Both Samsung NX300M and Olympus PEN-F have 20.0 MP resolution sensors but Samsung NX300M's sensor is APS-C (23.5 x 15.7 mm ) and Olympus PEN-F's sensor is Four Thirds (17.3 x 13 mm ).
Since Samsung NX300M'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 Olympus PEN-F.
Below you can see the NX300M and PEN-F sensor size comparison.
As seen above, Samsung NX300M has a 1.6x Larger sensor area than Olympus PEN-F. 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.