Wafer-bonded Four-junction Solar Cell with 47.6% Conversion Efficiency for High Concentrating Photovoltaics

Photonic power converters (PPCs) attract more and more attention as they enable galvanically isolated optical power transmission. In most applications, conversion efficiency is the key metric for PPCs and a remarkable efficiency of 68.9% was achieved by leveraging Fabry-Pérot resonances in a GaAs PPC using a back surface reflector. In this work, we extend the idea of resonant absorption towards strong grating coupled guided mode resonances. We show ultrathin PPCs with photonic structures etched into the semiconductor material and with a planarized metal mirror to minimize parasitic losses. We show EQE and I-V measurements of such structured devices in comparison to devices with a planar mirror for three different absorber thicknesses. We show an EQE of 60% at the band gap of GaAs (870nm) for a cell without antireflection coating and an only 345 nm thin absorber. The EQE of a reference device with planar mirror is limited to 18% at 870 nm. Finally, the results are compared to wave optical modeling.