Upvote:2
Yes, your husband would need a visa if he wants to exit the transit area. As a Nigerian citizen holding a valid Schengen resident permit, he is eligible to apply for one month e-Visa via the website www.evisa.gov.tr
Nigeria: Ordinary, official/service passport holders are required to have visa to enter Turkey. These passport holders with a valid Schengen members or USA, UK, Ireland 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.
Source: http://www.mfa.gov.tr/visa-information-for-foreigners.en.mfa