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HL: Fachverband Halbleiterphysik

HL 17: Poster I

HL 17.34: Poster

Montag, 25. Februar 2008, 16:30–19:00, Poster D

InGaAsP/InGaAs tandem solar cells for higher conversion efficiencies in multi-junction solar cells — •Ulf Seidel, Erol Sagol, Nadine Szabó, Klaus Schwarzburg, and Thomas Hannappel — Hahn-Meitner-Institut, Glienicker Str. 100, 14109 Berlin, Germany

III-V multi-junction solar cells are currently the most efficient photovoltaic devices. The present world record multi-junction solar cells (eta > 40%) contain three absorber layers: Ge, GaInAs and InGaP. Our idea is to replace the bottom Ge subcell by a more efficient InGaAsP/InGaAs tandem solar cell with low band gaps. The preparation of materials and solar cells with higher band gaps (> 1.4 eV) on the lattice constant of GaAs is already well-established, in contrast to tandem solar cells with lower band gap materials grown on InP. However, low band gaps, in particular an 1 eV absorber, are desired to raise the theoretical efficiency limit of multi junction solar cells. Here, InGaAsP/InGaAs tandem solar cells with low band gaps (1.03 eV, 0.73 eV) were grown monolithically and lattice-matched on InP(100). The serial connection of the two subcells was realized by a tunnel diode, including n-doped InGaAs and p-doped GaAsSb layers. In-house measured conversion efficiencies were much higher than the efficiency that was achieved with a single-junction Germanium subcell. The combination of the GaAs/InGaP tandem with higher band gaps and our low band gap tandem prepared on different substrates with different lattice constants can now be realized by mechanical stacking and also via splitting of the solar spectrum.