Should I bleach my deck or just power wash it?
"Green mold" on a deck is almost certainly algae, not mold.

A bleach-water mixture (not straight bleach - perhaps 1 cup per gallon at the most, considerably less might be sufficient) will kill the algae and make it much easier to remove. 

I happen to know someone who (evidently) is a big fan of pressure-washers and not much of a fan of bleach or scrub brushes. They'll go 3 days with the pressure washer to do what one day with bleach and a scrub-brush would do more effectively, and the traces of algae that are left behind recolonize in short order. You can be that guy, or not...