For IQE measurement the monochromator used in the external QE measurement system is fitted with an IQE attachment.  This attachment is an integrating sphere sample chamber which allows all the transmitted and reflected light by the solar cell to be captured and measured.  For IQE measurements the cell is placed in the sample holder attached to the integrating sphere.  A detector mated to the integrating sphere port orthogonal to the sample holders measures the reflected and transmitted light.
 
For cells that are small enough to fit in the IQE sample holder, bias light can be fed from a bias light source into the integrating sphere and onto the cell, so that the external QE itself can be measured with the IQE attachment.  (As with the external QE unit, lock-in electronics and an I-V test system are used as well).  In the case of larger cells however, a separate external QE system is needed to obtain IQE based on full area measurements.