Both Leica V-Lux 20 and Leica C have 12.0 MP resolution sensors but Leica V-Lux 20's sensor is 1/2.3-inch (6.08 x 4.56 mm ) and Leica C's sensor is 1/1.7-inch (7.44 x 5.58 mm ).
Since Leica C's has a larger sensor area with the same resolution, this means that it also has a larger pixel area hence better light collecting capacity for a given aperture compared to Leica V-Lux 20.
Below you can see the V-Lux 20 and C sensor size comparison.
As seen above, Leica C has a 1.5x Larger sensor area than Leica V-Lux 20. Larger sensors give photographer more control on the depth of field and blurry background compared to smaller sensor when shot in same focal length and aperture.