Enhanced carrier escape in MSQW solar cell and its impact on photovoltaic performance

Summary form only given. A multiple stepped quantum wells (MSQWs) solar cell, in which GaAs stepped-potential layers are sandwiched between strain-balanced InGaAs wells and GaAsP barriers, has been proposed and improvement in short-circuit current and fill factor has been demonstrated in our previous analysis. We here studied carrier escape kinetics from the wells, in comparison between the MSQW and the normal multiple quantum well (MQW) structures. Radiative recombination rate of carriers was examined by time-resolved photoluminescence (PL) and a slower radiative recombination was observed for MSQWs than for MQWs. Carrier escape efficiency from the wells was examined in terms of temperature-dependent PL and a smaller thermal activation energy of carrier escape was observed for MSQWs than for MQWs. Such enhanced carrier escape in the case of MSQWs allowed us to stack sufficient number of quantum wells to increase short-circuit current without degradation in fill factor. This is in contrast to the normal MQW cell, in which larger total thickness was necessary for increasing short-circuit current than the case of MSQWs and degradation in fill factor was unavoidable with a large number of quantum wells.