There can be no free will in heaven.
This conclusion can only be arrived at if we establish and agree on two factors:
1) Sin is a product of free will - without free will we would not have the option to sin. If we were to place this within the bible we need only look at the story of the Garden of Eden. Adam was created, he was deceived and chose to eat of the fruit of knowledge of good and evil, without that choice (free will), he would not have been able to sin against God. So we can conclude that as long as free will exists so does sin.
2) Heaven is a place free from sin - Rev 21:18,17 and 15 all describe that heaven is a place free from sinners and sin, Rev 15 - "But nothing unclean will ever enter it, nor anyone who does what is detestable or false, but only those who are written in the Lamb’s book of life.", I need only quote from scripture to prove this point.
So we can therefore make the overall assumption that heaven is a place without free will, upon entering into the realm of Heaven you enter a puppet show where you live as an automaton under the control of God.
However, a further question can then be raised. How did the devil become the devil.
Within the bible we learn that the devil was an angel within heaven who sinned against God and so was cast into hell. So this juxtaposes what we have just established. The idea of the creation of the devil and the inability to sin in heaven are mutually exclusive. So are we then only left to draw the conclusion that one or both of them are false? Either you can sin in heaven (going against what the bible says) or you cannot sin (meaning that the devil was never created as the angel never had the ability to sin against god). Or the easier answer to arrive at; the heaven described within the bible does not exist.