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 (sigma(rms)) 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 (pc-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 (J(sc)) for an a-Si:H solar cell and an 11.9% for mu c-Si:H were observed in the solar cells on the nanotextured back reflectors, with little reduction in fill factor (FF) and open circuit voltage (V-oc). Due to the increase of the J(sc) by the improved light absorption at the long wavelengths, the conversion efficiency (eta) of the a-Si:H and pc-Si:H solar cells increased from 5.59% to 7.60% and from 4.31% to 4.64%, respectively. (C) 2012 Elsevier B.V. All rights reserved.