Researchers at EPFL have found a way to dramatically reduce energy loss and boost efficiency in perovskite solar cells by incorporating rubidium using lattice strain—a slight deformation in the atomic structure that helps keep rubidium in place.

Solar energy is one of the most promising solutions for reducing our dependence on fossil fuels. But making solar panels more efficient is a constant challenge. Perovskite solar cells (PSCs) have been a game-changer, offering rapid improvements in efficiency and potential for low-cost manufacturing. However, they still suffer from energy losses and operational stability issues.

The challenge with wide-bandgap perovskites

Perovskite solar cells, particularly those used in tandem configurations, rely on wide-bandgap (WBG) materials—semiconductors that absorb higher-energy (“bluer”) light while letting lower-energy (redder) light pass through—to maximize efficiency. However, wide-bandgap perovskite formulations often suffer from phase segregation, where different components separate over time, which causes a decline in performance.

One solution is to add rubidium (Rb) to stabilize WBG materials, but there’s a catch: Rb tends to form unwanted secondary phases, which reduces its effectiveness in stabilizing the perovskite structure.

The EPFL solution: Strain to the rescue

Scientists led by Lukas Pfeifer and Likai Zheng in the group of Michael Grätzel at EPFL have now found a way to force Rb to stay where it’s needed. By utilizing “lattice strain” of the perovskite film, they managed to incorporate Rb ions into the structure, which prevented the unwanted phase segregation. This novel approach not only stabilizes the WBG material but also improves its energy efficiency by minimizing non-radiative recombination—a key culprit in energy loss.

The work is published in the journal Science.

The researchers used lattice strain—a controlled distortion in the atomic structure—to keep Rb locked into the perovskite lattice. They did this by fine-tuning the chemical composition and precisely adjusting the heating and cooling process. Rapid heating followed by controlled cooling induced strain, preventing Rb from forming unwanted secondary phases and ensuring it stayed integrated within the structure.

Verifying and fine-tuning the approach

To confirm and understand this effect, the team used X-ray diffraction to analyze structural changes, solid-state nuclear magnetic resonance to track the atomic placement of Rb, and computational modeling to simulate how the atoms interact under different conditions. These techniques provided a detailed picture of how strain stabilized Rb incorporation.

Besides lattice strain, they also found that introducing chloride ions is key to stabilizing the lattice by compensating for the size differences between the incorporated elements. This ensured a more uniform distribution of ions, reducing defects and improving overall material stability.

The result? A more uniform material with fewer defects and a more stable electronic structure. The new perovskite composition, enhanced with strain-stabilized Rb, achieved an open-circuit voltage of 1.30 V—an impressive 93.5% of its theoretical limit. This represents one of the lowest energy losses ever recorded in WBG perovskites. Moreover, the modified material showed improved photoluminescence quantum yield (PLQY), indicating that sunlight was being more efficiently converted into electricity.

Impact on renewable energy

Reducing energy loss in perovskite solar cells could lead to more efficient and cost-effective solar panels. This is especially important for tandem solar cells, where perovskites are paired with silicon to maximize efficiency.

The findings also have implications beyond solar panels—perovskites are being explored for LEDs, sensors, and other optoelectronic applications. By stabilizing WBG perovskites, the EPFL research could help accelerate the commercialization of these technologies.