Improving Both Electron and Hole Mobilities of an Ambipolar Polymer by Integrating Sodium Sulfonate‐Tethered Alkyl Side Chains†

Abstract

Summary of main observation and conclusionHigh performance ambipolar organic semiconductors are highly desirable for organic logic circuits. Herein, we demonstrate the integration of sodium sulfonate (SS)‐tethered sidechains into a diketopyrrolopyrrole‐based ambipolar polymer (PDPP3T) can simultaneously improve its hole and electron transport performances either parallel or perpendicular to polymer film. Three SS‐functionalized polymers (PDPP3T‐xSS, x = 0.025, 0.05 and 0.10) were synthesized and studied. It was found that SS functionalization can reinforce interchain π‐π interactions, slightly lower frontier orbital energy levels, produce more rod‐like structures in film, and change chain‐packing from edge‐on to face‐on fashion, but has little influence on thermal properties. More interestingly, organic field‐effect transistors reported hole mobility of 0.27 ± 0.066 cm2·V–1·s–1 and electron mobility of 0.038 ± 0.016 cm2·V–1·s–1 for PDPP3T, while increased 2.4 and 5 folds to 0.64 ± 0.087 and 0.19 ± 0.051 cm2·V–1·s–1 for PDPP3T‐0.025SS, respectively. Moreover, PDPP3T‐xSS devices displayed reduced threshold voltages for both hole and electron transports. Meanwhile, space charge‐limited current method found SS functionalization achieved an order of magnitude increase in electron mobility and slight enhancement in hole mobility transporting perpendicular to polymer film. In‐depth investigations suggest such enhancements may originate from the joint actions of chain‐stacking modulation and ionic doping effect.