Influence of the molecular weight in P3HT block on fully conjugated block copolymers

All-conjugated donor-acceptor block copolymers (BCP) were synthesized in a one-pot reaction by a Stille coupling polycondensation through a terminal functional polymer copolymerization process. Mono bromo end-functionalized P3HT samples with various molecular weights (P3HT-Br, M_n: 5, 9, and 26 kg/mol) were copolymerized with AA (N,Nʹ-Bis(2-decyl-1-tetradecyl)-2,6-dibromonaphthalene-1,4,5,8-tetracarboxylic acid bisimide, NDI) and BB (5,5′-bis(trimethylstannyl)-2,2′-bithiophene) type monomers. Further purification by preparative GPC removed excess P3HT to yield block copolymers of low polydispersities with different donor and acceptor block chain lengths. The block copolymers were characterized by ¹H-NMR and UV–vis absorption and FTIR spectroscopy. The optical properties, film morphologies, and optoelectronic properties of the block copolymer were strongly influenced by the donor and acceptor block chain lengths. Furthermore, the fully conjugated D-A block copolymer films exhibited fine structures, smooth film morphologies, and better OPV performance than those features of P3HT/PNDIT2 polymer blends. In polymer solar cells based on the various block copolymer as active layers, the device power convention efficiency was improved by maintaining the acceptor block content at 40–50 kg/mol and increasing the P3HT chain from 5 to 26 kg/mol.