Nanoscale Teflon coated surface nano-roughened Si solar cells with Teflon thickness dependent efficiency and hydrophobicity

By employing the SiN and Teflon-like films as surface anti-reflective coatings, the sub-wavelength nano-pillar roughened poly-crystalline Si photovoltaic solar cells are characterized and compared. With 22nm-thick Teflon-like film coating, the bared Si PV cell shows filling factor and energy conversion efficiency of 0.70 and 10.89%, respectively, which are comparable with a standard cell employing standard SiN anti-reflective film to coat the bared Si PV cell. The water contact angle increases from 55° to 92.6° as the Teflon-like film thickness enlarges to 200 nm or larger, whereas the conversion efficiency of the Telfon-like film coated Si PV cell slightly degrades by 1.4% as compared to that of the bared Si PV cell. Lengthening the nano-roughened structure further results in a decreasing reflectance from 30% to 5% and an enhanced scattering to degrade the transmittance from 15% to 3% in visible wavelength region. The nano-pillar surface not only induces the multiple scattering to enhance the Haze and to reduce surface reflectance, but also shadows the incident light to reach the inner cell.