Researchers develop new method to boost perovskite solar cell efficiency to 26%

Researchers have developed a new method to improve the efficiency and durability of perovskite solar cells by controlling the material's crystallization process. The study shows that a temporary liquid phase can help produce larger, more uniform crystals and reduce defects. The team, co-led by researchers at the University of California, San Diego (UC San Diego), used this method to improve perovskite-based solar cells and light-emitting diodes. These devices achieved efficiencies of approximately 24% to 26%, among the highest reported values for perovskite devices.

Solar cells made with this technology retained most of their initial efficiency after eight weeks of continuous operation under simulated sunlight. The liquid phase aids crystal growth, and perovskite materials help make solar technology more economical while offering high efficiency. These materials can be processed from liquid solutions and deposited as thin films, potentially reducing the energy and complexity required for manufacturing compared to traditional silicon solar cells. However, producing high-quality perovskite films remains challenging. These films typically contain many small crystals, and the boundaries between crystals are called grain boundaries. Defects in these regions can cause energy losses, reducing device performance. This problem becomes more pronounced when manufacturers attempt to produce larger-area solar panels, as maintaining efficiency over larger areas becomes difficult.

Solving the crystal growth problem

To address this issue, a research team led by David Fenning, a professor of chemistry and nanoengineering at UC San Diego, collaborated with colleagues at Princeton University and Sungkyunkwan University in South Korea. They added zinc bromide and methylammonium chloride to the solution used to produce a material known as halide perovskite. When heated, these additives formed a low-melting-point mixture known as a eutectic. This mixture formed a temporary liquid around the boundaries of growing crystals, allowing the crystals to rearrange and form a more ordered structure.

As heating continued, the methylammonium chloride evaporated, leaving zinc concentrated around the crystal boundaries. The remaining zinc helped neutralize electronic defects that could disrupt charge transport. "We introduced a new way to regulate halide perovskite growth by developing an additive mixture that actively evolves during the crystallization process," said Connor Dolan, co-first author of the study and a chemistry and nanoengineering Ph.D. graduate from the Fenning lab. "What's even cooler is that the final product eliminates the performance-limiting defects at the crystalline grain edges."

The researchers used advanced X-ray imaging techniques to observe changes in the material at extremely small scales. Their measurements showed that during heating, the regions around crystal boundaries became disordered and liquid-like, then returned to an ordered state after the additional salts evaporated and crystal growth ended. The treatment produced larger crystals with fewer structural defects and a more uniform distribution of chemical properties. The researchers were also interested in why this solid-liquid-solid transition occurs at the same temperature.

Potential for improved device performance

The improved crystal structure translates to better device performance. In solar cells, sunlight excites electrons, leaving behind positively charged holes. The length of time these electron-hole pairs survive helps indicate how effectively the material supports solar energy conversion. "Perovskites made with the eutectic-formed additives have the longest-lived electron-hole pairs of any direct-bandgap semiconductor to date, demonstrating the potential of this approach," Dolan noted. The researchers also tested the method across different perovskite compositions, finding it effective in every chemical system they examined.

"It seems like every single one we tried worked!" Dolan added. "I hope this mechanism has a chance to be truly universal and provide a platform for further innovation in the perovskite community."

The team is currently investigating other eutectic mixtures to better control the crystallization process. The researchers hope this approach will provide a broader strategy for producing high-quality perovskite materials and support the development of high-efficiency solar technologies that can be manufactured at larger scales. The study was published in the journal Science.

Item	Specification
Efficiency	24% - 26%
Test duration	Eight weeks

Breakthrough in perovskite solar cell technology

Perovskite solar cells have attracted widespread attention due to their potential for high efficiency and cost-effectiveness. This research demonstrates that by controlling the crystallization process, battery performance can be significantly improved and defects reduced, which is crucial for driving the commercialization of perovskite technology. As demand for solar technology grows, this new method could become key to future high-efficiency solar cell production. The research team's ongoing efforts also show that there is still more room for innovation in the future development of perovskite materials.