Organo-metal halide peorvskites are attracting considerable attention because of their potential applications to optoelectronics devices including solar cells and light emitting diodes (LEDs). In 2014, Friend and co-workers have prepared color tunable LEDs based on solution-proicessed organometal halide perovskites by tuning the halides composites [1]. They achieved emission at room temperature, although the emission could only be observed at liquid nitrogen temperature in the past. In my seminar, I will discuss about their strategy to have a high-efficeint LEDs based on perovskites.