Fabrication of InGaAsP Solar Cells for Concentrator Applications

Transfer printing is an emerging technology for the mechanical stacking of III-V multijunction solar cells, yielding ultra high efficiency devices under concentration while avoiding existing epitaxial growth limitations. This commercial technique allows for energy harvesting of the entire solar spectrum through combinations of devices grown on GaAs, InP and GaSb substrates. In this paper, individual single junction materials outlined as transfer printing candidates in an InP-based tandem were investigated to optimize a fabrication process and to study electrical device performance. InGaAsP single junction solar cells grown by MOCVD at compositions of In 0.9 Ga 0.1 As 0.21 P 0.79 (corresponding to a 1.2 eV band gap) and In 0.76 Ga 0.24 As 0.52 P 0.48 (1.0 eV band gap) were demonstrated. Process optimization, including particular mesa isolation challenges, and device characterization are discussed.