c-Si/n-ZnO-based flexible solar cells with silica nanoparticles as a light trapping metamaterial

Herein, we report the fabrication of flexible solar cells based on a crystalline p-Si/n-ZnO heterostructure for the first time. An enhancement of ∼52% in the base efficiency was achieved by the application of spherical SiO₂ nanoparticles as light trapping structures on the top. The use of ZnO not only offers a facile route of synthesis, but also provides an additional advantage of large band bending, leading to notable open circuit voltage and formation of an intermediate ultra-thin barrier layer of Zn₂SiO₄ for minimized carrier recombination. The spherical silica nanoparticles act as nanoresonators, causing absorption hot-spots in the thin silicon absorber, along with the capability of providing wide-angle light-collection. Simulation showed, for the higher angle of incidence, that the silica nanoparticles have the ability to bend light on the same side of the normal to the incident wave-front, thereby acting as a negative index metamaterial (NIM). The flexibility and cost-effectiveness of this device can make it important for the next-generation photovoltaics and roll-to-roll electronics.