Thank you for using the Jiskha Homework Help Forum. Here are some sites on that literature:
1. (Wikipedia): http://en.wikipedia.org/wiki/Heart_of_Darkness
2. (Spark Notes): http://www.sparknotes.com/lit/heart
3. (Study Guide): http://www.gradesaver.com/classicnotes/titles/heartofdarkness/
4. (Book Notes): http://www.bookrags.com/notes/hod/
There is no one answer for this, I think. This book is in "story within a story" format. The inner story is clearly first person, but you'll need to decide about the outer (or frame) story.