I have "How to dry food" By Deanna Delong and she states that commercially dried bananas are flavored and fried to get that super crispness, not treated with chemical (so they say) No pretreatment is needed according to the book and they should dry at 150* in about 2 hours. And she recommends only using ripe but still very firm bananas.
The book states you can dip in lemon juice or lemon juice and honey and be rolled in nuts, seeds, coconut before drying also. The book states they do not do well trying to dry in the sun they ferment first, and take longer to dry in humid weather. Hope that helps, I am just getting into dehydrating and had to buy a book I was lost.