Tandem organic light-emitting diodes (OLEDs) with an organic-organic intermediate connector, consisting of an n-type doped electron-transporting layer (e.g. Li-doped Alq as shown in the figure) and nondoped hexaazatriphenylene hexacarbonitrile (HAT-CN), exhibit reduced drive voltage, improved voltage stability, and improved power efficiency. Moreover, this intermediate connector can be formed by thermal evaporation at temperatures lower than 300 degrees C, which simplifies the fabrication process of the OLEDs.