Você só precisará de visto se planeja visitar Istambul. Se você estiver hospedado na área de trânsito, então você não precisa de visto. A partir da página de FAQ do Ministério dos Negócios Estrangeiros da Turquia :
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 (Ministry/Turkish Representations).
No entanto, se você quiser visitar Istambul, então precisará de um visto :
Bangladeshi nationals holding diplomatic and official/service passport are exempted from visa for their travels up to 90 days. Ordinary passport holders are required to have visa. These passport holders with a valid Schengen or OECD member's visa or residence permit may get their single entry e-Visas valid for one month e-Visas via the website www.evisa.gov.tr, provided that they meet certain conditions.