A display panel and a display device are disclosed and belong to the field of display technology. The display panel comprises a first substrate and a second substrate opposite to each other, a liquid crystal layer, a first electrode, and a second electrode between the first substrate and the second substrate, a waveguide layer between the first substrate and the liquid crystal layer, and a plurality of grating units which are combined with the liquid crystal layer and disposed in a same layer as the liquid crystal layer; wherein the first electrode and the second electrode are configured to adjust a refractive index of the liquid crystal layer by changing voltages applied thereto; and a coupling efficiency at which light is coupled out of the waveguide layer is determined according to a difference between a refractive index of the grating units and the refractive index of the liquid crystal layer.