We have investigated the characteristics of amorphous silicon (a-Si) thin-film solar cell by inserting barrier layer. The conversion efficiency of a-Si thin-film solar cells on graphite substrate shows nearly zero because of the surface roughness of the graphite substrate. To enhance the performance of solar cells, the surface morphology of the back side were modified by changing the barrier layer on graphite. The surface roughness of graphite substrate with the barrier layer grown by plasma enhanced chemical vapor deposition (PECVD) reduced from ~2 um to ~75 nm. In this study, the combination of the barrier layer on graphite substrate is important to increase solar cell efficiency. We achieved ~ 7.8% cell efficiency for an a-Si thin-film solar cell on graphite substrate with SiNx/SiOx stack barrier layer.