We report on the fabrication and measurement of ultrathin a-Si solar cells with plasmonic back contacts composed of nanopattern dendritic/shrub-like Ag nanostructures that exhibit enhanced short circuit densities compared cells with flat back contacts. The morphology of the Ag nanostructure can be well controlled by the reaction time. When the proposed structure was used in the solar cell. The back-reflector of solar cell can be well designed by various Ag nanostructures and periods. A one-dimension shrub-like Ag nanostructure with spacing of 600 nm, exhibited a 14 % increase in short-circuit current density and a 20% increase in energy conversion efficiency are observed. This study indicates that the dendritic/shrub-like Ag nanostructure can be applied as a enhancing conversion configuration for ultrathin a-Si solar cells.