Impact of Molecular Weight on Microstructure and Carrier Mobility in Poly(dithienofluorene-alt-dithienodiketopyrrolopyrrole)

Abstract

The synthesis of three poly(dithienofluorene-altdithienodiketopyrrolopyrrole) polymers, PDTFDPP-H with an average molecular weight (M n ) of 77 kg mol −1 , PDTFDPP-M with an M n of 28 kg mol −1 , and PDTFDPP-L with an M n of 11 kg mol −1 , has been accomplished. UV−vis spectroscopy reveals a shoulder at 780 nm for PDTFDPP-H, indicating potential polymer aggregation. Solvent-and temperature-variable UV−vis absorption spectra, coupled with DFT calculations, support this observation. Hole mobility (μ h ) follows the sequence PDTFDPP-H (0.305 cm 2 V −1 s −1 ) > PDTFDPP-M (1.88 × 10 −3 cm 2 V −1 s −1 ) > PDTFDPP-L (5.19 × 10 −4 cm 2 V −1 s −1 ). Grazing incidence X-ray scattering reveals that PDTFDPP-L and PDTFDPP-M primarily exhibit edge-on crystallites, while PDTFDPP-H displays both edge-on and face-on crystallites, all demonstrating short-range π-order. The formation of edge-on or face-on crystallites seems to correlate with the polymer molecular weight. Transmission electron microscopy analysis of PDTFDPP-H reveals chain entanglement. Overall, the results suggest that the PDTFDPP-H aggregates are interconnected with the help of one-dimensional polymer chains, achieving a μ h higher than 0.1 cm 2 V −1 s −1 .