You want white shades not black. A lot of modern glass is thermal blocking. It has a coating to reflect Infrared light. With black curtains, the sunlight hits the curtain and is absorbed. The curtain then re-radiates it as infrared. This spreads it around the room, since the window blocks it. With white, the light reflects off, and back out the window. This keeps more heat out.
For best effect, you want to use Mylar foil. I personally found the mylar bubble wrap wall insulation worked extremely well. It’s quite stiff, so easy to cut and handle. I used suction cups to hold it to the window. The outside would be the absolute best, but it still works extremely well on the inside.