End Capping Does Matter: Enhanced Order and Charge Transport in Conjugated Donor-Acceptor Polymers

Optimized microstructure through control of both intra- and intermolecular interactions in organic semiconductors is critical for enhancing and optimizing charge transport for the realization of next-generation low-cost, mechanically flexible, and easy to process high performance, organic field effect transistors (OFETs). Herein, we report donor-acceptor alternating copolymers of dithienogermole (DTG) with 2,1,3-benzothiadiazole (BTD) and probe the importance of end groups on the control of molecular order and microstructure as it relates to the enhancement of charge carrier transport. Partial end-capping reactions, confirmed by ¹H NMR and matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) analyses, on the DTG-BTD copolymer provided significant improvement in grazing incidence wide angle X-Ray scattering (GIWAXS) determined polymer ordering in thin films. Consequently, OFETs exhibited charge-carrier mobilities up to 0.60 cm²/(Vs) for the end-capped copolymer, which are an order of magnitude higher in comparison to the non-end-capped analogue, which displayed a mobility of 0.077 cm²/(Vs). We emphasize that a simple synthetic approach, the introduction of end-capping groups which remove reactive functionalities, can be effective in the development of next-generation OFET and solar materials by promising better control of the polymer organization.