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HL: Fachverband Halbleiterphysik

HL 12: Photovoltaic

HL 12.2: Vortrag

Montag, 25. Februar 2008, 14:15–14:30, EW 202

Monolithic III-V- tandem solar cell lattice matched to InP(100) with a GaInAs/GaAsSb tunnel junction — •Nadine Szabó, Ulf Seidel, Erol Sagol, Klaus Schwarzburg, and Thomas Hannappel — Hahn-Meitner-Institut, Glienicker Str. 100, Berlin

At present, III-V triple junction (3J) solar cells are achieving the highest conversion efficiencies (η=40.7%) worldwide. These cells are grown slightly lattice mismatched to Ge(100) and are containing three absorber layers: Ge, GaInAs and GaInP. Even higher efficiencies are possible if more than 3 subcells were used. To obtain this, one can replace the Ge bottom cell by a GaInAsP/GaInAs tandem cell grown lattice matched to InP. The combination of these low band gap subcells with an established GaAs/GaInP tandem solar cell can be realised by mechanical stacking. The GaAs/GaInP// GaInAsP/GaInAs 4J tandem solar cell has a theoretical conversion efficiency limit of 61% (500 suns), which is clearly higher than the limit of the current world record 3J solar cell (49%). The serial connection of the two subcells of our tandem cell was realised by a tunnel junction. This tunnel junction was composed of a n-GaInAs and a p-GaAsSb layer. Depending on the preparation of the n-GaInAs layer, the p-GaAsSb layer was grown either on III-rich or on V-rich surfaces. Whereas the growth of the GaAsSb layer on a III-rich surface led to a sharper interface. Sun simulator measurements have been performed in order to investigate the influence of the different preparation methods on the cell efficiencies.