Detailed comparison of transparent front contacts for thin film silicon solar cells

In this contribution we compare the optical, electronic and surface morphological properties of various textured transparent conducting oxides (TCO) based on zinc oxide and fluorine doped tin oxide. Since the TCO material properties tend to be interrelated, comparison of such films is a rather complex exercise. The TCO films were characterised by atomic force microscopy, scanning electron microscopy, spectrophotometry, angle resolved scattering, four point probe and Hall Effect measurements. Thereafter, an attempt was made to correlate the TCO material properties with the corresponding current-voltage characteristics and quantum efficiency in actual solar cells. It was found that the solar cells were more sensitive to changes in the optical properties of the TCO substrates than to those in the sheet resistance. Based on these results, we recommend that when optimising TCO films for thin film silicon production, the first priority should be to obtain the highest transmittance possible and then to tune the electrical properties accordingly.