Perovskite-silicon solar cells convert a greater proportion of sunlight into electricity compared with traditional solar cells. This property promises a cheaper and more efficient solar energy device, but perovskite is not ready for commercial use as it is unstable and degrades under illumination. An international research team has demonstrated that substituting the cation in the structure improves the stability as a result of both external pressure and chemical compression shift.

Under illumination, halides in the perovskite cell segregate into iodide-rich and bromide-rich domains and a Schematic shows the suppression of segregation by compressing a mixed-halide perovskite. The orange color (on the right side of the panel) represents the initial mixing ratio, and the light- and dark-colored regions represent bromine and iodine grains, respectively. Source: Eline M. Hutter et al.Schematic shows the suppression of segregation by compressing a mixed-halide perovskite. The orange color (on the right side of the panel) represents the initial mixing ratio, and the light- and dark-colored regions represent bromine and iodine grains, respectively. Source: Eline M. Hutter et al.large part of the light spectrum is converted into heat instead of electricity. Speculating that spontaneous separation of the halides might be prevented by subjecting the material to high pressure, a transient absorption spectrometer was used to measure the electronic properties of perovskites under pressure. Halide separation was observed to cease under 3000 bar of pressure, confirming that unit cell volume is an important factor determining the values at which mixed-halide perovskites are stable.

The findings reported in Cell Reports Physical Science indicate that any iodide:bromide ratio could be thermodynamically stabilized against halide segregation by tuning the crystal volume and compressibility. Scientists from AMOLF (the Netherlands), Yonsei University (South Korea) and Imperial College London contributed to this research.

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