Nanostructured antireflective coating for gallium arsenide solar cells

<p class="p1"><span class="s1">A Spanish research team demonstrated a broadband antireflective coating for gallium arsenide solar cells. Based on thermally oxidized gallium nanoparticles, the nanostructured coating reduced reflectance by 30% across the solar spectrum, and increased solar cell performance by 10%.</span></p><p>Researchers led by a team at Spain's <a href="https://www.pv-magazine.com/2025/04/11/determining-mismatch-losses-in-bifacial-pv-based-on-single-axis-trackers/" rel="noopener" target="_blank">Technical University of Madrid (<span>ISOM-UPM</span>)</a> have demonstrated a broadband antireflective coating (ARC) for gallium arsenide-based solar cells. The nanostructured coating was based on thermally oxidized gallium nanoparticles.</p>
<p>“Unlike conventional plasmonic metallic nanoparticles that can cause parasitic absorption, the fully oxidized gallium oxide nanoparticles (GaxOy-NPs) preserve the nanoparticle morphology and act as non-resonant, all-dielectric ARCs,” Sergio Catalán Gómez, corresponding author, told <strong>pv magazine</strong>.</p>
<p>“These GaxOy-NPs reduce reflectance by about 30% across the solar spectrum and improve solar cell external quantum efficiency and short-circuit current density by approximately 10%,” he stated.</p>
<p>The research, which is detailed in “<a href="https://doi.org/10.1016/j.optmat.2025.117696">Thermally Oxidized Gallium Nanoparticles as Broadband Antireflective Coatings for GaAs Solar Cells</a>,” published in <em>Optical Materials</em>, builds on earlier work with Ga-NPs but with a focus on oxidation and dielectric nanoparticle layer technology for antireflective functionality. It offers &#8220;new insights into “scalable oxide nanostructured coatings for photovoltaics,” according to Catalán Gómez.</p>
<p>“While plasmonic Ga-NPs have attractive light-scattering properties, their practical use in GaAs solar cells is limited because plasmonic resonances can overlap with the cell absorption spectrum, causing losses,” explained Catalán Gómez.</p>
<p>The search for an alternative with the “morphological advantages of these NPs but without plasmonic losses” resulted in the choice of gallium oxide. Gallium oxide emerged as an &#8220;excellent&#8221; candidate due to its refractive index and wide bandgap.</p>
<p>The group fabricated the GaAs solar cells in-house using standard photolithography and metallization procedures to ensure the study reflected performance on devices it controlled throughout the fabrication and coating processes.</p>
<p>“We then directly deposited Ga-NPs onto the front surface of these custom-fabricated cells and performed the oxidation treatment to form the GaxOy-NPs,” said Catalán Gómez. The process enabled precise optical property tuning of both size and surface coverage.</p>
<p>The results indicated that when the “initial NP radius remains below ∼30 nm&#8221;, then there was complete oxidation without compromising structural integrity. It was confirmed by microscopy analysis.</p>
<p>Simulations based on atomic force microscopy (AFM) measurements accurately reproduced the experimental spectra, validating the optical model. “The resulting GaxOᵧ-NPs exhibit a uniform, smooth morphology essential for predictable optical behavior and robust antireflective performance,” said the researchers.</p>
<p>“When implemented on GaAs solar cells, these coatings yield reproducible enhancements in external quantum efficiency and short-circuit current density, with average improvements of around 10 %,” they noted, adding that control experiments confirmed that the gains are” solely due to the presence of these oxidized NPs.”</p>
<p>Further discussing the results, the group stressed how the plasmon-free technology is compatible with standard device processing and that the graded-index optical coating shows “great promise” for III-V photovoltaic applications.</p>
<p>Researchers from Universidad de Cádiz participated in the study.</p>
<p>Of interest for future research is optimizing antireflective performance and making larger stable GaxOy-NPs. Additionally, integrating these coatings into other III-V multijunction solar cells and long-term stability studies under operational conditions are priorities for future work, according to Catalán Gómez.</p>