This question is old but for others who might be interested, a very simple measurement can be done using an oscilloscope and a light source with fast turn-off decay. (Some solar simulators have some inner capacitance that prevents fast turn off) You can use a mechanical shutter too. A more precise method is to use a bias light source and a pulsed laser. It depends on the time-scale needed. For example, perovskite solar cells have a slow decay in the order of several seconds and the first method is adequate.