The IQE is always larger than the EQE in the visible spectrum. A low IQE indicates that the active layer of the solar cell is unable to make good use of the photons, most likely due to poor carrier collection efficiency. To measure the IQE, one first measures the EQE of the solar device, then measures its transmission and reflection, and combines these data to infer the IQE. EQE = electrons/sec photons/sec = (current) / (charge of one electron) ( total power of photons ) / ( energy of one photon ) IQE = electrons/sec absorbed photons/sec = EQE 1-Reflection-Transmission