Multi-junction solar cells by Intermetallic Bonding and interconnect of Dissimilar Materials: GaAs/Si

We present a novel, low temperature approach to multijunction solar cell fabrication combining the high efficiency multi-junction concept with the low cost of thin film technology in one solar cell structure. The intermetallic bonding approach presented is based on joining indium metal which has been deposited on the metal contact grid of the respective solar cells. This approach avoids the problems of lattice mismatch and tunnel junction limitations, connecting solar cells of potentially any material with patterned contacts. No measurable increase in resistance has been measured between bonded materials. This method allows the independent development of each cell technology for use in multijunction solar cells. This technique can be applied to any commercial off-the-shelf solar cells, if available. A GaAs/Si multijunction solar cell bonded using this approach is demonstrated. The silicon cell is off-the-shelf with textured surface and commercial metal contacts. This is integrated with an in-house grown thin film GaAs cell. The GaAs/Si device is demonstrated in both two and three terminal configurations.