III-V multi-junction solar cell using metal wrap through contacts

Abstract

The Solar cell front side is a key design point for improved cell efficiency as a trade is made between optical losses (shadowing effect) and electrical losses (resistance). One solution consists in frontside contacts report to the cell’s backside using through device conductive vias. By this way metal shadowing could be drastically reduced without increasing resistive losses. Such architecture is called Metal Wrap Through (MWT) and has been developed on silicon solar cells. Its application to III-V Multi-Junctions Solar Cells (MJSC) could be of great interest and has been simulated and studied for several years. We present here first functional MWT III-V dual-junction solar cells. Prototype developments have been based on inverted tandem solar cell (GaInP/GaAs) epitaxial structures grown on GaAs substrates. Front side contacts have been reported on the device’s backside using specifically adapted Trough Semiconductor Via (TSV) technologies. Finally, the III-V active film was transferred on a conductive receiver by copper to copper (Cu//Cu) direct metal bonding. Morphological and chemical characterizations showed metallized and isolated contacts going through the tandem solar cell’s structure. Electrical characterizations displayed many functional cells across 100mm wafers reaching efficiencies up to 26.3% @1 sun AM1.5d spectrum with a fill factor (FF) of 87.1%. Under concentration the efficiency raised up to 28.3% @167 suns. Beside these demonstrators, developed processes open ways to various possibilities such as large area III-V MJSC receivers.