A rapid layer‐specific annealing on perovskite active layer enabled by ultraviolet (UV) light‐emitting diode (LED) is demonstrated and efficiency close to 19% is achieved in a simple planar inverted structure ITO/PEDOT:PSS/MAPbI3/PC71BM/Al without any device engineering. These results demonstrate that if the UV dosage is well managed, UV light is capable of annealing perovskite into high‐quality film rather than simply damaging it. Different in principle from other photonic treatment techniques that can heat up and damage underlying films, the UV‐LED‐annealing method enables layer‐specific annealing because LED light source is able to provide a specific UV wavelength for maximum light absorption of target film. Moreover, the layer‐specific photonic treatment allows accurate estimation of the crystallization energy required to form perovskite film at device quality level.

In article number 1902898, Dawen Li and co‐workers demonstrate a rapid layer‐specific annealing on perovskite active layer enabled by UV‐LEDs. An efficiency close to 19% is achieved for a simple inverted planar structure without any interfacial engineering. Perovskite solar cells with photonic annealing of 12 seconds using UV‐LEDs show better performance than those with traditional hot‐plate heating for 1 hour.