Organic Semiconductors with Benzoic Acid Based Additives for Solution-Processed Thin Film Transistors

Background: although solution-processed small molecular organic semiconductors have attracted great attention for organic electronic applications,the intrinsic crystal misorientation of the organic semiconductorsstill remains as a challenging issue. Objective: two benzoic acid-based additives, i.e. 4-propylbenzoic acid (RBA) and 4-octylbenzoic acid (OBA), were employed to regulate the crystal growth and charge transport of organic semiconductors. Methods: RBA and OBA were mixed with a π-conjugated organic semiconductor 6,13-bis(triisopropylsilylethynyl) pentacene (TIPS pentacene), respectively. Organic thin film transistors (OTFTs) with different bottom-gate, top-contact and bottom-gate, bottom-contact configurations were fabricated to investigate charge transport. Results: RBA and OBA share a similar benzoic acid structure with the same hydrophilic head but differ in the length of hydrophobic tail. The benzoic acid-based additive forms a stratified self-assembled interfacial layer and maneuvers nucleation seed distribution via synergetic interactions with the silanol groups on silicon dioxide and with the bulky side chains of the semiconductor. The TIPS pentacene film with OBA additive exhibited a 10-fold reduction in misorientation angle, as compared to the counterpart with RBA. Conclusion: Distinct thin film morphology in terms of crystal alignment and grain width was observed and correlated to the hydrophobic tail length. In particular,OTFTs incorporating the TIPS pentacene/benzoic acid mixture as the active layer showed a mobility of up to 0.15 cm2/Vs.