Silicon paste prepared by boron doped Si nanoparticles and organic carriers is used as the source. The Si wafers from the standard process of solar cells are used as the substrate. The Si paste is fully screen-printed on the preprocessed Si rear surface and dried, and then a homogenous B-doped Si cladding layer is formed by picosecond laser. During the process, B diffuses into the substrate. The structure of Si cladding layer and doping performance of B element are observed by laser scanning microscope, scanning electron microscope, and secondary ion mass spectroscopy. The results show that the Si cladding layer formed by picosecond laser is uniform and dense without cracks and voids. The highest B concentration in the cladding layer is about 3×1019 atom/cm3, and B is doped into the Si substrate for the depth of 0.5-1 μm. Cells with an average efficiency of 20.3% are fabricated on China Sunergy′s production line.