I picked up a whole whack load of bananas for $4 (on clearance) at the produce store, aiming to make banana chips.
I've made 2 attempts already. Both times, I sliced the bananas then soaked the slices in a solution of water and citric acid powder for 10 minutes. The slices were then laid out on cheese cloth-covered oven racks.
The first time, I clearly baked the banana slices for too long... probably too high (8 hours @ 225F). The were mostly charred, but a few were still yellow and had achieved the desired crunch. The second time, I over-compensated by cutting thinner slices, then cooking at a lower temperature for less time (170 for 2 hours). They were not charred this time. However, they came out soft rather than crunchy.
In both cases they tasted quite good. The drying intensifies banana's flavor, while the citric acid adds a bit of sweetness and a bit of sourness.