Periodic Reporting for period 1 - UNIFY (Unification of the best piezoelectric and photovoltaic properties in a single photoferroelectric material)
Reporting period: 2022-06-01 to 2024-11-30
This project aims to revolutionize the field of micro-energy harvesting for ubiquitous wireless sensor networks by creating a single material that exhibits both excellent piezoelectric (PE) and efficient photovoltaic (PV) properties. The PE effect is one of the fundamental electromechanical coupling functions extensively utilized in sensors, actuators and transducers for various industrial sectors. The PV effect generates green electricity from solar energy. At present, materials with robust PE and efficient PV properties belong to distinct families. The project’s objective is to bridge this divide by developing new photoferroelectric materials that have the potential to unify the strong PE and efficient PV effects. The challenges include, for instance, not all high-quality ferroelectric materials exhibit strong PE responses. In addition, robust PE materials have wide bandgaps, rendering them incapable of absorbing visible light necessary for an efficient PV effect. Furthermore, the efficiency of current photoferroelectric materials is significantly lower than conventional solar cells. To address these challenges, this project will conduct a comprehensive study on the role of different chemical elements as dopants in parent oxide perovskite materials to manipulate their optical and electrical properties. Through such studies, this project anticipates being able to reduce the bandgaps of top-performing PE materials while constructing a favourable microstructure to facilitate the generation of ultra-high photovoltages as well as boosting photocurrent by ensuring optimal light absorption. The project’s success could instigate breakthroughs in mechano-solar-electric multi-energy converters and green electricity generation for Internet of Things (IoT), which necessitate long lifespan and miniaturization. It could also fundamentally unify two significant but contradictory components, the PEs and PVs.
In line with the goal of engineering the optical bandgaps of renowned, high-performance oxide perovskite piezoelectric materials, champion piezoelectric materials have been doped and co-doped with various elements that show promise in altering the band structures of these piezoelectric compositions. The work on compositional engineering has been progressing largely as planned. A total of 40 sub-compositions and their corresponding ceramics have been fabricated and comprehensively characterized in terms of their physical, optical, and electrical properties. This is considered a significant volume of work. As a foundational result, a comprehensive understanding of the chemical behaviour and evolution of functional properties of the parent compositions has been achieved. This accomplishment has paved the way for further compositional engineering in this project. Furthermore, the work on certain dopants has led to preliminary conclusions that the local chemical environment is crucial in terms of band structure evolution. Different dopants could serve as effective tools for tuning optical and optoelectrical properties for a variety of applications. Among the dopants that have been tested, a pair of elements as co-dopants has shown early signs of success as they have maintained excellent piezoelectricity and simultaneously demonstrated significantly improved dark conductivity, which could indicate a reduced bandgap. A newly discovered electrical behaviour could also contribute to improving the photovoltaic efficiency, one of the project’s ultimate goals. However, the origin and cause of these phenomena require further research in the next stage of this project. In alignment with the goal of enhancing the photovoltaic efficiency of the piezoelectric materials, device configurations have been created and characterized according to the plan. Promising phenomena, including cumulative opto-ferroelectric response and efficiency increase via domain manipulation, have been discovered, holding promise for achieving the project’s goals.
Some of the unexpected roles of dopants in parent compositions, coupled with the enhanced photovoltaic efficiency following domain manipulation, could significantly advance our understanding of bandgap engineering and the optoelectrical response of ferroelectric materials. Additional work is required to solidify the results obtained. In due course, the combination of current and future findings could lead to a substantial breakthrough in our understanding of band structures in ferroelectrics and the potential of their photovoltaic efficiencies in real-world applications.