Impact of side‐chain length on the phase structures of P3ATs and P3AT:PCBM films as revealed by SSNMR and FTIR

• Published in: Journal of polymer science. Part B, Polymer physics Vol. 56; no. 9; pp. 751 - 761
• Main Authors: Zhang, Tiantian, Yuan, Yuan, Cui, Xiang, Yin, Hongnan, Gu, Jiali, Huang, He, Shu, Jie
• Format: Journal Article
• Language: English
• Published: Hoboken Wiley Subscription Services, Inc 01.05.2018
• Subjects: blends; Butyric acid; conducting polymer; Crystal structure; Crystallinity; Crystallization; FTIR; Mesophase; NMR; Nuclear magnetic resonance; P3AT; PCBM; phase seperation; Polymer blends; semicrystalline structures; solid‐state NMR
• ISSN: 0887-6266; 1099-0488
• DOI: 10.1002/polb.24587

ABSTRACT It is known that poly(3‐alkylthiophene) (P3AT) side‐chain length notably influences the photovoltaic performances of relating devices. However, comprehensively study on its impact on the structures of P3ATs and their blends with [6, 6]‐phenyl‐C61 butyric acid methyl ester (PCBM) is insufficient. By using solid‐state NMR and FTIR techniques, four P3ATs and their PCBM blends are investigated in this work, focusing on the phase structures as modulated by side‐chain length. Recently, we revealed multiple crystalline main‐chain packings of packing a and b together with a mesophase in poly(3‐butylthiophene) (P3BT) films (DOI: 10.1021/acs.macromol.6b01828). Here, the semicrystalline structures are investigated on poly(3‐hexylthiophene) (P3HT), poly(3‐octylthiophene) (P3OT), and poly(3‐dodecylthiophene) (P3DDT) with traditional form I modification, where packing a and the amorphous phase are probed. Furthermore, crystallized side chain within packing a is detected in both P3OT and P3DDT films, which shows a FTIR absorption at 806 cm−1. Structural studies are also conducted on P3AT:PCBM blends. Compared with the pure P3ATs, the polymer crystallinities of the blends show reduction of about 40% for P3OT and P3DDT, whereas only about 10% for P3HT. Moreover, in P3BT:PCBM and P3HT:PCBM, the crystalline polymers and PCBM are phase separated, while in P3OT:PCBM and P3DDT:PCBM, blend components are mostly miscible. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2018, 56, 751–761 Based on the variable temperature experiments, the 806 cm−1 band, detected in the FTIR spectra of P3OT and P3DDT films, is assigned to the packing a crystalline phase with the crystallized alkyl side chains. Furthermore, according to the correlation signals of frequency‐switched Lee‐Goldburg heteronuclear correlation (FSLG‐HETCOR), it is revealed that in P3BT:PCBM and P3HT:PCBM blends, the crystalline polymers and PCBM are phase separated, while in P3OT:PCBM and P3DDT:PCBM, blend components are mostly miscible.