A Superlattice Solar Cell With Enhanced Short-Circuit Current and Minimized Drop in Open-Circuit Voltage

A quantum-well (QW) solar cell including InGaAs wells is a promising candidate for the purpose of current matching in InGaP/GaAs/Ge tandem solar cells by extending the edge of quantum efficiency to longer wavelengths. Even though QWs increase short-circuit current by the extended effective band edge, they tend to obstruct carrier transport and degrade the efficiency of a cell. Therefore, a superlattice (SL) structure has been proposed to prevent the recombination of carriers inside of the wells and, more importantly, to enable carriers to tunnel to a neighboring well, leading to an efficient carrier transportation in such a photovoltaic device. In this paper, a SL solar cell was implemented with a strain-balancing technique. It exhibited excellent performance: Enhanced photocurrent (3.0 mA/cm $^2$ ) with minimized drop (0.03 V) in open-circuit voltage. Behind these achievements, substantial contribution of tunneling transport has been confirmed for the SL cell by external quantum efficiency measurement at 77 K.