By way of example, we are researching the GaInNAs material system as well as ternary and quaternary III-V semiconductor aluminum alloys for monolithically grown five- and six-junction solar cells. We also work with strain-compensated multiple quantum wells to achieve improved current matching in multi-junction cells. To enable the metamorphic growth of layers – where materials with differing lattice constants are grown – we design suitable buffer layers that form substrates for high quality solar cell structures. Such structures are used, for example, to grow multi-junction solar cells on silicon.
The wafer bonding process, in which semiconductor layers are bonded with one another, is also an important technology-driven area that enables us to combine different semiconductors, such as GaSb, GaAs, InP, Si and Ge. In December 2014, we achieved the world record efficiency of 46% with a wafer-bonded, four-junction solar cell. This record cell was developed in collaboration with the partners Soitec, CEA-Leti and Helmholtz-Zentrum Berlin.
A unique application of III-V photovoltaic cells is their use under monochromatic radiation from LEDs or lasers. Extremely high conversion efficiencies can be achieved here, meaning that such photovoltaic cells are often used in wireless power supply systems.