Design of novel TiO2–SiO2 core–shell helical nanostructured anti-reflective coatings on Cu(In,Ga)Se2 solar cells with enhanced power conversion efficiency

Abstract

Introducing an anti-reflective coating (ARC) is the last step of fabricating Cu(In,Ga)Se₂ solar cells with enhanced photo-generated current by reducing the reflectance of visible light. The use of nanostructures in ARC has been intensively investigated because this can prolong the optical path length by a scattering effect or by the formation of a refractive index gradient. Herein, we proposed the use of TiO₂ helical nanostructures using glancing angle deposition (GLAD), and then synthesized SiO₂ surrounding the helical nanostructures to further decrease the reflectance by producing a refractive index gradient. The optimized values of TiO₂ and SiO₂ thicknesses are 150 nm and 3 nm determined by the finite-difference time-domain (FDTD) simulation on Cu(In,Ga)Se₂ solar cells. The suppression of reflectance led to enhanced light absorption across a broad wavelength range, and boosted the J_SC from 20.66 to 22.51 mA cm⁻², resulting in improved power conversion efficiency (PCE) from 6.32 to 7.00% after applying the TiO₂–SiO₂ core–shell nanostructures as the ARC. This 10.75% PCE enhancement suggests that the novel TiO₂–SiO₂ core–shell nanostructures have great potential as ARC for Cu(In,Ga)Se₂ solar cells, and it would be beneficial for development in the photovoltaic field in both research and applications.