Two-element cascade Al-Ga-As solar cell

Monolithic cascade solar cells in which each cell is used as an independent power supply have been fabricated by liquid-phase epitaxy on GaAs substrates in the (100) orientation. The monolithic cascade solar cells consist of two photocells: (1) the upper cell with a p-n junction in Al(y)Ga(1-y)As and a protective window of Al(x)Ga(1-x)As, where x is 0.9 or more and (2) the lower cell with a p-n junction in gallium arsenide, for which an Al(y)Ga(1-y)As solid solution serves as a window. The efficiency of a monolithic cascade structure with a gap width of 1.65 eV, fabricated in a single technological process, is 18%, i.e. twice the efficiency reported previously for a GaAs-AlAs cascade cell.