Hot-carrier generation and extraction in InAs/GaAs quantum dot superlattice solar cells

We demonstrate hot-carrier (HC) generation and extraction processes in InAs/GaAs quantum dot superlattice (QDSL) solar cells with the excitation energy tuned below the GaAs band edge at 15 K. The short-circuit current density and the open-circuit voltage originated from the HC extraction are enhanced by increasing the number of the QDSL layers owing to the increased absorptivity in the QDSLs. The short-circuit current density demonstrates an almost linear dependence with increasing excitation density and increases with increasing excitation energy, which reflects the absorption coefficient in the QDSLs. Conversely, the open-circuit voltage tends to saturate to the same value independently from the excitation energy, indicating that the hot electrons extracted to the conduction band edge of GaAs are retrapped at the open-circuit condition due to a low built-in electric field of ∼1.3 kV cm⁻¹. (paper)