why ibook doesn't want to open anymore after ios9.1

Hello,

After i updated my iphone 5S for ios9.1, I noticed the ibooks app doesn't want to open anymore. When I click on it, it crashes automatically, nothing open. The thing is, I use ibook everyday, a lot of pdf files are "gone" since I can't open the app neither synchronize it with itunes. What can I do to have an ibook app that can finally work ?
Thank you