Squaraine‐Based Polymers: Toward Optimized Structures for Optoelectronic Devices

A novel polymer semiconductor based on squaric acid is successfully prepared through polycondensation reaction. Physicochemical properties of polysquaraine are explored by Fourier transform infrared (FT‐IR) and ultraviolet‐visible (UV‐vis) absorption spectroscopy, thermogravimetric/modulated temperature differential scanning calorimetry (TGA/MTDSC) analyses, and cyclic voltammetry (CV). Next, the charge carrier properties are investigated through the fabrication and characterization of field‐effect transistors (FETs) using solution‐processed polymeric films. It is found that the polysquaraine is FET active and exhibits decent p‐type mobilities (up to 5 × 10^?4 cm² V^?1 s^?1), which illustrates the promising properties of this semiconductor in optoelectronics. Notably, there is no precedent for the use of squaraine‐based polymers in field‐effect transistors. Bulk heterojunction solar cells (BHJ‐OSCs) are finally prepared from the blends of polysquaraine with the fullerene derivative 6,6]‐phenyl‐C₇₁‐butyric acid methyl ester (PC₇₁BM). Power conversion efficiencies up to 0.86% are achieved for nonoptimized system under simulated air mass 1.5 (AM1.5) conditions.