EPFL researchers improve the performance of perovskite solar cells via rubidium – SPE

January 6, 2026
Valerie Thompson

Researchers at the Ecole Polytechnique Federale de Lausanne (EPFL) in Switzerland recently led efforts to improve the optoelectronic performance of perovskite using small radius rubidium ions (Rb⁺) chemistry. In two recent studies, targeting two different structural locations and operating through different physical mechanisms, the researchers described methods using Rb⁺ in perovskite films to increase the stability of perovskite solar cells in the laboratory.

In the most recent study “In-situ boundary bridging unlocks multi-grain domain carrier diffusion in polycrystalline metal halide perovskites”, published in Nature communication, the researchers unraveled the ‘remarkable’ effects of Rb⁺ cations when selectively introduced at the grain domain boundaries (GDBs) of polycrystalline perovskite films.

“By using a crown ether complex to precisely deliver Rb⁺ in the perovskite film we observed remarkable improvements in carrier diffusion length and carrier lifetime,” said corresponding author Michael Grätzel. pv magazine.

“Together with our employees in Dalian, we have further demonstrated that Rb⁺ facilitates cross-border charge transport through the formation of a one-dimensional RbPbI₃ phase,” he added.

“These cross-localized cations effectively bridge adjacent grains and promote transport across multiple grain domains,” corresponding author Likai Zheng shared. pv magazine.

Noting that Rb⁺ Because cations cannot reside at the A cation site in normal bandgap perovskites due to their small size, the researchers proposed a ‘universal post-treatment strategy’ based on a supramolecular crown ether-assisted slow release with ‘precise delivery of Rb⁺ cations to GDBs where they form in situ one-dimensional (1D) Rb-based non-perovskite phase bridge that facilitates the passivation of defects and enables carrier diffusion.’

Perovskite solar cells made with the modified film had a certified champion efficiency of 25.77%, with the result validated by China’s Fujian Metrology Institute (FMI) and the National Photovoltaic Industry Measurement and Testing Center (NPVM).

In addition, “remarkable” stability was noted with 99.2% of initial efficiency maintained after 1,300 hours of continuous light from one sun under maximum powerpoint tracking, based on the International Summit on Organic Solar Cells Stability protocol ISOS-L-1I.

Researchers from China’s Dalian University of Technology collaborated, as did teams from the Chinese Academy of Sciences, Lanzhou University and Hong Kong University of Science and Technology (Guangzhou).

In an earlier study “Strain-induced incorporation of rubidium into wide bandgap perovskites reduces photovoltage loss”, published in April in Sciencethe team developed a lattice voltage approach to incorporate Rb⁺ in 1.67 eV wide-bandgap (WBG) perovskite films aimed at greater stability of solar cells.

“In our research we discovered that Rb⁺ can occupy the A site in the perovskite lattice, and that its incorporation depends on the triple halide composition, and is enabled by the lattice tension,” Zheng said.

The researchers noted that the method, which used chloride to facilitate the absorption of Rb⁺ in the perovskite lattice, allowed a “marked suppression of halide phase segregation, which is a known source of instability in mixed-halide WBG perovskites.”

The team demonstrated the film’s properties in a triple halide perovskite solar cell (PSC) with a power conversion efficiency (PCE) of 20.65% and an open-circuit voltage of 1.30 V (Voc). These results correspond to 93.5% of the radiative Voc limit, “which represents the lowest photovoltage loss compared to the theoretical limit observed in WBG perovskites,” according to the study.

The results were attributed to a “substantial improvement in the stability of the lattice structure” to keep Rb confined in the perovskite lattice.

The perovskite solar cells were based on perovskite material containing cesium (Cs), methylammonium (MA), formamidinium (FA) in a stack as follows: indium tin oxide (ITO) on glass substrate, tin oxide (SnO₂) electron transport layer, perovskite absorber, spiro-OMeTAD hole transport layer, gold contacts, with spiro-OMeTAD abbreviation for 2,2′,7,7′-tetrakis (N,N-di-p-methoxyphenylamino)-9,9′-spirobifluorene.

The research was co-led by a team from Nanjing University of Aeronautics and Astronautics (NUAA) with the participation of teams from the National University of Singaporethe University of Ioannina and Politecnico di Milano.

Looking ahead, the researchers say they remain focused on “fully understanding and leveraging the multifaceted benefits of Rb⁺ in perovskite solar cells.”