An organic material for a light emitting device is deposited over a substrate by evaporating the organic material from an evaporation source. The evaporation source comprises a plurality of discrete evaporation cells separated from each other, wherein each of the plurality of discrete evaporation cells contains the organic material. The evaporation source has a length along a first direction and a width along a second direction orthogonal to the first direction, the length being greater than the width. The plurality of discrete evaporation cells is arranged along the first direction. When the organic material is evaporated, a relative location of the evaporation source with respect to the substrate is changed along the second direction, and the evaporation of the organic material is initiated by heating the plurality of discrete evaporation cells.