Impact of Molecular\nWeight on Microstructure and Carrier\nMobility in Poly(dithienofluorene-<i>alt</i>-dithienodiketopyrrolopyrrole)

The synthesis of three poly(dithienofluorene-<i>alt</i>-dithienodiketopyrrolopyrrole) polymers, PDTFDPP-H with\nan average\nmolecular weight (<i>M</i><sub>n</sub>) of 77 kg mol<sup>–1</sup>, PDTFDPP-M with an <i>M</i><sub>n</sub> of 28 kg mol<sup>–1</sup>, and PDTFDPP-L with an <i>M</i><sub>n</sub> of 11 kg mol<sup>–1</sup>, has been\naccomplished. UV–vis spectroscopy reveals a shoulder at 780\nnm for PDTFDPP-H, indicating potential polymer aggregation. Solvent-\nand temperature-variable UV–vis absorption spectra, coupled\nwith DFT calculations, support this observation. Hole mobility (μ<sub>h</sub>) follows the sequence PDTFDPP-H (0.305 cm<sup>2</sup> V<sup>–1</sup> s<sup>–1</sup>) > PDTFDPP-M (1.88 ×\n10<sup>–3</sup> cm<sup>2</sup> V<sup>–1</sup> s<sup>–1</sup>) > PDTFDPP-L (5.19 × 10<sup>–4</sup> cm<sup>2</sup> V<sup>–1</sup> s<sup>–1</sup>). Grazing\nincidence X-ray scattering\nreveals that PDTFDPP-L and PDTFDPP-M primarily exhibit edge-on crystallites,\nwhile PDTFDPP-H displays both edge-on and face-on crystallites, all\ndemonstrating short-range π-order. The formation of edge-on\nor face-on crystallites seems to correlate with the polymer molecular\nweight. Transmission electron microscopy analysis of PDTFDPP-H reveals\nchain entanglement. Overall, the results suggest that the PDTFDPP-H\naggregates are interconnected with the help of one-dimensional polymer\nchains, achieving a μ<sub>h</sub> higher than 0.1 cm<sup>2</sup> V<sup>–1</sup> s<sup>–1</sup>.