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Incorporation of rubidium cations into perovskite solar cells improves photovoltaic performance.


All of the cations currently used in perovskite solar cells (PSCs) abide by the tolerance factor for incorporation into the lattice. We show that the small and oxidation-stable Rb(+) can be embedded into a "cation cascade" to create perovskite materials with excellent material properties. We achieved stabilized efficiencies of up to 21.6% (average value: 20.2%) on small areas (and a stabilized 19.0% on a 0.5 cm(2) cell) as well as an electroluminescence of 3.8%. The open-circuit voltage of 1.24 volts at a band gap of 1.63 electron volts leads to loss-in-potential of 0.39 V, versus 0.4 V for commercial silicon cells. Polymer-coated cells maintained 95% of their initial performance at 85°C for 500 hours under full solar illumination and maximum power point tracking.