Multifunctional Solar Cells: New Research Enhances Bulk Photovoltaic Efficiency by 35% and Expands Potential Applications

A research team led by Associate Professor Yang Bai from the University of Oulu has made a significant breakthrough in the field of multifunctional energy harvesting. Their latest study, published in Advanced Electronic Materials, has been highlighted as the back cover of the journal. The research focuses on improving the efficiency of the bulk photovoltaic effect (BPVE) by manipulating ferroelectric domains in oxide perovskite crystals.

The team, which includes Vasilii Balanov, Jani Peräntie, Jaakko Palosaari, Suhas Yadav, and Yang Bai, has presented their findings in the article titled Study on Influence of AC Poling on Bulk Photovoltaic Effect in Pb(Mg1/3Nb2/3)O3-PbTiO3 Single Crystals. Their work advances the understanding of BPVE, a phenomenon that has the potential to surpass the efficiency limits of traditional semiconductor-based solar cells.

Unlike conventional solar cells that rely on p-n junctions to convert sunlight into electricity, BPVE generates its own “self-junction” and, theoretically, could overcome the Shockley-Queisser efficiency limit that restricts single-junction silicon-based solar cells. However, the practical application of BPVE has been hindered by its low power output compared to conventional photovoltaic technology.

In this study, Bai’s team demonstrates that by creating a stacked domain structure, they can achieve a 35% improvement in the output power of BPVE-based cells. Domains are submicron-sized regions within a material where spontaneous polarizations align in the same direction. These domains can be controlled by applying an external electric field.

The key advancement in their research lies in the application of an AC poling electric field, which helps to better align the microstructure of the ferroelectric domains. Unlike the conventional DC field method, AC poling results in a more stable and better-aligned domain structure that remains intact even after the field is removed. This improved alignment reduces charge recombination, leading to enhanced energy conversion efficiency.

According to Bai, this development paves the way for more efficient BPVE-based energy harvesting systems and multifunctional devices. “The first concrete applications will be in small-scale sensing and computing devices, where light of different wavelengths can serve as an additional input for operation,” he explained. The team has already demonstrated BPVE’s potential in filterless color sensors, and future applications could include neuromorphic computing components and multi-source energy harvesters for IoT devices.

Despite the significant progress, challenges remain. One of the key obstacles is finding materials with both a narrow band gap—needed to absorb more visible light—and a large spontaneous polarization, which enhances open-circuit voltage. Currently, most available materials only possess one of these properties, making it necessary to explore new material options.

The study was supported by the European Research Council through an ERC Starting Grant awarded to Yang Bai for the UNIFY project in 2022. While there is still considerable work ahead, this research marks an important step toward the development of next-generation solar energy solutions and multifunctional electronic devices.