Lead-free piezoelectric nanowire-nanocellulose hybrids for flexible energy harvesters

• Applicant: Dr. Lutz Geelhaar, since 11/2023
• Subject Area: Experimental Condensed Matter Physics ; Synthesis and Properties of Functional Materials
• Term: since 2021
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 490935200

It is highly desirable to make future low-power electronic devices sustainable, maintenance-free, and self-powered (free of batteries). A solution resides in the use of nanowire-based piezoelectric energy harvesters that can turn ambient mechanical energy into usable electrical power. The mechanical flexibility of these nanodevice makes their integration on soft surfaces straightforward, which is highly relevant for biomedical applications. This prospect calls for the development of new piezoelectric materials showing enhanced performances in terms of stretchability and conformability. In addition, these materials should show biocompatibility, biodegradability and a high electromechanical efficiency. In NanoFlex, we will synthesize a novel inorganic-organic flexible hybrid film for piezoelectric energy harvesting. We will explore the combination of three unique nanomaterials: highly piezoelectric nitride nanowires, plant-based nanocelluloses, and graphene. The rationale for the choice of materials is to minimize the environmental footprint of the device, while ensuring high flexibility and maintaining an appreciable electromechanical efficiency. We will explore various options for boosting the piezoelectric performances of the nitride nanowires. We will start with AlN nanowires grown by molecular beam epitaxy and alloy them with rare-earth elements like Scandium (Sc). The lattice frustration induced by the presence of Sc should result in an extraordinary enhancement of the piezoelectric coefficients. We will further tailor the piezo-response of the nitride nanowires by strain engineering, to benefit from nonlinearities in the piezoelectric coefficients and to profit from flexoelectricity. Our results will help identifying generic routes to optimize the piezoelectric properties of nitride and other wurtzite materials like ZnO. We aim at replacing eco-unfavourable components of conventional flexible devices (e.g., synthetic polymers, plastic substrates and metallic contacts) by green materials. Hence, we will use nanocelluloses as an encapsulating matrix for the nanowires and nanopapers as a flexible substrate. We will also use graphene as electrical contact to couple the generated signal to the external circuit. Our goal is to produce a usable inorganic-organic piezoelectric film having a total thickness down to 10 µm. The functionality of the hybrid films as a flexible piezoelectric energy harvester will be evaluated with respect to ZnO and other lead-free competitors. We will systematically analyze the overall device performances (piezo-output, flexibility, and robustness), and correlate them with the properties of each components characterized at the nanoscale and with choices made in the process optimization and in the device structure.

• DFG Programme: Research Grants
• International Connection: France
• Cooperation Partners: Frank Dahlem; Rudeesun Songmuang
• Ehemaliger Antragsteller: Dr. Thomas Auzelle, until 11/2023