  Nano-scaled dielectric and metallic structures are popular light tapping
structures in thin-film solar cells. However, a large parasitic absorption in
those structures is unavoidable. Most schemes based on such structures also
involve the textured active layers that may bring undesirable degradation of
the material quality. Here we propose a novel and cheap light trapping
structure based on the prism structured SiO2 for thin-film solar cells, and a
flat active layer is introduced purposefully. Such a light trapping structure
is imposed by the geometrical shape optimization to gain the best optical
benefit. By examining our scheme, it is disclosed that the conversion
efficiency of the flat a-Si:H thin-film solar cell can be promoted to exceed
the currently certified highest value. As the cost of SiO2-based light trapping
structure is much cheaper and easier to fabricate than other materials, this
proposal would have essential impact and wide applications in thin-film solar
cells.
