Reviewed by Lexie CornerMar 14 2025
In a recent study published in The Journal of Advanced Electronic Materials, researchers from the University of Oulu, led by Associate Professor Yang Bai, made progress in the field of multifunctional energy harvesting. Their research provides new insights into the photovoltaic effect in ferroelectric crystals.
Image Credit: Nguyen Quang Ngoc Tonkin/Shutterstock.com
The study focuses on how manipulating ferroelectric domains in oxide perovskite crystals can enhance the electric output of the bulk photovoltaic effect.
In ordinary solar cells, the mechanism of harvesting the solar energy and then converting them into green electricity is based on the formation of p-n junctions of semiconductors. While the p-n junction has been invented for more than a century and is widely used in the silicon industry nowadays, the BPVE is a more recently discovered physical phenomenon from the 1960s-1970s.
Yang Bai, Associate Professor, Microelectronics Research Unit, University of Oulu
Bai explained, “The BPVE does not rely on p-n junctions to work under solar energy. It forms its own ‘self-junction’ and, theoretically, it may break the physical limit of the Shockley-Queisser limit that prevents single p-n junction-based solar cells from being more efficient.”
While the output power of BPVE-based cells is still limited compared to p-n junction-based photovoltaic cells, the application of BPVE in practice remains challenging. In this study, Bai's team demonstrates that a 35% increase in the output power of BPVE-based cells can be achieved by constructing a stacked domain structure.
An external electric field is used to switch the spontaneous polarizations within a domain, which is a submicron-sized area. Applying an AC poling electric field enhances the electric output from Bai's BPVE device, as the microstructure (domains) inside the crystals become more aligned than with the typically used DC field.
The domains remain aligned even after the electric field is removed, leading to increased energy conversion efficiency. This alignment reduces electric charge carrier recombination.
The findings have potential implications for future photonic, computing, sensing, and energy harvesting devices, as they could lead to more multifunctional and efficient BPVE cells.
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 a filterless color sensor. Other examples include components for neuromorphic computing and multi-source energy harvesters for IoT (Internet of Things) devices.
Yang Bai, Associate Professor, Microelectronics Research Unit, University of Oulu
Despite the current breakthrough, much more research is needed. Yang is aware of the challenges and has a clear vision for the future.
While we are advancing in the working mechanism inside the materials, the challenge still lies in the band gap of the materials, where we ideally need a material that simultaneously has a narrow band gap (to maximize visible light absorption) and a large spontaneous polarization (to maximize the open-circuit voltage).
Yang Bai, Associate Professor, Microelectronics Research Unit, University of Oulu
“We have limited options for such materials. Most available materials nowadays only possess either a narrow band gap or a large spontaneous polarization, not both. In the near future, we will attempt to expand the material options”, said Yang Bai.
The European Research Council funded this study. Yang Bai, an Assistant Professor, received an ERC Starting Grant in 2022 for the UNIFY project.
Journal Reference:
Balanov, V., et al. (2025) Study on Influence of AC Poling on Bulk Photovoltaic Effect in Pb(Mg1/3Nb2/3)O3‐PbTiO3 Single Crystals (Adv. Electron. Mater. 3/2025). Advanced Electronic Materials. doi.org/10.1002/aelm.202570009.