Pushing the Boundaries of Photovoltaic Light to Electricity Conversion: A GaAs Based Photonic Power Converter with 68.9% Efficiency

Abstract

We present recent results achieved in the field of photonic power conversion, i.e. monochromatic light to electricity conversion, using photovoltaic cells. Based on a thin film processing approach we leverage photon recycling and optical resonance effects with a GaAs/AlGaAs rear-heterojunction photovoltaic cell. A back reflector yields increased effective minority carrier lifetime and, as a consequence, an increase in voltage. Optical resonance in the microcavity yields high absorptance close to bandgap despite weak absorptivity. Hence, high current is reached while thermalization losses are minimized. Maximal spectral response SR=0.653 A/W is measured at 858 nm. At this wavelength, thermalization losses diminish to only 21 meV per photon or 1.5%rel. Based on the calibrated spectral response combined with light I-V measurements under broad band and monochromatic light, we determine a maximum equivalent monochromatic power conversion efficiency at 858 nm of 68.9%±2.8%.

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