  Based on the reported ion migration under 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 (VACNT) 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/m2 at room temperature (average = 60 cd/m2).
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.
