Flexible a-Si:H Solar Cells with Spontaneously Formed Parabolic Nanostructures on a Hexagonal-Pyramid Reflector

Flexible amorphous silicon (a-Si:H) solar cells with high photoconversion efficiency (PCE) are demonstrated by embedding hexagonal pyramid nanostructures below a Ag/indium tin oxide (ITO) reflector. The nanostructures constructed by nanoimprint lithography using soft materials allow the top ITO electrode to spontaneously form parabolic nanostructures. Nanoimprint lithography using soft materials is simple, and is conducted at low temperature. The resulting structure has excellent durability under repeated bending, and thus, flexible nanostructures are successfully constructed on flexible a-Si:H solar cells on plastic film. The nanoimprinted pyramid back reflector provides a high angular light scattering with haze reflectance >98% throughout the visible spectrum. The spontaneously formed parabolic nanostructure on the top surface of the a-Si:H solar cells both reduces reflection and scatters incident light into the absorber layer, thereby elongating the optical path length. As a result, the nanopatterned a-Si:H solar cells, fabricated on polyethersulfone (PES) film, exhibit excellent mechanical flexibility and PCE increased by 48% compared with devices on a flat substrate.