Advances in wide-bandgap III-V solar cells

III-V multi-junction solar cells have yielded the highest solar cell efficiencies for nearly three decades and recently achieved record efficiencies approaching 40% under standard conditions and 50% under concentrated sunlight. Such high efficiencies are currently only possible using four or more junctions to partition the broad solar spectrum into bins where each subcell efficiently collects a narrow range of photon energies. High-efficiency, wide-bandgap (1.7–2.2 eV) absorbers play a crucial role in multi-junction solar cells by efficiently converting visible photons into electrons and delivering them at high voltage. Since all subcells are interconnected in series, the widest bandgap junction produces both the highest voltage and highest power in the stack. Wide-bandgap absorbers also present the greatest materials challenges in the stack, including high aluminum content, lattice mismatch, lack of heterojunction barriers, and the sensitivity of phosphides to defects such as vacancies and oxygen. We review the history, current status, and opportunities for wide-bandgap III-V solar cells, ranging from ∼1.7 eV for the top subcell of III-V/Si hybrid tandems to >2.2 eV for the top subcell of a 6+ junction stack. Future directions and recommendations to overcome remaining materials and device challenges will be discussed.