Tailoring Crystallization Growth of Small-Molecule Organic Semiconductors by Modification with Conjugated Polymers for Organic Field-Effect Transistors

Abstract

By investigating a typical small molecule, 6,13-bis(triisopropylsilylethynyl) pentacene (TIPS), the crucial influence of conjugated polymers as additives on modulating the crystallization processes, crystalline structures, and carrier transport is unraveled. The conjugated polymer additives including poly[2,5-bis(3-alkylthio-phen-2-yl)thieno(3,2-b)thiophene (PBTTT) and poly(9,9-di-n-octylfluorene-alt-benzothiadiazole) (F8BT) via a solution crystallization method can bring in crystalline structures that are not accessible by nonconjugated polymers, demonstrating superior order and enhanced carrier transport without external treatments. In such cases, polymorphism of the small molecules is manipulated by the features of conjugated polymers in the blend. According to optical microscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray diffraction (XRD), different crystalline morphologies such as fibrous crystals from TIPS/PBTTT and rod-like crystals from TIPS/F8BT are observed, which is determined by the crystalline habitats and solubility of conjugated polymers in small-molecule/polymer blends. Meanwhile, organic field-effect transistors (OFETs) based on TIPS/PBTTT and TIPS/F8BT blends are prepared for the purpose of exploring the electrical characteristics, yielding the mobility of 0.3 and 3.53 cm2 V−1 s−1, respectively. The conjugated-polymer-mediated polymorphism of small molecules can provide an attractive platform to explore the fundamental relationship between crystal stacking and electrical behaviors without altering the chemical structure.