Nanoscale piezoelectric (PZ) energy harvesters, or nanogenerators (NGs), are vital for next-generation autonomous devices as they can directly convert small-scale vibrations, such as blood flow and body movements, into electrical energy. Scavenging power from ubiquitous vibrations in this way offers an attractive route to supersede fixed power sources such as batteries that need constant replacing/recharging. In particular, epidermal or implantable PZ NGs could revolutionize wearable electronics and healthcare monitoring. The associated elastic environments require not only flexibility of the NG, but also stretchability in order for it to remain operational. Current NGs are rarely functional without being coupled to rigid or, at best, flexible substrates, due to the lack of proper methodology for fabrication of both stretchable electrodes as well as stretchable high-performance PZ nanomaterials, that together make up PZ NGs. Thus, the Action has aimed to (i) develop micro/ nano-patterned electrode fabrication techniques based on electronic printing on flexible/stretchable substrates, (ii) develop polymer-based PZ materials with tailored elastic properties to satisfy stretchability and flexibility criteria, marking a departure from traditional PZ materials that are ceramic in nature and hence stiff and brittle, and (iii) study the efficiency of the stretchable NGs developed, based on simulations and direct measurements of energy harvesting (EH) performance in elastic environments.
In this Action, the Researcher has firstly successfully designed and fabricated freestanding stretchable electrodes, based on aerosol jet printing technology, conductive nanoparticle inks and polymeric inks. The electrode was geometrically structured to be stretchable, providing up to 180 % extension with resistance being changed by less than 3 times. The as-fabricated device could potentially be applied as a strain sensor under large deformation. Multi-layered of electrodes can be fabricated over one stretchable structure, making it applicable in on-skin touching sensing, integrated stretchable circuit, or stretchable humidity sensing. The Researcher has also conducted reviewing on polymer-based PZ NGs, simulation performing of the as-fabricated electrodes being applied in power generating, as well as attempt of integrating the nanogenerator with the electrode. Due to time limitation, the fully integrated stretchable PZ NG was not accomplished due to the as-fabricated stretchable electrodes not being structurally preferable in driving PZ material, based on some simulation and experimental results. Overall, the achieved objectives in this Action have addressed fabrication techniques for stretchable electrodes and their conducting or sensing applications in biological and other extreme environments that involve large scale deformation, as well as to provide a potential way, which still needs more research, to integrate polymeric PZ materials for stretchable energy harvesters.
