Wafer bonded 4-junction GaInP/GaAs//GaInAsP/GaInAs concentrator solar cells

Multiple-junction solar cells made from III-V compound semiconductors are delivering the highest solar-electric conversion efficiencies. Increasing the number of junctions offers the potential to reach higher efficiencies. Direct wafer bonding offers a unique opportunity to combine lattice mismatched materials through a permanent, electrically conductive and optically transparent interface. In addition, the use of Smart Cut (TM) technology, associated with its material recycling capabilities allows from a cost perspective the use of expensive bulk material such as InP. Combination of both technologies opens new opportunities to deliver cost effective high efficiency solar cells. In this respect, we have been able to demonstrate a record efficiency of 44,7% with a wafer bonded 4-junction GaInP/GaAs//GaInAsP/GaInAs concentrator solar cell with bandgap energies of 1.88/1.44//1.11/0.70 eV respectively. The bandgaps are chosen to be close to optimal for conversion under concentrated sunlight [1]. This paper presents the improvements made to achieve the world record result leading to higher efficiencies and lower cost.