Two easily accessible fluorene-based conjugated oligo-electrolytes (COEs) FTF- and FBF-NBr have been developed as the cathode interfacial layer (CIL) in inverted type polymer solar cells (iPSCs). CILsare interpretative to improving the power conversion efficiency (PCE) and long-term stability of the polymer photovoltaic cell that utilizes a high work function cathode. Compared to the reference devices without interlayer, FBF- and FTF-NBr exhibit significant improvements of the device parameters by reducing the work function of indium thin oxide (ITO). Conjugatedoligo-electrolytes in this work havelow lying HOMO levels -5.54eV for FTF-NBr and -5.77eV for FBF-NBr which are beneficial to hole-blocking ability. The iPSCs with FBF- and FTF-NBr as the inter layer at the cathode side were fabricated to investigate the effect of CIL on the photovoltaic properties. As a result, the PCE of 7.89% with FBF-NBr and 8.05% with FTF-NBr as the CIL has been achieved. Thus, the results indicate that fluorene-based COEs are potential CIL materials for the iPSCs.