Based on the reported ion migration under an electric field in hybrid lead halide perovskites we have developed a bright, light-emitting electrochemical cell with CH3NH3PbBr3 single crystals directly grown on vertically aligned carbon nanotube forests as contact electrodes. Under the applied electric field, charged ions in the crystal drift and accumulate in the vicinity of the electrodes, resulting in an in operando formed p-i-n heterojunction. The decreased interface energy barrier and the strong charge injection due to the CNT tip enhanced electric field result in a bright green light emission up to 1800 cd/m(2) at room temperature (average approximate to 60 cd/m(2)). Beyond the light emission, this original device architecture points to the possibility of implementing vertically aligned CNTs as electrodes in operationally stable perovskite-based optoelectronic devices.