Direct Uniaxial Alignment of a Donor-Acceptor Semiconducting Polymer Using Single-Step Solution Shearing

Area of Science:

• Materials Science
• Organic Electronics
• Polymer Science

Background:

• Organic semiconductors (OSCs) require alignment for improved electronic device performance, including charge transport and light interaction.
• Aligning polymeric OSCs from solution typically needs complex surface templating or multi-step processing.
• Single-step solution processing for aligned polymeric OSCs remains a key goal in organic electronics.

Purpose of the Study:

• To investigate solution shearing as a single-step method for aligning poly(diketopyrrolopyrrole-terthiophene) thin films.
• To control the degree of polymer alignment by adjusting coating speed during solution shearing.
• To understand the relationship between processing parameters and polymer alignment in thin films.

Main Methods:

• Solution shearing was employed to deposit poly(diketopyrrolopyrrole-terthiophene) thin films.
• Coating speed was systematically varied to tune the degree of polymer alignment.
• Dichroic ratio and X-ray diffraction were used to quantify polymer alignment.
• Film morphology and crystallite size were analyzed.

Main Results:

• A maximum dichroic ratio of approximately 7 was achieved on unpatterned substrates using solution shearing.
• Polymer alignment was found to be dependent on the interplay between solution shear forces and thin film drying dynamics.
• No charge transport anisotropy was observed due to small crystallite size and meshlike morphology.
• X-ray diffraction indicated alignment of polymer molecules in both crystalline and amorphous regions.

Conclusions:

• Solution shearing offers a viable one-step method for tuning the alignment of polymeric OSCs without substrate patterning or post-processing.
• The degree of alignment can be controlled by adjusting shear speed, temperature, and substrate treatment.
• While morphological anisotropy was not observed, molecular alignment was confirmed, suggesting potential for future device optimization.