Broadband antireflection TiO₂-SiO₂ stack coatings with refractive-index-grade structure and their applications to Cu(In,Ga)Se ₂ solar cells

Introduction of broadband antireflection coatings (ARCs) is a promising method to enhance efficiency of solar cells. In this paper, the TiO ₂-SiO₂ stack coatings with refractive-index-grade structure are proposed and have been successfully fabricated via sol-gel dip-coating technique. The structure, morphology, optical properties and wettability of TiO₂-SiO₂ stack coatings were systemically investigated. The broadband antireflection performance is improved over the solar spectrum with increase of solar transmittance by 7.80% and maximum transmittance of 99.16% at 550 nm on glass slide substrates. The responding reflectance is largely reduced and the minimum values in visible and near-infrared regions are 0.40% and 0.05%, respectively. By introducing broadband ARCs, the efficiency of Cu(In,Ga)Se₂ solar cells is increased from 11.20% to 12.15%, which reveals superiority and importance of TiO₂-SiO₂ stack coating as an outstanding antireflection material, having high potential for practical applications.