Charge Carrier Mobility Improvement in Diketopyrrolopyrrole Block-Copolymers by Shear Coating

• Main Authors: Kristina Ditte, Nataliya Kiriy, Jonathan Perez, Mike Hambsch, Stefan C. B. Mannsfeld, Yulia Krupskaya, Ramesh Maragani, Brigitte Voit, Franziska Lissel
• Format: Article
• Language: English
• Published: MDPI AG 2021-04-01
• Series: Polymers
• Subjects: block copolymers; organic field-effect transistors; shear coating; shear speed; thickness-dependent mobility
• Online Access: https://www.mdpi.com/2073-4360/13/9/1435
• ISSN: 2073-4360

Shear coating is a promising deposition method for upscaling device fabrication and enabling high throughput, and is furthermore suitable for translating to roll-to-roll processing. Although common polymer semiconductors (PSCs) are solution processible, they are still prone to mechanical failure upon stretching, limiting applications in e.g., electronic skin and health monitoring. Progress made towards mechanically compliant PSCs, e.g., the incorporation of soft segments into the polymer backbone, could not only allow such applications, but also benefit advanced fabrication methods, like roll-to-roll printing on flexible substrates, to produce the targeted devices. Tri-block copolymers (TBCs), consisting of an inner rigid semiconducting poly-diketo-pyrrolopyrrole-thienothiophene (PDPP-TT) block flanked by two soft elastomeric poly(dimethylsiloxane) (PDMS) chains, maintain good charge transport properties, while being mechanically soft and flexible. Potentially aiming at the fabrication of TBC-based wearable electronics by means of cost-efficient and scalable deposition methods (e.g., blade-coating), a tolerance of the electrical performance of the TBCs to the shear speed was investigated. Herein, we demonstrate that such TBCs can be deposited at high shear speeds (film formation up to a speed of 10 mm s⁻¹). While such high speeds result in increased film thickness, no degradation of the electrical performance was observed, as was frequently reported for polymer−based OFETs. Instead, high shear speeds even led to a small improvement in the electrical performance: mobility increased from 0.06 cm² V⁻¹ s⁻¹ at 0.5 mm s⁻¹ to 0.16 cm² V⁻¹ s⁻¹ at 7 mm s⁻¹ for the TBC with 24 wt% PDMS, and for the TBC containing 37 wt% PDMS from 0.05 cm² V⁻¹ s⁻¹ at 0.5 mm s⁻¹to 0.13 cm² V⁻¹ s⁻¹ at 7 mm s⁻¹. Interestingly, the improvement of mobility is not accompanied by any significant changes in morphology.