Tribovoltaic Energy Harvesting with ZnO Semiconductor–Metal Interfaces: The Role of an Al2O3 Tunnel Barrier Layer

Harvesting low-grade motion to convert to electricity has emerged as a critical technology for powering autonomous electronic devices. In particular, the tribovoltaic effect arising from lateral friction across a semiconductor–metal interface has demonstrated great promise for low power devices, with the phenomenon producing large currents but quite low voltages. Zinc oxide (ZnO) is one of the most commonly studied electromechanical materials; however, to date, this semiconductor has been relatively unstudied for tribovoltaic devices. Herein, we demonstrate the fabrication and performance of thin films from ZnO prepared by atomic layer deposition correlated to film thickness and surface coating. The ZnO thin films demonstrate a tribovoltaic current of 0.8 nA in contact with an Au probe, corresponding to a current density of 21 A cm^–2. The mechanism of the tribovoltaic effect in ZnO was probed by the addition of a 2 nm aluminum oxide layer, which blocks hole transport and acts as a tunnel barrier layer, reducing the theoretical amount of charge recombination and limiting induced (hot) electron transfer from metal to ZnO. This work provides a key report in the use of ZnO for the tribovoltaic effect, offering a pathway to engineering multilayered heterostructures for either preventing or enhancing tribovoltaic charging.