Enhancing P3HT/PCBM blend stability by thermal crosslinking using poly(3-hexylthiophene)-S,S-dioxide†
A statistical copolymer containing thiophene and thiophene dioxide, namely poly[(3-hexylthiophene)-co-(3-hexylthiophene-S,S-dioxide)] (P3HT-TDO), was utilized as a thermal crosslinker in a blend of poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl-C60-butyric methyl ester (PCBM), demonstrating an effective strategy for preventing agglomeration of PCBM and enhancing blend stability. P3HT-TDO was synthesized by microwave-assisted oxidation of P3HT and its characterization was carried out using UV-Vis spectroscopy, 1H-NMR, Fourier Transform Infrared Spectroscopy (FTIR), and X-ray Photoelectron Spectroscopy (XPS). Crosslinking of P3HT-TDO was achieved via Diels–Alder reaction at ∼150 °C. Thermogravimetric analysis, combined with FTIR and differential scanning calorimetry, were used to study the crosslinking process. In order to test the impact of thermal cross-linking, field effect transistors (FETs) were fabricated using pristine and compared to cross-linked P3HT. It was found that P3HT-TDO crosslinking did not suppress charge mobility. The stability of the P3HT/P3HT-TDO/PCBM blend was characterized in the solid-state from spin-coated thin films. The samples were analysed using UV-vis spectroscopy and Grazing Incidence X-ray Diffraction (GIXRD) to monitor the effects of thermal processing. The results revealed that presence of P3HT-TDO in the blend minimizes crystallization of PCBM during annealing and preserves the ordered microcrystalline segments from P3HT. Optical microscopy analysis of P3HT/P3HT-TDO/PCBM thin films also confirmed the effectiveness of the strategy and inhibition of PCBM crystal formation even after 155 hours of annealing.