Strain-compensated multiple stepped quantum wells (SC-MSQWs) cell for enhanced spectral response and carrier transport

In order to develop a high quality material which is both lattice-matched to GaAs and with extended absorption edge below 1000 nm for improved efficiency of III-V tandem solar cells, we have introduced In_0.16Ga_0.84As/GaAs/GaAs_0.79P_0.21 strain-compensated multiple stepped quantum wells (SC-MSQWs) solar cell. To maximize the contribution of quantum well to spectral response, we inserted a GaAs step layer between the well and the barrier, leading to stronger photo-absorption of the wells and enhanced carrier transport in the stacked wells. Combined with strain compensation between highly-strained wells and barriers, the SC-MSQWs allow us sufficient number of quantum-well stacks to obtain significant spectral response below the bandgap of GaAs. A short circuit current density 25 mA/cm² was obtained under AM1.5G illumination, which is approximately 14% higher than that of a conventional MQWs solar cell.