English: Schematic of a Peltier device. On top and bottom insulating heat spreaders are used and assumed to be connected to heat and cold reservoirs, respectively. They are shown semi-transparent. P- and n-type thermoelectric materials are stacked electrically in series and thermally in parallel. Depending on whether a current source or a resistive device is connected to the electrical connections, this can work as a Peltier element or a thermoelectric generator.