Enhanced performance of GaInP/GaAs/Ge solar cells under high concentration through Pd/Ge/Ti/Pd/Al grid metallization

Abstract Series resistance is the key limiting factor that constrains the electrical performance of solar cells under ultra‐high concentration. Typically, the most critical component of the series resistance is that stemming from the front contact, and therefore, the formation of front metal grids with low metal–semiconductor specific contact resistance and low metal sheet resistance is vital for high concentrator solar cells. Consequently, in this study, a novel Pd/Ge/Ti/Pd/Al metal stack has been proposed and implemented on a GaInP/GaAs/Ge triple junction solar cell. This system exhibits low metal resistivity due to the middle Ti/Pd barrier layer hindering the diffusion and contamination between the GaAs semiconductor and top conductive metal layer, and very low specific contact resistance because of the Pd/Ge layer forming an interfacial layer with the GaAs cap which increases the electron tunneling probability. As a result, the fill factor of the solar cell remains almost constant and close to 90% in the 250× to 1500× range, while efficiency keeps on increasing even at the maximum concentration measured of 1500×. Its performance and cost‐effectiveness make this contact a compelling solution to extend solar cell operation in the ultra‐high concentration regime.