GaAsP/Si dual-junction solar cells grown by MBE and MOCVD

Monolithic, direct epitaxial GaAs_0.75P_0.25/Si dual-junction (2J) solar cell structures have been grown via both molecular beam epitaxy (MBE) and metal-organic chemical vapor deposition (MOCVD). Fabricated test devices show working tandem behavior, with clear voltage addition and spectral partitioning, in both cases. Due to the thermal sensitivity of the MBE-grown tunnel junction structure, growth conditions necessary to maintain 2J activity yielded reduced quality GaAs_0.75P_0.25 top cell, while the more robust MOCVD-based tunnel junction enabled higher-quality top cell growth, resulting in overall higher performance 2J behavior. These initial prototype cells show promising performance and suggest several definite pathways for further device refinement.