Light-trapping structures based on low-melting point metals for thin-film solar cells

In this article, a new way based on low-melting-point metals is provided to fabricate light-trapping structures. Three classic metals, Al, Bi and Sn, are utilized to introduce textured topography. The fabrication technologies are quite simple that traditional evaporation is used here. The obtained textured Bi and Sn coatings are oxidized in air to be Bi₂O₃ and SnO₂. Root-mean-roughness of over 100nm can be obtained, 120nm, 150nm and 142nm for Al, Bi₂O₃ and SnO₂, respectively. Angle resolved scattering (ARS) of the coatings dependence on light scattering in air is compared and all the three coatings can scatter the incident light into large angles effectively. This indicates good light absorption in the subsequently deposited absorber layer. The three coatings are used as back reflectors and different silicon thickness from 300nm to 1200nm are sputtered on. The amorphous silicon is recrystallized by Cu induce crystallization. The reflectivity of the samples is tested by a spectrometer with an integrating sphere and average reflectivity (R_a) in the wavelength region from 400nm to 1100nm is discussed to reveal the light-trapping efficiency. The results presents that with only 300nm thick silicon layer, the R_a can be limited to 14% for the SnO₂ coating. The R_a of Bi₂O₃ coated structure changes little when the silicon thickness changes between 480nm and 1200nm, and with only 480nm thick silicon layer, the R_a can be limited to 12%. For the textured Al coating, an optimal silicon thickness exists as 840nm and the Ra can be limited to nearly 10% at this point. We believe that the technologies are suitable for thin film solar cells for mass production.