Perovskite solar cells are promising in terms of cost-effective solar energy. Thermal stability has always posed a problem, because it significantly limits the long-term efficiency of a solar cell. Scientists have successfully developed a Perovskite solar call containing Cesium which has attained an efficiency of 21.1%, as well as a world record for reproducibility. In adding Cesium, the scientists at EPFL, let by Michael Saliba, have developed the first Perovskite compound with triple cations (Cs/MA/FA). These new films are more stable in hot conditions and less affected by fluctuations in environmental variables. They have confirmed efficiencies of 21.1%, and exit efficiency of 18% in operational conditions, even beyond 250 h. These properties are essential for commercial production where reproducibility and stability are prime requirements for a large scale cost-effective production of Perovskite solar cells. This study was the result of a collaboration between the laboratories o...