IPCE

IPCE, or Incident Photon-to-Current Efficiency, is a metric used to describe how efficiently a photovoltaic or photoelectrochemical device converts incident photons at a given wavelength into electrical current. It is typically expressed as a percentage and is defined as the ratio of the generated photocurrent to the incident photon flux. A common mathematical form is IPCE(λ) = Iph(λ) / [q × Φ(λ)], where Iph is the photocurrent at wavelength λ, q is the elementary charge, and Φ(λ) is the incident photon flux. When expressed with light power instead of photon flux, IPCE(λ) can be written as IPCE(λ) = (1240 × Jsc(λ)) / [P_in(λ) × λ], with Jsc the short-circuit current density and λ the wavelength in nanometers.

IPCE is measured by illuminating the device with monochromatic light of known intensity while recording the short-circuit current. A calibrated detector monitors the incident light to determine Φ(λ). The measurement setup typically includes a light source (often a xenon lamp), a monochromator or filter, and a current-measuring unit, sometimes with a lock-in amplifier to improve signal-to-noise. The resulting IPCE spectrum reveals the device’s spectral response and provides insight into absorption, charge collection, and recombination losses.

Relation to other quantum efficiency concepts: IPCE is commonly used interchangeably with external quantum efficiency (EQE). The internal quantum efficiency (IQE) relates to IPCE via IQE(λ) = IPCE(λ) / A(λ), where A(λ) is the absorptance of the active layer. IPCE analyses are widely used in solar cells, dye-sensitized solar cells, quantum dot devices, and photoelectrochemical cells.