Incident Photon-to-Current Efficiency (IPCE) is the wavelength-resolved efficiency of a photoelectrode: of the photons arriving at a given wavelength, how many contribute electrons to the external circuit? It is the measurement that reveals where a device actually works, and where it merely absorbs.
IPCE equals the photocurrent at wavelength λ divided by the photon flux at that wavelength, a straightforward ratio experimentally, but every term hides calibration work. The measured photocurrent must be steady-state (or explicitly transient), and the photon flux must be measured at the electrode position with the same optical path as the experiment.
A monochromator or tunable source; a calibrated photodetector to measure flux at each wavelength; an electrochemical workstation holding the electrode at defined bias; and a shutter or chopper for transient and steady protocols. Bias matters, measure IPCE at a stated potential, because IPCE is a function of both wavelength and bias.
At each wavelength: measure flux at the electrode plane, expose the electrode, record photocurrent to steady state, subtract dark current, and move on. Re-verify flux periodically, monochromator output drifts with lamp age and slit changes. Wavelength steps should be fine enough to resolve spectral features, typically 10 nm across the absorption range.
Subtract dark current; use the correct photon energy at each wavelength; state the bias and electrolyte. Integration of IPCE against the solar spectrum (with reflection losses considered) should reproduce the short-circuit current from solar simulator measurements, a powerful internal consistency check.
Perfectlight's PEC systems and solar test platforms support spectral efficiency measurements; see solutions.
