Development of Self-Doped Conjugated Polyelectrolytes with Controlled Work Functions and Application to Hole Transport Layer Materials for High-Performance Organic Solar Cells

A series of anionic self-doped conjugated polyelectrolytes (CPEs) by copolymerization of a 1,4-bis(4-sulfonatobutoxy)benzene moiety with different counter monomers of thiophene, bithiophene, and terthiophene is reported. The CPEs show high conductivity of approximate to 10(-4) S cm(-1) due to being self-doped in a neutral state and exhibit excellent hole transporting property in the out-of-plane direction, compared with poly(3,4-ethylened ioxythiophene):poly(styrene-sulfonate) (PEDOT:PSS). Moreover, the CPE incorporating a less electron-donating unit from terthiophene to thiophene exhibits a higher work function and therefore, PhNa-1T incorporating thiophene shows a relatively high work function of 5.21 eV than 4.97 eV of PEDOT: PSS. This can induce a higher internal field in the solar cell device, facilitating efficient charge collection to the electrode. As a result, polymer solar cell devices incorporating the CPEs as a hole transporting layer achieve enhanced photovoltaic performances from those of the conventional PEDOT: PSS-based devices. The solar cell efficiency reaches up to 9.89%, which is among the highest values demonstrated by PCE-10-based normal-type organic solar cells.