Printable lightweight polymer-based energy harvesting systems: materials, processes, and applications

Polymer-based flexible energy harvesting systems based on several physical phenomena such as piezo-, pyro-, thermo-, and triboelectric effects have become increasingly relevant for self-powered nanogenerator devices to, as an example, replace batteries in remote or inaccessible places, or develop self-powered sensors. Tailored properties of the materials, combined with advanced manufacturing technologies, will increase the intrinsic properties and improve integration into devices of the energy harvesters’, making them even more attractive to provide energy for applications concerning the increased need for sensors for the digitalization of society and economy. The selection and manipulation of the polymer as a host matrix and filler with appropriated properties is critical for maximizing the output power of the flexible devices, together with the printing technique and the device geometry. Printing techniques allow custom design, improved integration, small to large scale, and low-cost devices with improved sustainability. In this review, the main characteristics of the most used printing techniques and polymer-based materials for the different flexible energy harvesting technologies are provided. The most used physical phenomena are the piezo- and triboelectric ones, based on PVDF for piezoelectric systems, and silicone for triboelectric device applications, mostly based on the contact-separation method, and printed by 3D technique to generate energy. Thermoelectric devices are mainly developed by inkjet printing and are based on bismuth materials. Pyroelectric printed devices are the least explored, relying mostly on screen printing and electroactive PVDF. Finally, hybrid systems combining two different effects will maximize the energy generated.