A laminated organic light-emitting device (OLED), manufacturing method thereof and a display device comprising the laminated organic light-emitting device, reducing a layer number of the laminated organic light-emitting device and improving luminous efficiency. The laminated organic light-emitting device comprises a connection layer for connecting two adjacent light-emitting units (2001, 4001), the connection layer comprising a lower sub-connection layer (3012) and an upper sub connection layer (3011) sequentially connected, and at least one sub connection layer is a gradient-doped connection layer.
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