The original Star Wars movies are great movies with great story telling
but I don't consider them to be sci-fi. Adventure, drama, sure but just
because a story takes place in space that doesn't make it science fiction
nor does science fiction need to take place in space.
If you're looking for more movies like The Martian, movies that start with
a seed from scientific knowledge, theory, or at least hypotheses and then
extrapolate into fiction try searching for "hard scifi", generally that
leans a bit more toward the sci and less toward the fi.
Though, it's all still subjective.