Hey There: the most efficient way to keep the heat out are either replacing the windows with glass that suits your area code or having exterior shutters/shades installed. This way, the heat does not penetrate into the room.

If this is not an option, you have to tackle the problem from the inside with honeycomb/cellular shades for example. They can open bottom-up and top-down to manage light and privacy while the double layer of fabric helps with the heat.

One last note: do not do a film - this will be a permanent job and in the winter when you need the sun, it is still blocked.

Where is the home? I would also look into some of the solar rejection films.

I had the same problem with my upstairs. I did several things, each one of which help. Cellular shades on all the windows. Bottom up/ top down are a nice way to keep view open before about 3 pm. For the hottest room I put up double-lined drapes from Plow and Hearth that extend about 5” beyond sides of windows. By 3 pm they are drawn. Then I had a/c tech out to go over entire system. He adjusted some levers on ducts in basement, advised changing filters more often. My home is only 10 years old so it has excellent insulation but attic was over 120 degrees in summer. I had a roofing company Install a new , higher profile ridge vent that draws much more of the heat out. That dropped the temperatures in my attic by over 10 degrees. Cost was $500. Altogether these chances reduces evening temperatures in upstairs by 8 degrees with thermostat at same setting as prior to changes,

Cellular shades are great, just be careful if you are in a colder region because they can cause (or make worse) issues with condensation.