Multijunction III-V solar cells: recent and projected results

The authors discuss Varian´s strategy for developing high-efficiency multijunction cells. Cell performance data are reviewed and compared to computer modeling performance projections for two and three-junction cascade cells. Results are presented for single-junction and multijunction monolithic structures fabricated with the AlGaAs-GaAs-InGaAs materials system grown by metal-organic chemical vapor deposition. The problems and progress for lattice-matched and lattice-mismatched structures and cell interconnects are discussed and assessed. It is concluded that the latest results are significant steps towards a demonstration of the viability of cascade cells. The hurdles to be overcome in an effort to achieve efficiencies above 30% are discussed.