As in one solar mass of telescope or just a telescope as wide as the sun's radius?
The latter seems achievable, if tricky.
It uses the sun's gravity as a gravitational lens. You fly a normal sized telescope to the focal point. The theoretical resolution is pretty mindblowing, we'd be able to make out oceans and continents on exoplanets.
The main problem seems to be getting to the focal point, which is 500+ AUs from the Earth.