Conjugated polyelectrolytes based on n-type backbone (n-CPEs) were recently developed as highly efficient cathode interlayers for polymer solar cells (PSCs), but the relevance between structure and property of n-CPEs has not been fully understood yet. Herein, three new self-doping n-CPEs based on the diketopyrrolopyrrole (DPP) alternated fluorene framework were reported. The effect of the number and location of polar groups on the properties of the new n-CPEs has been systematically studied. It can be found that the photoelectric properties of n-CPEs were sensitive to the number and location of polar groups. A tunable work function (WF), interfacial interaction, and conductivity of these n-CPEs can be readily realized by regulating the number and location of polar groups on the electron skeleton. The polar groups directly appending on the electron-withdrawing DPP unit can promote a stronger n-type self-doping and lower WF than the ones attached on the electron-pushing fluorene unit. Increasing the number ...