Exposure to sunlight is the best way to kill moss. Moss needs shady, moist conditions to survive and it quickly dies when the sun's rays shine on it. However, bleach is a close second. It will effectively kill moss within a matter of hours. And, it can help keep moss from growing back. Moss can't live on inorganic surfaces alone. It needs a thin layer of dirt or other organic material to gain a foothold, and a periodic bleach scrubbing will quickly get rid of that.
Mix a 30% household bleach and water solution into a large bucket or spray bottle (depending on how large the mossy area is).
Pour or spray the bleach solution onto the mossy area.
Leave the bleach solution on the moss for 1 hour.
Hose the bleach solution off.
Scrub the area with a scrub brush and the bleach solution. This will effectively remove any remaining dead moss and clean off any of the organic matter that it needs to grow. Periodically scrub the area with the 20% bleach solution even if you don't see any moss growing to make sure that it doesn't come back.