Single-crystal Cu(In,Ga)Se2 solar cells grown on GaAs substrates

Single-crystal Cu(In,Ga)Se-2 (GIGS) solar cells were produced with techniques developed for high-efficiency polycrystalline GIGS solar cells. The GIGS layers of a lattice match with GaAs were grown on GaAs(001) substrates by co-evaporation. The presence of a single-crystal GIGS layer without dislocations was confirmed by transmission electron microscopy. Alkaline metal incorporations were achieved by doping and postdeposition treatments. Ga grading structures were fabricated by two-layer deposition with different Ga contents. The Ga grading significantly increased the fill factor and open-circuit voltage. The best efficiency of 20% was achieved after heat-light soaking. (C) 2018 The Japan Society of Applied Physics