Engineering the reciprocal space for ultrathin GaAs solar cells

TL;DR

This paper introduces a method to design quasirandom photonic structures that enhance light absorption in ultrathin GaAs solar cells, significantly increasing photocurrent and maintaining stability under angle and structural variations.

Contribution

It presents a novel design approach to evolve photonic crystals into quasirandom structures for improved broadband light trapping in ultrathin solar cells.

Findings

Quasirandom structures increase photocurrent from 16.1 to 25.3 mA/cm².

Enhanced absorption spectrum shows a transition from discrete peaks to a continuum.

Photocurrent enhancement remains stable under angle and structural variations.

Abstract

III-V solar cells dominate the high efficiency charts, but with significantly higher cost than other solar cells. Ultrathin III-V solar cells can exhibit lower production costs and immunity to short carrier diffusion lengths caused by radiation damage, dislocations, or native defects. Nevertheless, solving the incomplete optical absorption of sub-micron layers presents a challenge for light-trapping structures. Simple photonic crystals have high diffractive efficiencies, which are excellent for narrow-band applications. Random structures a broadband response instead but suffer from low diffraction efficiencies. Quasirandom (hyperuniform) structures lie in between providing high diffractive efficiency over a target wavelength range, broader than simple photonic crystals, but narrower than a random structure. In this work, we present a design method to evolve a simple photonic crystal into a quasirandom structure by modifying the spatial-Fourier space in a controlled manner. We apply these structures to an ultrathin GaAs solar cell of only 100 nm. We predict a photocurrent for the tested quasirandom structure of 25.3 mA/cm$^2$, while a planar structure would be limited to 16.1 mA/cm$^2$. The modified spatial-Fourier space in the quasirandom structure increases the amount of resonances, with a progression from discrete number of peaks to a continuum in the absorption. The enhancement in photocurrent is stable under angle variations because of this continuum. We also explore the robustness against changes in the real-space distribution of the quasirandom structures using different numerical seeds, simulating variations in a self-assembly method.