I have been making and drinking sun tea for years, so this information surprised me. It's my understanding that making sun tea with black tea is less risky than doing so with herbs or decaf. The caffeine inhibits the microbes flourishing for about three hours.
Our best bet is to make refrigerator tea or simply make tea the old fashioned way with boiling water. However it's made, don't let it set at room temperature for more than a few hours. Refrigeration is key.