Yes it can be done outside in a spot that catches morning sun ..... BUT depending on what organisms are present in the water you use, you may get growth of unwanted organisms like stringy algae.
Every biofilm is unique. The organisms that grow in it depend on complex interaction between the organisms that are present and the environment. For example, if you have moss in the jar then there will be a different suite of organisms present than if you use plastic plates as the substrate. Even two jars set up in exactly the same way beside each other will have substantially different biofilm communities. Similarly if you use fertiliser to boost growth of the biofilm, some species will do better than others and possibly take over. This is a common problem in marine aquaculture because you want crustose coralline algae and diatoms rather than turfing algae, which you can do by managing the amount of light and the water flow over the plates. because of this - growing biofilm cannot be done by recipe. You have to just do it and adjust what you are doing based on your results. If you get too much stringy algae, place the biofilm in a shadier spot. If you dont get much growth, try adding fertiliser (tiny amount) and/or more light.
There is some annecdotal evidence that exposure to light makes shrimp have better colouration, and therefore would indicate better health. Secondly growth of autotrophic organisms in biofilms ( algae, diatoms ect. that photosynthesise, and are arguably the most nutritious organisms eaten by shrimp) relies on light being present. Although you would be adding biofilm for the shrimp to eat, I think it would be better to also encourage growth of biofilm in the aquarium itself as well by ensuring adequate lighting. And to be adequate, you dont need much light at all. For example, I only run an Aqua Pro Z for 4 hours over my zebra tank, which provides a nice green coating over the rocks in their tanks, plus of course ambient light from being inside a house and dappled light through a window on the other side of the room. When I ran the Aqua Pro Z for 6-8 hours I tended to get growth of stingy algae which the zebs did not eat.