rather than being lost as heat.