Effect of nanotextured back reflectors on light trapping in flexible silicon thin-film solar cells

Nanotextured Ag back reflectors were used to enhance the short-circuit current of flexible silicon thin-film solar cells with an n-i-p configuration by means of optical confinement. A nanotextured topography with a root-mean-square (σrms) surface roughness of 88.0 nm was successfully induced by abnormal grain growth of Ag films, which was controlled by varying the deposition temperature and film thickness in a direct current (dc) magnetron sputtering process. Effective light scattering of the long wavelengths over 600 nm was achieved on the nano-textured Ag back reflectors, resulting in enhanced absorption of weakly absorbing, long-wavelength light in the hydrogenated amorphous silicon (a-Si:H) and microcrystalline silicon (μc-Si:H) thin-film solar cells. Compared with similar reference cells on flat back reflectors, a 34.4% increase in the short-circuit current density (Jsc) for an a-Si:H solar cell and an 11.9% for μc-Si:H were observed in the solar cells on the nanotextured back reflectors, with little reduction in fill factor (FF) and open circuit voltage (Voc). Due to the increase of the Jsc by the improved light absorption at the long wavelengths, the conversion efficiency (η) of the a-Si:H and μc-Si:H solar cells increased from 5.59% to 7.60% and from 4.31% to 4.64%, respectively.