North Carolina State University scientists have discovered that channeling ions into defined pathways in perovskite materials improves the stability and operational performance of perovskite solar cells.

The discovery paves the way for a new generation of lighter, more flexible, and more efficient solar cell technologies suitable for practical use.

The study titled ‘A multiscale ion diffusion framework sheds light on the diffusion–stability–hysteresis nexus in metal halide perovskites’ is published in Nature Materials journal.

In the experiment, the scientists studied the grain boundaries in perovskite materials. They found that while ‘growing’ a perovskite, the material forms a series of crystals or grains.

The generation of charges for electric current and absorption of light is possible in perovskite through these grains.

However, they observed that the positioning of grains is much more likely to be disoriented in the material, and such an area where grains touch each other is termed to be grain boundary. They found that perovskites are ionic materials and the migration of ions results in certain chemical and structural changes in the material itself.

According to Aram Amassian, the corresponding author of the study, strengthening the grain boundaries helps understand what needs to be done to make perovskites more stable and efficient.

The first author of the study, Masoud Ghasemi said, “What we’ve found is that grains are better protected from impairment when the ions move predominantly along the grain boundary. Designing stronger grain boundaries that protect the grains is essential to block migrating ions and other harmful species like oxygen from entering the grains, mitigating problematic chemical and structural changes in the material.”

The researchers discovered that when a voltage is applied to a perovskite, ions migrate through the material and an increase in this activity makes the material unstable and inefficient.

The team claimed that the migration of ions could be one of the potential reasons stopping the achievement of long-term operational stability in perovskite solar cells.

Figure 1: Migration of ions in perovskite material. Source: NC State University

“This is an important insight because there are established techniques we can use to engineer perovskite materials and their grain boundaries. Observing the grain boundaries opens the door to a host of new technologies, such as flexible, lightweight solar cells, or layered solar cells (known as tandems) that can be far more efficient than the solar harvesting technology used today in so-called solar farms,” Amassian said.

The work may also inform the development of more efficient energy storage technologies.

In an experiment performed by experts at Germany’s Helmholtz-Zentrum Berlin, experts claimed to have achieved 32.5% conversion efficiency in tandem solar cells, the highest ever for this technology.

Researchers at the Indian Institute of Technology, Roorkee developed a prototype of a low-cost, high-quality perovskite solar cell that achieved a stable conversion efficiency of 17.05%. The experts said that their perovskite solar cell leads to the optimum phase distribution, enlarged grain size, and comes with enhanced crystallinity.