Investigation of Rear-Emitter GaAsP Top Cells for use in III-V/Si Tandem Photovoltaics

摘要

Rear-emitter n/p^{+ cells were investigated as an alternative to conventional n+/p front-emitter cells for potentially increased tolerance against threading dislocation-induced lifetime degradation. A comparison of MOCVD-grown front- and rearemitter GaAs_0.75 P_0.25 cells for use in III-V/Si tandem solar cells demonstrates that the rear-emitter design has lower dark current and higher V_OC, but lower J_SC. Analysis of the collection dynamics in the rear-emitter cell structure indicates a heightened sensitivity to front-surface and Al_0.66In_0.33P/GaAs_0.75P_0.25 (window/base) interface recombination, which is exacerbated by Fermi level pinning at the window/air interface. This work indicates that the rear-emitter design is a promising alternative to front-emitter structures due to its improved minority carrier lifetime and therefore V_OC, but careful optimization of device structure, and possibly material quality, is necessary to improve the minority carrier collection.}