Multijunction Ga0.5In0.5P/GaAs Solar Cells Grown by Dynamic Hydride Vapor Phase Epitaxy

We report the development of Ga_0.5In_0.5P/GaAs monolithic tandem solar cells grown by dynamic hydride vapor phase epitaxy, a III-V semiconductor growth alternative to metalorganic vapor phase epitaxy with the potential to reduce growth costs. The tandem device consists of 3 components: a 1.88 eV band gap (E_G) Ga_0.5In_0.5P top cell, a p-Ga_0.5In_0.5P/n-GaAs tunnel junction, and a 1.41 eV rear heterojunction GaAs cell. The open circuit voltage (V_OC) and fill factor are 2.40 V and 88.4%, respectively, indicative of high material quality. Electroluminescence measurements show that the individual V_OC of the top and bottom cell are 1.40 and 1.00 V, respectively, yielding E_G-voltage offsets (W_OC) of 0.48 and 0.41 V. The W_OC of the top cell is higher because of an unpassivated front surface rather than the bulk material quality. The Ga_0.5In_0.5P top cell limits the current of this series-connected device for this reason to a short-circuit current density (J_SC) of 11.16 ± 0.15 mA/cm² yielding an overall efficiency of 23.7% ± 0.3%. We show through modeling that thinning the emitter will improve the present result, with a clear pathway toward 30% efficiency with the existing material quality. This result is a promising step toward the realization of high-efficiency III-V multijunction devices with reduced growth cost.