High-efficiency GaInP∕GaAs∕InGaAs triple-junction solar cells grown inverted with a metamorphic bottom junction

The authors demonstrate a thin, Ge-free III–V semiconductor triple-junction solar cell device structure that achieved 33.8%, 30.6%, and 38.9% efficiencies under the standard $1\text{sun}$ global spectrum, space spectrum, and concentrated direct spectrum at $81\text{suns}$ , respectively. The device consists of $1.8\mathrm{eV}$ ${\mathrm{Ga}}_{0.5}{\mathrm{In}}_{0.5}\mathrm{P}$ , $1.4\mathrm{eV}$ GaAs, and $1.0\mathrm{eV}$ ${\mathrm{In}}_{0.3}{\mathrm{Ga}}_{0.7}\mathrm{As}$ $p\text{-}n$ junctions grown monolithically in an inverted configuration on GaAs substrates by organometallic vapor phase epitaxy. The lattice-mismatched ${\mathrm{In}}_{0.3}{\mathrm{Ga}}_{0.7}\mathrm{As}$ junction was grown last on a graded ${\mathrm{Ga}}_x{\mathrm{In}}_{1-x}\mathrm{P}$ buffer. The substrate was removed after the structure was mounted to a structural “handle.” The current-matched, series-connected junctions produced a total open-circuit voltage over $2.95\mathrm{V}$ at $1\text{sun}$ .