C60/a-C superlattice structures for solar cell applications

C₆₀/amorphous carbon (a-C) superlattice structures were fabricated by shutter controlled molecular beam deposition. A-C layers were transformed from C₆₀ by nitrogen ion bombardment. The dark and photo conductivity of C₆₀/a-C superlattice structures were measured by gap-cell structure. The resulted films show high resistivity, and the photosensitivity ratio ranged from 9∼16. It is thought that such low photosensitivity is caused by high defect density of 2.7×10²¹ cm^-3 in the a-C layers. Use of hydrogen plasma in C₆₀ amorphization process, instead of nitrogen, reduces the spin defect density in two orders of magnitude. Hydrogen atoms effectively reduce the defect density of a-C films by etching the weak carbon bond structures and/or passivating the dangling bonds.