Electrochromic and photovoltaic properties of benzothiadiazole-based donor-acceptor conjugated polymers with oligo(ethylene glycol) side chains

Introduced oligo(ethylene glycol) (OEG) chains into high-performance donor-acceptor (D-A) type conjugated polymers is a promising strategy to control the π-π stacking, energy levels, solubility, and electrical properties. In this work, a series of novel PDTBF polymers (PDTBF-DTh, PDTBF-ThSe, and PDTBF-Th) were synthesized based on the typical benzothiadiazole-thiophene (BT-Th)-based polymer substituted with OEG side chains to investigate their electrochromic (EC) and photovoltaic performance. The resultant PDTBF polymers had fast switching speed (i.e., chlorobenzene-prepared PDTBF-Th EC film: Tc0.9 = 1.8 s, Tb0.9 = 1.0 s), and high coloration efficiencies (i.e., chlorobenzene-prepared PDTBF-ThSe EC film: 255.50 cm2 C−1). Moreover, the PDTBF-DTh:Y6-based device shows a power conversion efficiency (PCE) of 3.11%. Due to the induced amphiphilic OEG side chains on the backbone of the conjugated polymer, these materials also exhibited green solvent processing potential. It is worth noting that these PDTBF polymers exhibited much wider optical bandgaps (1.95 eV–2.16 eV) than other reported PDTBF polymers (mostly narrow band gaps: 1.40–1.70 eV), due to the format of linkage between OEG side chains and thiophene units. It is an effective strategy to control the optical properties of the conjugated polymers using OEG side chain engineering investigation.