Scalable hierarchical wood/ZnO nanohybrids for efficient mechanical energy conversion

•In situ synthesis of hierarchical 3D array of multilayered ZnO inside wood.•Highly charged wood enables multilayered ZnO synthesis without seeding.•Wood/ZnO composites are efficient for piezoelectric mechanical energy conversion.•The output voltage is 1.5 V with output current of 2.91 nA and power density of 2.91 nW/cm2.