Potentially modulated multi-quantum wells for high-efficiency solar cell applications

The expected high performance of multi-quantum well (MQW) solar cells depends not only on the material quality ensuring minimum non-radiative recombination losses at the heterointerfaces, but also on the escape rate of photogenerated carriers out of QWs into the “base” region having minimum radiative losses within QWs. For this, we propose and investigate potentially modulated MQW solar cell structures, for which the MQW structure is modified from a series of conventional square-shaped QWs to “step-like” potentially modulated QWs. We have studied “two-step” and “three-step” MQWs introduced into the intrinsic region of GaAs p-i-n solar cells. Compared with a square-shaped MQW cell, a three-step modulated MQW cell having the same average potential well depth showed photoluminescence characteristics with a smaller thermal activation energy and higher average carrier temperature. The dark current characteristics also indicated that photogenerated carriers escape out of QWs more efficiently in this type of structure.