In today's Hall H panel at Comic-Con, Warner Bros. just revealed that the Green Lantern's solo movie will be called Green Lantern Corps, which is due out in 2020.
So the next Green Lantern movie is actually going to be "Green Lantern Corps," according to the title that just flashed on the screen— Ben Fritz (@benfritz) July 11, 2015
That title has been rumored for weeks, and suggests that Hal Jordan's first outing in the new DC Universe will be bigger than his last one. In DC canon, the Green Lantern Corps is an intergalactic police force that defends sectors of the known universe. They collectively call on the power of the Central Power Battery using their famous rings, which allows them to harness the green energy of will to create constructs like weapons and allow them to fly through space.
Apart from Jordan, the Corps has included famous Lanterns like John Stewart, Kyle Rayner, and even Sinestro. There's still no word on casting yet, but it's safe to assume Warner Bros. is going to start looking for serious talent to fill its ranks.