Presentation held at The 20th International Conference on Metal Organic Vapor Phase Epitaxy (ICMOVPE XX), Stuttgart, Germany, 10.07.2022-14.07.2022

Concentrating photovoltaics (CPV) is the photovoltaics technology that yields the highest efficiency by far. Modules with energy conversion efficiencies above 43 % have been demonstrated. Furthermore, energy payback times in Europe for such a technology are below one year and the technology has a proven long-term stability in e.g. power generation farms in South Africa. Since the terrestrial PV market is extremely cost competitive, the main developments nowadays are geared towards cost reduction. In the case of CPV, the area related costs are dominating. Thus, increasing cell efficiency and concentration factor show the largest leverage for cost reduction. In this work, we focused on increasing the solar cell efficiency of a Ga0.51In0.49P/Al0.03Ga0.97As//Ga0.15In0.85As0.65P0.35/Ga0.47In0.53As four junction solar cell. The cell consists of an upright grown bottom tandem cell structure, lattice matched to InP, and an inverted grown top structure, lattice matched to GaAs. The two structures were grown using MOVPE with an AIXTRON 2800G4-TM reactor and joined by direct waferbonding at SOITEC in France. A four-layer anti-reflection coating was applied after cell processing. Here, we present the current development status of this quadruple-junction solar cell. Careful subcell absorber material characterisation and optimisation using XRD, spectrally and time-resolved PL, and AFM along with precise MOVPE process control allowed to maximise the cell voltage and obtain current matching between the four subcells. The device reached a power conversion efficiency of 47.6 %, illuminated with the AM1.5d spectrum at 665-fold concentration in a calibrated measurement at the Fraunhofer Callab. This is the highest solar cell efficiency reported up to date.