If you have to do it in the sun, do it in the morning. What you want to avoid here is heat. Heat works against you. Wet your window with the sponge side, then flip to the white scrub pad side, and scrub the window. You'll feel rough patches when it's still not clean.
Diapers work well.
The trick for leaving no streaks with the squeegee is to place the dry rubber blade on a dry window. Place the squeegee at the top of the window in that dry strip. Pull down smoothly. Dry your squeegee blade with a cloth between each sweep. Take a dry, clean cloth and run it with your finger down each side of the window and across the bottom to clean and dry the edges.