Solution-Processable PEDOT for Organic Solar Cells: From One-Pot Synthesis to Kinetically-Controlled Polymerization

The updating of poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) hole transporting material (HTM) is crucial for organic solar cells (OSCs). Despite decades of development in PEDOT:PSS and its derivatives, a comprehensive understanding of their supramolecular polymerization mechanisms remains elusive, precluding the attainment of the optimal architectures and functions. Herein, it is shown that the synthesis of PEDOT:PSS follows the principle of oxidative polymerization-induced electrostatic self-assembly, with the kinetic behavior strongly correlated to the volume of PSS polyanion matrix. Moreover, a kinetically controlled polymerization approach is proposed to synthesize PEDOT HTMs with exceptional time efficiency by prematurely halting the rapid polymerization process within a low-volume PSS matrix. The reduced interference from PSS confers unique advantages to the methodology in achieving highly oxidized and interconnected PEDOTs. This leads to comprehensive improvements in the physico-chemical properties of PEDOT:PSS, significantly enhancing OSC efficiency to 20.04%. Furthermore, the optimized PEDOT maintains exceptional semiconducting characteristics and outstanding OSC efficiency even at an unprecedentedly high PSS insulator content of 94.12%. The substantial increase in loading significantly amplifies the manifestation of polyanion functionalities, such as improving colloidal stability, thereby facilitating the resurgence of previously underutilized naphthalene sulfonate polyanion in the fabrication of high-quality, solution-processable PEDOT HTMs.