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 cm² 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.

Science 29 Sep 2016:
DOI: 10.1126/science.aah5557

http://science.sciencemag.org/content/early/2016/09/28/science.aah5557.full