Executive Summary :
Objective: To design and fabricate contact-separation mode TENG structures; To develop lead-free, flexible piezoelectric materials for PENG structure; Integration of PENG and TENG for hybrid power generation; Design and development of electronic interface for self-powered operation
Summary: Energy harvesters for tapping mechanical energy are of immense interest as it is the most wasted form of energy in modern civilization. A variety of approaches have been illustrated for converting mechanical energy into useful electrical energy by various phenomena such as electromagnetic, magnetostriction, electrowetting, piezoelectricity and triboelectricity. Among the mechanical energy harvesters, triboelectric nanogenerators (TENG) are self-sufficient power sources which effectively convert mechanical energy into electricity based on the coupling between triboelectric effect and electrostatic induction. This clean, portable mechanical energy harvester has many advantages such as large output power, low cost, simple production and high conversion efficiency. TENG can cater the power demands of fast growing flexible electronics industry including wearable electronics, bendable displays and electronic skin applications. Various surface modification techniques have been applied for enhancing the power output of TENG such as etching, plasma treatment, printing of special structures etc. But this will add to the overall cost, decrease in life time and increase the complexity of fabrication for large-scale production.
On the other hand, piezoelectric nanogenerators (PENG) work on the principle of electricity generation when subjected to mechanical stress or vibration. In a typical PENG, two electrodes with balanced Fermi levels on a piezoelectric material are subjected to an external strain, which creates a piezo potential difference between the internal and external Fermi levels. PENGs have shown high efficiency at low frequencies, enable wide choice of materials and are light weight in comparison to electromagnetic generators (EMGs). However, there are several burning issues to overcome for practical exploration of PENG in the self-powered electronics. These handicaps include low power output, poor mechanical durability and lastly, high cost of production from a mass production perspective. Interestingly, some of these issues, especially the low power output of PENGs, can be complemented by TENGs. Thus, it would be highly desirable to scavenge both types of energy using a single nano-electric cell, which can largely help the scaling trends of miniaturization.
Amalgamating the advantages of both TENG and PENG, we propose a coupled energy harvesting device; Piezo/Tribo-hybrid-electric nanogenerator for application in next-generation self-powered electronics. The hybrid generators can deliver high power output as a resultant of the coupling between high output current PENG with high output voltage TENG. Also, the nano/micro-structuring of TENG surfaces can be avoided for getting higher power output and thereby reduces the overall cost and enhances the life of device. The proposed hybrid nanogenerator is composed of two triboelectrically active materials, which are placed far apart in triboelectric series, among which one is having piezoelectricity too. We aim to develop a flexible, lead-free piezoelectric material for integrating with TENG for enhanced output power. The device operates in a contact-separation mode, in which TENG and PENG will be producing electrical output simultaneously in a single press and release cycle. The electrical output of TENG-PENG system will be combined through a custom designed electronic circuit. Thus, the tapping of mechanical energy will be maximized through the coupled nanogenerator system. Further, the present project also plans to address some of the burning issues that delimit the output performances of hybrid nanogenerators, such as the driving frequency, phase difference and mismatched impedance.