DEVELOPMENT OF ULTRA-THIN ONE-SIDE CONTACTED GaAs SOLAR CELLS FOR MECHANICALLY STACKED MULTI-JUNCTION SOLAR CELLS

The approach of mechanically stacking cells allows more freedom on cell design and material choice for multi-junction solar cells. Since there is no requirement on current matching, mechanically stacked cells have a high performance potential, and are not sensitive to spectrum variations. Recently at IMEC, we have demonstrated ultra-thin substrate-free GaAs solar cells, which will be used as a component cell in a mechanically stacked multi-junction configuration. The GaAs cell substrate is completely removed, to avoid infrared losses for the bottom cell and to reduce the bulkiness of the mechanical stack (only one substrate without any extra fixtures). At the same time, the released substrates can be reused, keeping the cell cost-efficient. Moreover, the cell is one-side contacted, allowing relatively easy interconnections. An efficiency of 23.4% was achieved (AM1.5g), for a thin GaAs solar cell mechanically stacked on a separate, inactive Ge substrate. The work towards realizing a 4-terminal GaAs-Ge mechanical dual junction stack and eventually a triple-junction InGaP-GaAs-Ge mechanical stack is currently ongoing.