Fig. 1

Previously reported flexible energy harvesting devices. Nanogenerators based piezoelectric materials such as (a) ZnO NW (reproduced from ref. [12, 14, 15] with permission, American Chemical Society and Wiley–VCH). b PVDF polymer (reproduced from ref. [16, 18] with permission, American Chemical Society) c Perovskite ceramic thin film (reproduced from ref. [19, 21, 22] with permission, American Chemical Society and Royal Society of Chemistry)