Epitaxial lift-off GaAs/AlGaAs solar cells for flexible devices

Abstract

Rapid development of wearable electronics, mobile devices and autonomous vehicles has generated a new demand for highly efficient, yet flexible, low-weight SCs. The already existing photovoltaic technology uses GaAs layers with a thickness of several microns due to their flexibility and high absorption coefficient. Promising approach here is flexible single-junction SCs based on GaAs heterostructures with thickness of several micrometers and lifted off the growth substrate. To obtain flexible SCs structures, the methods of separating GaAs/AlGaAs nanostructures from the growth substrate using wet-etched release layer within an improved post-growth processing. The implementation of the work involves numerical calculation of the optical and electronic properties of SCs to search for the optimal design of nanostructures (morphology and composition of layers, doping profile) for subsequent epitaxial synthesis. Thus, the approaches used in the implementation of the work will make it possible to achieve progress at each of the steps to create highly efficient flexible SCs based on GaAs/AlGaAs nanoheterostructures and release layer.
Numerical calculation was made to determine the optimal design of a GaAs/AlGaAs based thin film lift-off SCs and AlInP sacrificial layer, corresponding to a maximum energy conversion efficiency. Based on numerical calculation GaAs/AlGaAs nanoheterostructure SCs were synthesized by molecular beam epitaxy on 2-inch diameter (100) GaAs wafers. AlInP epitaxial layer lattice-matched with GaAs were used as the material for the wide-gap window and the rear potential barrier, which also act as a release layer during liquid etching. After growth, first the n-side AuGe (300 nm) metal rear contact was deposited by vacuum evaporation and annealed at 400°C to ensure low contact resistivity. Next, the front side of the cell structure was accessible for the deposition of the p-side Cr/Au (5/100 nm) grid contact. Contact layer was removed by wet etching in citric acid. After that, the I-V characteristics were measured, as well as the efficiency (under AM1.5 spectrum) and external quantum efficiency.
In this work, numerical calculation of the lift-off solar cell with an AlInP core layer was carried out. The GaAs/AlGaAs nanoheterostructure was synthesized by molecular beam epitaxy. The main photo-electrical characteristics of the solar cell were measured.

The reported study was funded by RSF, project number 22-79-10286 (research in the field of epitaxial growth)
D M Mitin thanks the council on grants of the president of the Russian Federation, project number MK-3031.2021.1.2 (metal contacts deposition, I-V measurement)

Speaker

Dmitry Mitin
Alferov University
Russia

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