An evaporator for vaporizing an organic material to be deposited on a flexible substrate where the evaporator includes an evaporation tube having a wall encompassing a cavity for vaporizing the organic material, at least one heating device arranged adjacent to the wall and being adapted to heat the evaporation tube, and at least one nozzle assembly protruding from the evaporation tube. The nozzle assembly further comprises a nozzle cover with an opening, and a shutter for selectively opening and closing the opening of the nozzle cover. The shutter is adapted to have in operation of the evaporation tube a temperature within a shutter temperature range of 140° C. such that the temperature of the nozzle cover is within the shutter temperature range.