Semiconductor nanowire (NW) solar cells with a single p-n junction have exhibited efficiency comparable to that of their planar counterparts with a substantial reduction in material consumption. Tandem geometry is a path toward the fabrication of devices with even higher efficiencies, for which a key step is the fabrication of tunnel (Esaki) diodes within NWs with the correct diameter, pitch, and material combination for maximized efficiency. InP/GaInP and GaInP/InP NW tunnel diodes with band gap combinations corresponding to high-efficiency solar energy harvesting were fabricated and their electrical characteristics and material properties were compared. Four different configurations, with respect to material composition and doping, were investigated. The NW arrays were grown with metal–organic vapor-phase epitaxy from Au particles by use of nano-imprint lithography, metal evaporation and lift-off. Electrical measurements showed that the NWs behave as tunnel diodes in both InP (bottom)/GaInP (top) and GaInP (bottom)/InP (top) configurations, exhibiting a maximum peak current density of 25 A/cm2, and maximum peak to valley current ratio of 2.5 at room temperature. The realization of NW tunnel diodes in both InP/GaInP and GaInP/InP configurations represent an opportunity for the use of NW tandem solar cells, whose efficiency is independent of the growth order of the different materials, increasing the flexibility regarding dopant incorporation polarity.
Keywordsnanowire tunnel diode InP GaInP tandem junction solar cell
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We thank Dr. Enrique Barrigón and Dr. Pyry Kivisaari for helpful discussions during the course of this work. We also thank Dr. Ingvar Åberg and co-workers at SolVoltaics AB, for helping with EBIC measurements. The research leading to these results was performed within NanoLund at Lund University and supported by the Crafoord Foundation, the Swedish Research Council, the Swedish Energy Agency, the Coordination for the Improvement of Higher Education Personnel (CAPES-Brazil), the European Union’s Horizon 2020 research and innovation programme under grant agreement No. 641023 (Nano-Tandem), and the People Programme (Marie Curie Actions) of the European Union’s Seventh Framework Programme (FP7-People- 2013-ITN) under REA grant agreement No. 608153, PhD4Energy. This publication reflects only the author’s views and the funding agency is not responsible for any use that may be made of the information it contains.
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