No, you don't need a transit visa as long as you stay in the international area, according to Turkey's e-visa portal
Do I have to obtain a visa if I do not leave the international transit
No. You do not have to get a visa if you are not going to
leave the international transit area.
More of the same from the Turkish Ministry of Foreign Affairs
Question: I will be flying to Europe. I know that our aircraft will
land in İstanbul. I am not planning to leave the transit lounge. Do I
need to get transit visa?
Answer: If you will not leave the transit lounge at the airport you
are not required to have transit visa. Otherwise, you have to make
visa application to the nearest Turkish Representation. Contact
information of the said missions can be reached through www.mfa.gov.tr