  Nano-scaled metallic or dielectric structures may provide various ways to
trap light into thin-film solar cells for improving the conversion efficiency.
In most schemes, the textured active layers are involved into light trapping
structures that can provide perfect optical benefits but also bring undesirable
degradation of electrical performance. Here we propose a novel approach to
design high-performance thin-film solar cells. In our strategy, a flat active
layer is adopted for avoiding electrical degradation, and an optimization
algorithm is applied to seek for an optimized light trapping structure for the
best optical benefit. As an example, we show that the efficiency of a flat
a-Si:H thin-film solar cell can be promoted close to the certified highest
value. It is also pointed out that, by choosing appropriate dielectric
materials with high refractive index (>3) and high transmissivity in wavelength
region of 350nm-800nm, the conversion efficiency of solar cells can be further
enhanced.
