Researchers found a technique to reduce energy loss and boost efficiency of perovskite solar cells by incorporating rubidium using lattice strain. [Image: Daniel Bosma/ Getty Images]
Perovskite solar cells represent the fastest-developing photovoltaic technology to date, with a power-conversion efficiency (PCE) that has skyrocketed from 3.8% to 26.7% in the last 15 years. To further boost PCE, tandem architectures have been created that combine a wide-bandgap perovskite top cell with a narrow-bandgap bottom cell. However, light-induced phase segregation—a common occurrence in wide-bandgap perovskite formulations—limits their efficiency and stability.
Now, a team of researchers in Switzerland, Singapore and China have discovered a promising strategy to prevent phase segregation in wide-bandgap perovskite solar cells (Science, doi: 10.1126/science.adt3417). They found that using strain to incorporate rubidium ions into the lattice of perovskites induces halide homogenization, which both stabilizes the material and improves efficiency.
Stabilized by strain
The PCE of wide-bandgap perovskite solar cells remains considerably lower than their theoretical limit, possibly due to an inhomogeneous halide distribution. Introducing rubidium additives has the ability to homogenize film composition, but rubidium tends to form unwanted secondary, non-perovskite phases with lead iodide.
Led by the group of Michael Grätzel, Ecole Polytechnique Fédérale de Lausanne, Switzerland, the research team found that small amounts of rubidium ions can be incorporated into the lattice of triple-halide perovskite films and stabilized by strain. X-ray diffraction techniques, solid-state nuclear magnetic resonance and computational studies indicate a reduction in phase segregation and non-radiative recombination resulting from strain-induced rubidium incorporation.
In addition, a prepared wide-bandgap device achieved an open-circuit voltage of 1.3 V on the basis of a perovskite with a bandgap of 1.67 eV, a value representing the lowest open-circuit voltage deficit reported and 93.5% of the radiative theoretical limit. It also showed improved photoluminescence quantum yields that exceeded 14%.
The research team found that small amounts of rubidium ions can be incorporated into the lattice of triple-halide perovskite films and stabilized by strain.
Enhancing performance
To leverage lattice strain, the researchers fine-tuned the chemical composition of the material, then precisely adjusted the heating and cooling process to keep the rubidium locked into the perovskite lattice. Quick heating and controlled cooling created strain, ensuring that the rubidium didn’t form unwanted secondary phases and remained integrated in the structure.
The findings have the potential to enhance the performance of perovskite solar cells, as well as light-emitting diodes, sensors and other optoelectronic applications of wide-bandgap perovskites.