Non-conjugated water/alcohol soluble polymers with different oxidation states of sulfide as cathode interlayers for high-performance polymer solar cells

A series of non-conjugated water/alcohol soluble copolymers containing diphenyl sulfide, diphenyl sulfoxide or diphenyl sulfone in the main chain were synthesized. The surfactant-like functionalities in side chains endow the polymers with outstanding solubility in highly polar solvents and excellent electron extraction abilities, while the limited conjugation length of main chains renders the polymers weak optical absorption. These unique characteristics make the polymers excellent cathode interfacial layers, which contribute to highly efficient polymer solar cells (PSCs) with power conversion efficiencies of 8-9%. More importantly, some of them can yield highly efficient PSCs in a relative large interlayer thickness range of 2-20 nm. The results suggest that these polymers are promising candidates for use as cathode interfacial layers in single-junction PSCs and as recombination layers in multi-junction PSCs.