Amorphous silicon schottky barrier solar cells

Abstract

By the evaporation of polycrystalline silicon in high vacuum ($P_b\lesssim1\times10^{-7}$ Torr) amorphous silicon films were prepared. The hydrogenation of those samples were by DC discharge of hydrogen gas after evaporation and by using Pd film as an agent for diffusing atomic hydrogens into amorphous silicon films. The samples prepared by using Pd film showed wide optical band gap, but the resistivities were not so large. Thus, the possibility of hydrogenation of amorphous silicon films by the later method is yet to be confirmed and still remains as a hopeful candidate for a new method of hydrogenation. On the other hand, the sample prepared by DC discharge showed high resistivities and good Schottky barrier junctions were obtained from these samples. This confirms that amorphous silicon films can be hydrogenated effectively by DC discharge after evaporation of amorphous silicon films. Amorphous silicon - metal Schottky barrier solar cells were fabricated by the deposition of amorphous silicon films ($\sim$1 $\mu$m) on epitaxially grown $n^+$ -n type crystalline silicon wafers ($\sim$250 $\mu$m) and followed by hydrogenation. Those samples showed good diode characteristics. The sample using Pt showed $V_{oc}=0.32$ V under the illumination of 10 mW/$cm^2$ and the efficiency of that sample was 0.06\%. Jsc - Voc curves showed straight lines as expected and $\beta$ values ranged from 1.5 to 2. J - V curves however deviated from the conventional diode characteristics. The result could be explained qualitatively by assuming double Schottky barrier formation between amorphous and crystalline silicon.