NOVELTY - Photovoltaic device comprises p-type amorphous silicon layer (106) formed on a substrate (102); barrier layer (108) formed on the p-type amorphous silicon layer, where barrier layer is a carbon doped amorphous silicon layer; and intrinsic type amorphous silicon layer (110) formed on the barrier layer.    USE - Photovoltaic device i.e. solar cell device (claimed), i.e. single junction thin-film solar cell (100) or tandem junction thin-film solar cell.    ADVANTAGE - The barrier layer serves as a cap layer and/or interface barrier layer that prevents the dopants, such as boron dopants, or other impurities from the underlying p-type amorphous silicon layer from diffusing or penetrating into the nearby adjacent layers during the subsequent high temperature deposition process, reducing the likelihood of contaminating or damaging the film layers and the solar cell devices formed on the substrate. The carbon element formed in the barrier layer can efficiently strengthen the silicon bonding microstructures with stronger silicon-carbon bonds, providing a robust bonding network and thus preventing impurities and dopants from diffusion to the adjacent film layers. It acts as trap sites to capture boron elements to slow down or eliminate boron diffusion. The barrier layer is formed as a carbon rich film so as to be stable enough against the thermal or plasma damage that may be generated during the subsequent manufacture process. The carbon rich barrier layer provides structural flexibility to offset minor structure changes from the underlying p-type layer, so that the addition of the barrier layer in the solar cell structure can only produces negligible series resistance increase. The amorphous silicon layer is used in solar cell junction with low film optical bandgap and broad wavelength absorption range along with barrier layer that can generate high current, increasing the photoelectric conversion efficiency and device performance of the photovoltaic solar cell as compared to conventional methods.    DETAILED DESCRIPTION - An INDEPENDENT CLAIM is included for formation of solar cell device.    DESCRIPTION OF DRAWING(S) - The drawing is a schematic side-view of single junction thin-film solar cell.    Single junction thin-film solar cell (100)    Substrate (102)    P-type amorphous silicon layer (106)    Barrier layer (108)    Intrinsic type amorphous silicon layer (110)