1. A device for converting thermal energy into electrical energy, comprising a first layer and a second layer of thermally conductive material, an intermediate layer of polymer material arranged between the first and second layers and having a thermal conductivity lower than the first and second layers, wherein a plurality of channels in which a colloidal suspension of active particles is contained is arranged inside the intermediate layer, the colloidal suspension being capable of flowing along each channel of the plurality of channels as a result of a temperature gradient applied between the first layer and the second layer, and a plurality of pick-up elements arranged along said channels and configured to extract electrostatic force or electromotive force induced as a response to a flow of the colloidal suspension as a result of at least one among a pyroelectric effect, a triboelectric effect, and thermomagnetic advection, wherein each channel of the plurality of channels forms a closed loop and comprises an outgoing branch and a return branch extending as an asymmetrical helix, each of the outgoing and return branches comprising a plurality of turns, each of which has diametrically opposed portions adjacent to the first layer and to the second layer, respectively.