Dresden 2009 – wissenschaftliches Programm

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HL: Fachverband Halbleiterphysik

HL 5: Photovoltaic

HL 5.5: Vortrag

Montag, 23. März 2009, 11:30–11:45, POT 151

Performance of InGaAsP/InGaAs tandem solar cells with an InGaAs/GaAsSb tunnel junction — •Erol Sagol, Nadine Szabo, Ulf Seidel, Christian Höhn, Klaus Schwarzburg, and Thomas Hannappel — Helmholtz-Zentrum Berlin, Glienicker Str. 100, 14109 Berlin-Germany

Three types of state-of-the-art III-V triple-junction solar cells have already surpassed the 40% efficiency mark, despite having non-optimized band gaps. But still considerably higher efficiencies can be achieved with a four-junction configuration, which has optimized band gaps around 1.9, 1.4, 1.0 and 0.7 eV. This can be realized with a mechanically stacked GaAs-based GaInP/GaAs tandem and an InP-based InGaAsP/InGaAs tandem cell. For this purpose, we grew InGaAsP/InGaAs tandem solar cells lattice-matched to InP by MOVPE. The InGaAs bottom cell (0.73 eV) and the InGaAsP top cell (1.03 eV) were connected with a tunnel junction, which was composed of highly doped n-InGaAs and p-GaAsSb layers. In order to evaluate the performance of the tunnel junction, separate devices were grown without the photoactive layers. High current densities of several thousand A/cm2 were achieved already in the bias regime of several 100 mV. Hence, voltage losses in the tunnel diode should not be of concern for the solar cell even under extreme concentration ratios (> 1000 suns). Our results show that the contribution of such a low band gap InGaAsP/InGaAs tandem bottom cell, reaching efficiencies above 10% under GaAs, is considerably higher than a conventional germanium subcell.