As perovskite solar cells show tremendous potential for widespread applications, we find that adding inorganic thermal-stable cesium ions into MAPbI3 results in significantly improves thermal stability. For un-encapsulated perovskite devices, the energy conversion efficiency maintains about 75% of its original value (over 15%) in the MA0.85Cs0.05PbI3 device under 80 min of heating at 140°C in a dry atmosphere (RH≤30%). With significantly improved thermal stability achieved by a convenient proces
