Harnessing light with ferroelectric crystals: a new path in energy harvesting
Their study demonstrates that applying an alternating current (AC) poling electric field to oxide perovskite crystals can improve the electric output of BPVE-based devices by 35%. This advancement brings BPVE-based energy harvesting closer to practical applications, offering a new approach to overcoming efficiency limitations in conventional solar cells.
The team, which includes Vasilii Balanov, Jani Peräntie, Jaakko Palosaari, and Suhas Yadav, explored how manipulating ferroelectric domains within the crystals can enhance energy conversion efficiency. Unlike traditional photovoltaic cells that rely on semiconductor p-n junctions, BPVE can generate electricity without these junctions, potentially surpassing the Shockley-Queisser efficiency limit. By optimizing the alignment of microscopic domains within the material, the researchers have taken a crucial step toward developing more efficient energy-harvesting technologies for photonic, computing, sensing, and IoT applications.
In ordinary solar cells, the process of harvesting solar energy and converting it into electricity is based on the formation of p-n junctions in semiconductors. While p-n junctions were invented more than a century ago and are now widely used in the silicon industry, the bulk photovoltaic effect (BPVE) is a more recently discovered physical phenomenon, first identified in the 1960s–1970s. Unlike conventional solar cells, BPVE does not rely on p-n junctions to generate electricity from solar energy. Instead, it forms its own 'self-junction' and, in theory, could surpass the Shockley-Queisser limit, which restricts the efficiency of single p-n junction-based solar cells, clarifies associate professor Yang Bai from Microelectronics research unit.
Practical application of BPVE is challenging though. The output power of BPVE-based cells is still negligible compared to those of p-n junction-based photovoltaic cells. In the study, Prof. Bai’s team proves that a stacked domain structure can achieve 35 % improvement on the output power of BPVE-based cells. A domain is a submicron-sized region containing spontaneous polarizations orienting in the same direction, which can be switched by applying an external electric field.
The improved electric output of Prof. Bai’s BPVE device is achieved by applying an alternating current (AC) poling electric field. This process helps align the microscopic structures (domains) inside the crystals more effectively than the traditionally used direct current (DC) field. After removing the electric field, the domains stay at that better aligned state. Consequently, the better aligned domains help to reduce recombination of electric charge carriers, and thus the energy conversion efficiency increases. The results of the work pave a way towards developing more efficient BPVE cells that can help to unlock multifunctionality in future devices used in photonics, computing, sensing and energy harvesting.
‘The first concrete applications will be in small-scale sensing and computing devices, where in addition to the electric signals, we can input light of different wavelengths as an extra degree of freedom for operation. For example, we have previously proven the use of BPVE in filterless colour sensor. Other examples include components for neuromorphic computing and multi-source energy harvesters for IoT (internet of things) devices’, says Yang Bai.
Despite this scientific advance, there is still plenty of research to be done. Prof. Bai is aware of the challenges and the future goals are clear. Prof. Bai's team will continue working to find materials that have both good light absorption and strong spontaneous polarization for higher output voltage, as most current materials only have one of these properties.
Biography
Dr. Yang Bai is Associate Professor in energy harvesting materials and self-sufficient sensor systems at the Microelectronics Research Unit, University of Oulu, Finland. He specializes in research and teaching of energy harvesting and sensing technologies, including materials and devices. He obtained Ph.D. in 2015 from University of Birmingham, UK. He was awarded the Marie Sklodowska-Curie Individual Fellowship in 2016 and the ERC Starting Grant in 2021. He also chairs the Energy Materials and Systems Division of the American Ceramic Society in 2024-2025.
