Nonlinear current–voltage characteristics based on semiconductor nanowire networks enable a new concept in thermoelectric device optimization

Thermoelectric (TE) devices that produce electric power from heat are driven by a temperature gradient ( $$\Delta T = T_{\text{hot}} - T_{\text{cold}}$$ , T hot: hot side temperature, T cold: cold side temperature) with respect to the average temperature (T). While the resistance of TE devices changes as $$\Delta T$$ and/or T change, the current–voltage (I–V) characteristics have consistently been shown to remain linear, which clips generated electric power (P gen) within the given open-circuit voltage (V OC) and short-circuit current (I SC). This P gen clipping is altered when an appropriate nonlinearity is introduced to the I–V characteristics—increasing P gen. By analogy, photovoltaic cells with a large fill factor exhibit nonlinear I–V characteristics. In this paper, the concept of a unique TE device with nonlinear I–V characteristics is proposed and experimentally demonstrated. A single TE device with nonlinear I–V characteristics is fabricated by combining indium phosphide (InP) and silicon (Si) semiconductor nanowire networks. These TE devices show P gen that is more than 25 times larger than those of comparable devices with linear I–V characteristics. The plausible causes of the nonlinear I–V characteristics are discussed. The demonstrated concept suggests that there exists a new pathway to increase P gen of TE devices made of semiconductors.