What is your purpose for researching.I had to research such because of the work that I was doing and things that were happening.I would talk to a confessor first and tell them your purpose.If they give you the green light then I would devote equal amount of prayer as to the reading and make sure your in a state of Grace.I would not recommend any of the books on the market.Any exorcists I know have never written a book.They don’t even tell people they are exercists.I would recommend Blessed Anne Catherine Emmerich.She gives a pretty good history and the bad guys against the good guys.
What about that priest who is that well known exocist by the last name of Father Amonth? He wrote a book I believe.