Buta-1,3-diyne-Based π-Conjugated Polymers for Organic Transistors and Solar Cells

We report the synthesis and characterization of new alkyl-substituted 1,4-di(thiophen-2-yl)buta-1,3-diyne (R-DTB) donor building blocks, based on the −CC-CC- conjugative pathway, and their incorporation with thienyl-diketopyrrolopyrrole (R'-TDPP) acceptor units into π-conjugated PTDPP-DTB polymers (P1-P4). The solubility of the new polymers strongly depends on the DTB and DPP solubilizing (R and R', respectively) substituents. Thus, solution processable and high molecular weight PDPP-DTB polymers are achieved for P3 (R = n-C₁₂H₂₅, R' = 2-butyloctyl) and P4 (R = 2-ethylhexyl, R' = 2-butyloctyl). Systematic studies of P3 and P4 physicochemical properties are carried using optical spectroscopy, cyclic voltammetry, and thermal analysis, revealing characteristic features of the dialkynyl motif. For the first time, optoelectronic devices (OFETs, OPVs) are fabricated with 1,3-butadiyne containing organic semiconductors. OFET hole mobilities and record OPV power conversion efficiencies for acetylenic organic materials approach 0.1 cm²/(V s) and 4%, respectively, which can be understood from detailed thin-film morphology and microstructural characterization using AFM, TEM, XRD, and GIWAXS methodologies. Importantly, DTB-based polymers (P3 and P4) exhibit, in addition to stabilization of frontier molecular orbitals and to −CC-CC- relief of steric torsions, discrete morphological pliability through thermal annealing and processing additives. The advantageous materials properties and preliminary device performance reported here demonstrate the promise of 1,3-butadiyne-based semiconducting polymers.