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

Abstract

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 ≈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‐ethylenedioxythiophene):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.