Strictly speaking it's not the Peltier effect, but the Seebeck effect. One is the inverse of the other; Peltier junctions produce a temperature gradient when current is passed through, and Seebeck ones generate a current when exposed to a temperature gradient.
I think for the most part you can actually run either type in either mode, but the design and materials differ for optimal efficiency across the 2 modes.
I think for the most part you can actually run either type in either mode, but the design and materials differ for optimal efficiency across the 2 modes.