Revealing the effect of oligo(ethylene glycol) side chains on n‐doping process in FBDPPV‐based polymers

Abstract

AbstractThe low doping efficiency of n‐doped systems limits the development of n‐type organic conducting materials. Oligo(ethylene glycol) (OEG) as the flexible chain in conjugated small molecules and polymers may improve doping efficiency. However, OEG side chains also bring unexpected low mobility and poor film morphology. Herein, we propose the stronger solution‐state aggregation plays a dominated role in charge transport and morphology of OEG‐substituted polymer. The solution‐state aggregation also affects doping process. Therefore, we develop a series of polymers based on 3,7‐bis((E)‐7‐fluoro‐1‐(2‐octyldodecyl)‐2‐oxoindolin‐3‐ylidene)‐3,7‐dihydrobenzo[1,2‐b:4,5‐b']difuran‐2,6‐dione (FBDPPV) with different ratios of OEG side chain to investigate the effect of side chain on solution‐state aggregation and n‐doping process. After n‐doped by hexahydro‐1H,3a1H,4H,7H‐3a,6a,9a‐triazaphenalene (TAM), FBDPPV with 50% OEG affords the highest doping efficiency and conductivity, while FBDPPV with 100% OEG shows lower conductivity. Combination of ultraviolet–visible–near infrared absorption spectra, grazing‐incidence wide‐angle X‐ray scattering and atomic force microscopy, we reveal that serious aggregated extent in solution of OEG‐substituted polymer result in phase separation and rough morphology, which are the origins of poor conductivity. Our work provides a new perspective on the effect of the OEG side chain on the doped polymer systems, suggesting suitable solution‐state aggregation is crucial to high doping efficiency and high conductivity.