We investigated the charge separation processes in three types of III-V solar cells with different device structures using power dependence of time-resolved photoluminescence (PL) decays. The samples were a GaAs single junction and InGaP and GaAs subcells of triple-junctions solar cells prepared with different growth techniques. All p-n junctions showed same systematic changes in the PL decay profiles with increasing excitation power. The data evidences that charge separation and recombination carrier dynamics can be probed directly in a wide range of devices with time-resolved PL decays. The optical method allows to determine the subcells electrical behavior from the PL decay time constants.