A proposal for broadband wavelength conversion using four-wave mixing is presented based on a slot waveguide with silicon nanocrystals (Si-nc's) as the optical nonlinear material. The dispersion of the waveguide is engineered to realize a flat dispersion as well as a small effective mode area for better nonlinear interaction by optimizing the waveguide dimensions. The conversion performance is synthetically analyzed and numerical results show that a bandwidth of over 400 nm and an efficiency of -2.38 dB can be achieved using a pump power of 150 mW in a 4 mm long Si-nc slot waveguide with slot width of 50 nm, slab width of 310 nm, and height of 305 nm.