Optical and passivating properties of sol-gel derived silica and titania coatings on textured monocrystalline silicon

In standard solar cell fabrication, silicon nitride is applied to the front surface by plasma enhanced chemical vapor deposition. The layer serves as an antireflective coating and provides passivation, but is costly to produce. An interesting alternative of making thin films is the sol-gel technique. The process is simple, cheap and low-temperature. In the present study, silica and titania sol-gel coatings were applied to textured and polished monocrystalline silicon wafers and subsequently annealed in a furnace. On polished wafers, the solar averaged reflectance was decreased from 0.37 to 0.11 with a titania layer and to 0.25 with a silica layer. The deviation in reflectance did not translate onto textured wafers. The reflectances of these wafers were decreased from about 0.13 to about 0.08 independently of coating type. The layers were not found to passivate the surface. The layers are promising in terms of reflectance, but to improve passivation properties new approaches are necessary.