Self-compensated insulating ZnO-based piezoelectric nanogenerators

Remarkable enhancement of piezoelectric power output from a nanogenerator (NG) based on a zinc oxide (ZnO) thin film is achieved via native defect control. A large number of unintentionally induced point defects that act as n-type carriers in ZnO have a strong influence on screening the piezoelectric potential into a piezoelectric NG. Here, additional oxygen molecules bombarded into ZnO lead to oxygen-rich conditions, and the n-type conductivity of ZnO is decreased dramatically. The acceptor-type point defects such as zinc vacancies created during the deposition process trap n-type carriers occurring from donor-type point defects through a self-compensation mechanism. This unique insulating-type ZnO thin film-based NGs (IZ-NGs) generates output voltage around 1.5 V that is over ten times higher than that of an n-type ZnO thin film-based NG (around 0.1 V). In addition, it is found that the power output performance of the IZ-NG can be further increased by hybridizing with a p-type polymer (poly(3-hexylthiophene-2,5-diyl):phenyl-C₆₁-butyric acid methyl ester) via surface free carrier neutralization.