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 via microwave-assisted oxidation of P3HT and its characterization was carried out using UV-Vis spectroscopy, 1H-NMR, and Fourier Transform Infrared Spectroscopy (FTIR). The amount of SO2 groups was estimated by X-ray Photoelectron Spectroscopy (XPS). Crosslinking of P3HT-TDO was achieved via Diels-Alder reaction at temperatures around 150 °C. Thermogravimetric Analysis, combined with FTIR and Differential Scanning Calorimetry, were used to study the crosslinking process. The crosslinking reaction was exothermic above 150 °C and was accompanied by the release of SO2. Filed effect transistors (FETs) fabricated from pristine and cross-linked P3HT confirmed that P3HT-TDO crosslinking did not supress charge mobility. The stability of the P3HT/ P3HT-TDO /PCBM blend was characterized in the solid-state by producing spin-coated thin films; after thermal treatment samples were analysed using UV-vis spectroscopy and Grazing Incidence X-ray Diffraction (GIXRD). The results revealed that presence of P3HT-TDO in the blend minimizes crystallization of PCBM during annealing and preserves the crystal packing motif of P3HT. Optical microscopy analysis of P3HT/ P3HT-TDO /PCBM thin films also demonstrated the effectiveness of the strategy and inhibition of PCBM crystal formation even after 155 hours of annealing.