No Charging but Protection: Lifetime Prolongation of Spontaneously‐polarized Electrets for Energy Harvesting Applications

With no need for separate charging processes, spontaneously‐polarized electrets are gaining increased attention, particularly in energy harvesting. However, vulnerability to environmental factors, like illumination, moisture, or mechanical contact may cause a rapid loss of surface potential, rendering their suitability for real‐world applications uncertain. To enhance their stability—focusing on a wind energy harvesting application—a bilayer protection is proposed, consisting of zinc sulfide and polystyrene thin films. A bare 1,3,5‐Tris(1‐phenyl‐1H‐benzo[d]imidazol‐2‐yl)benzene (TPBi) sample loses 35% of initial surface potential after 16 h of light exposure, and nearly the entire of that upon water contact or mechanical impact with a grounded counter‐electrode. Implementing a bilayer protection comprising a 50 nm‐thick zinc sulfide film and an 11.8 μm‐thick titanium dioxide‐doped polystyrene layer, despite introducing fabrication‐related losses, reduces surface potential photodegradation to 3.5% of initial value. Moreover, 14.4 μm‐thick polystyrene layers doped with zinc oxide and titanium dioxide nanoparticles best protect TPBi, so that almost no surface potential decay is observed after 2‐min full‐surface water contact, and after 100 000 impacts with grounded counter‐electrode, respectively. The effects of the aforementioned protections on Tris(8‐hydroxyquinoline)aluminum (Alq 3 ) are comparable to those on TPBi against water contact and mechanical impact, but significantly less pronounced under light.