A hyperbranched conjugated polymer as the cathode interlayer for high-performance polymer solar cells

An alcohol-soluble hyperbranched conjugated polymer HBPFN with a dimethylamino moiety is synthesized and used as a cathode interlayer. A PCE of 7.7% is obtained for PBDTTT-C-T/PC71 BM based solar cells. No obvious interfacial dipole is found at the interface between the active layer and HBPFN however, an interfacial dipole with the cathode could be one of the reasons for the enhanced performance.