Abstract We report the development of Ga 0.5 In 0.5 P/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 0.5 In 0.5 P top cell, a p‐Ga 0.5 In 0.5 P/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 0.5 In 0.5 P 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/cm 2 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.
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