Multilayer Antireflection Coatings for Cover Glass on Silicon Solar Modules

Abstract

The cover glass on solar modules provides protection for the underlying solar cells but also leads to two forms of power loss: reflection losses and soiling losses. In this work, we report on the design of a broadband multilayer antireflection (MAR) coating designed for use with silicon modules and its advantages over commercial porous SiO <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$_{2}$</tex-math></inline-formula> sol-gel coatings. The six-layer antireflection coating comprising SiO <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$_{2}$</tex-math></inline-formula> and ZrO <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$_{2}$</tex-math></inline-formula> has then been deposited on glass using high-rate pulsed dc magnetron sputtering. The reflection losses are reduced by 2.4% absolute compared with uncoated glass, whereas commercial SiO <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$_{2}$</tex-math></inline-formula> coatings reduce reflection by 2.2%. The increased light reaching the solar cell improves the short-circuit current density ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">J</i> <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$_{{{sc}}}$</tex-math></inline-formula> ) and spectral response, which increases the conversion efficiency from 17.1% to 17.5%, a relative increase of 2.34%. The coating is environmentally robust and abrasion resistant, whereas porous SiO <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$_{2}$</tex-math></inline-formula> AR coatings are susceptible to abrasion damage and water ingress. The sputtering process used to fabricate the MAR coating is used for high throughput applications by most major glass manufacturers. We also explore the addition of a thin hydrophobic layer of refractive index <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">n</i> = 1.35 to the outer surface of the MAR coating. Addition of the hydrophobic layer increases the water contact angle of the MAR coating from 7 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$^{\circ }$</tex-math></inline-formula> to 114 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$^{\circ }$</tex-math></inline-formula> , with a significant increase in antisoiling properties without compromising AR performance. MAR coatings offer improved light transmission and improved durability over commercial porous SiO <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$_{2}$</tex-math></inline-formula> sol-gel AR coatings.