Preparation of semi‐alternating conjugated polymers using direct arylation polymerization (DArP) and improvement of photovoltaic device performance through structural variation

Abstract

The results herein expand on optimized direct arylation polymerization (DArP) conditions for defect‐free poly[(2,5‐bis (2‐hexyldecyloxy)phenylene)‐alt‐(4,7‐di(thiophen‐2‐yl)benzo[c][1,2,5] thiadiazole)] (PPDTBT). Semi‐alternating and alternating donor–acceptor polymers containing alkoxy phenylene, dithienyl‐substituted thieno[3,4‐c]pyrrole‐4,6‐dione (DTTPD), and dithienyl‐substituted diketopyrrolopyrrole (DTDPP) were prepared via DArP, including a four‐component semi‐alternating copolymer PPDTDPPTPD. Variation of the alkoxy substituents on the phenylene donor including n‐hexyl, 2‐ethylhexyl, or 2‐hexyldecyl allowed for the tuning of thephysical and electronic properties. Molecular weights (Mn) ranged from 3.07 to 28.3 kDa for the PPDTTPD polymers and 2.63‐44.0 kDa for the PPDTDPP polymers, depending on the alkoxy substituents. Absorbance maxima and HOMO energies were varied from 550 to 602 nm and −5.31 to −5.69 eV for the PPDTTPD polymers and from 671 to 794 nm and −5.41 to −5.55 eV for the PPDTDPP polymers, respectively. Additive‐free, bulk heterojunction (BHJ) solar cells were fabricated, and the fill‐factors obtained (0.57–0.63) are some of the highest reported for polymers prepared using DArP. Higher molecular weight polymers for both PPDTTPD (28 kDa) and PPDTDPP (44 kDa) series performed poorly in solar cells. In contrast, the semi‐alternating polymers of lower Mn for the PPDTTPD (12.4 kDa) and PPDTDPP (9.05 kDa) series, incorporating both n‐hexyl and 2‐hexyldecyl alkoxy phenylene donors, provided power conversion efficiencies (PCE) of 3.26% and 3.49%, respectively. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017, 55, 3370–3380

Improving the efficiency and sustainability of catalysts for direct arylation polymerization (DArP)

“…118,131 It would be expected that such approach can be adopted by Ozawaderived DArP conditions, since the catalytic direct arylation cycles for both classes of conditions proceed via a critical CMD transition state (Figure 2), 63 only differentiated by a different ligation of the Pd catalyst. Leclerc et al, 169 Marks et al, 61 and Thompson et al 136,170 successfully demonstrated that the use of bulky carboxylic acid additives can be expanded to Ozawa-derived conditions thereby suppressing the C H activation of undesired positions and preventing the formation of β-defects. Besides the carboxylate ligands, another important ligand coordinated to the Pd center in the Ozawa-derived conditions is the phosphine ligand.…”