Phosphonium conjugated polyelectrolytes as interface materials for efficient polymer solar cells

Abstract

A series of cationic phosphonium-based conjugated polyelectrolytes (CPCPs, named as PFP-F, PFP-Cl, PFP-Br, PFP-I) with different counteranion were developed as individual cathode interface material and ZnO dopant for polymer solar cells (PSCs). The CPCPs are soluble in environmentally friendly polar solvents, which is beneficial to fabricating multilayer organic optoelectronic devices. Besides, the CPCPs show better thermal stability than traditional quaternary ammonium salt-based conjugated polyelectrolytes. The CPCPs perform efficiently as electrode modifiers to lower the work function of metal electrode and possess capability to n-dope PC71BM, both of which contribute to the improved performance of polymer solar cells. Significant enhancement in power conversion efficiency from 6.3% to >9.0% were achieved by employing a thin layer of CPCP between active layer and Al electrode in polymer solar cells with conventional device structure. Moreover, the CPCPs can be used as dopants to ZnO. The formed ZnO:CPCP hybrids can improve the interface contact between bottom contacts and active layer in inverted solar cells, resulting in improved performance.