I don't have first hand knowledge but since I am going in May, I investigated. From Fodors:
Obtaining visa at Ataturk Airport
"Just to clarify the procedure:
You submit your passport with visa fee, which for US passport is US$20. You can only pay in dollar bills (no change given)or in euro (15 euro). You cannot pay in Turkish lira, TC or credit/debit card. Sticker visa is affixed and passport returned. You than go to passport control and obtain an entry stamp."
Ian