93.5% efficiency: New lattice-strained perovskite solar cells achieve record stability

Scientists in Switzerland have discovered a new method to enhance perovskite solar cell performance by securing rubidium (Rb) within the material, thus significantly lowering energy loss and increasing efficiency.

Led by Lukas Pfeifer, PhD, and Likai Zheng, PhD, from the Swiss Federal Technology Institute of Lausanne (EPFL), the team managed to keep rubidium ions locked into the crystal framework of the perovskite — a group of materials known for their high efficiency and low manufacturing costs in solar cell applications — by applying lattice strain.

By utilizing the controlled distortion in the atomic structure, the pioneering approach not only stabilized wide-bandgap (WBG) material but also improved efficiency by cutting non-radiative recombination, a major cause of energy loss.

A closer look at the study

With Earth receiving around 200,000 times more solar energy each day than the world’s total electricity use, it emerges as a key solution to reduce reliance on fossil fuels. While improving solar panel efficiency remains a challenge, perovskite solar cells (PSCs) have transformed the field, showing quick improvements in efficiency and affordable production potential.

However, PSCs’ development remains hindered by energy loss and stability issues, mainly due to challenges in optimizing them with wide-bandgap (WBG) materials — key semiconductors that absorb high-energy light and boost overall efficiency.

Known for absorbing high-energy light while letting lower-energy light pass, wide-bandgap materials offer major gains in energy capture but are prone to phase segregation, a phenomenon that takes place when different components of the material separate over time, leading to a decline in performance.

While adding rubidium to help stabilize the semiconductors has been proposed as a potential way to address the issue, the element often forms unwanted secondary phases, which limits its ability to strengthen the pervoskite structure.

However, the scientists fine-tuned the material’s composition in a process that involved rapid heating followed by controlled cooling. This created lattice strain, that prevented rubidium from forming unwanted secondary phases and kept it integrated within the crystal structure.

Further evaluations

To validate their approach, the researchers used X-ray scans to monitor structural changes, solid-state nuclear magnetic resonance (NMR) to trace rubidium’s integration, and computer simulations to explore atomic behavior under varying conditions. Together, these techniques proved that lattice strain helps stabilize rubidium within the material.

They also found that adding chloride ions is crucial to stabilizing the lattice by balancing the size differences between the elements, which led to a more uniform ion distribution, reducing defects and improving overall material stability.

As per the results, the new lattice-strained perovskite material achieved an open-circuit voltage of 1.30 volts, an impressive 93.5 percent of its theoretical maximum and one of the lowest energy losses ever recorded in wide-bandgap perovskites.

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Additionally, there was a strong boost in photoluminescence quantum yield (PLQY), showing that the improved structure converts sunlight into electricity more efficiently, with very little energy wasted.

The researchers believe cutting energy loss in perovskite solar cells could pave the way for more efficient and cost-effective solar panels. This is particularly promising for tandem solar cells, which pair perovskites with silicon to maximize energy output.

They suggest the impact of these findings goes well beyond solar panels and that technologies like LEDs, sensors, and other optoelectronic devices could benefit, too. The researchers hope their work will help speed up the commercial use of these technologies, bringing us closer to a future powered by cleaner and more sustainable energy.

The study has been published in the journal Science.