Crystal Polymorph Control for High-Performance Organic Field-Effect Transistors

Abstract

Organic molecules are assembled together by weak non-covalent intermolecular interactions in solid state. Multiple crystalline packing states (crystal polymorphism) have commonly existed in the active layer for organic field-effect transistors (OFETs). Different polymorphs, even with the slightest changes in their molecular packing, can differ the charge transport mobility by orders of magnitude. Therefore, accessing new polymorphs can serve as a novel design strategy for attaining high device performance. Here, we review the state of the art in this emerging field of crystal polymorph control. We firstly introduce the role of polymorphism and the methods of polymorph control in organic semiconductors. Then we review the latest studies on the performance of polymorphs in OFET devices. Finally, we discuss the advantages and challenges for polymorphism as a platform for the study of the relationship between molecular packing and charge transport.

Improving Charge Mobilities of Novel Push–Pull Small Molecules through Thermally Induced Self‐Ordering

“…Generally, control of molecular packing enable tuning their charge‐transport properties of materials. [ 20,21 ]…”

“…Generally, control of molecular packing enable tuning their charge-transport properties of materials. [20,21] Polarized optical microscopy (POM), atomic force microscopy (AFM), scanning electron microscopy (SEM) measurements, and grazing-incidence wide-angle X-ray scattering (GIWAXS) were further used to investigate the morphology, molecular packing, and self-organization of the materials in solid state before and after annealing. The POM images of BBT-H and BBT-F are obtained with Carl Zeiss Axioscope A1 microscope with crossed polarizers (Figure 4).…”

Template and Temperature-Controlled Polymorph Formation in Squaraine Thin Films

“…Crystalline organic thin films often exhibit linear dichroism and birefringence . By structural design of the molecular building blocks, advanced functionality can be introduced including nonlinear optical properties or circular dichroism. , In addition, fine-tuning can be obtained by selecting a specific polymorph through the processing conditions. − The interest in polymorph selective growth of organic molecules is widespread, because the polymorph choice can determine the color of pigments and aggregates, , improve optoelectronic device performance, − or decide about the biofunctionality of, for instance, active drug ingredients. − Even for monolayer J-aggregates, polymorphism determines the polarized light fluorescence . The dihydroxy anilino squaraine SQIB (2,4-bis­[4-( N , N -diisobutylamino)-2,6-dihydroxyphenyl]­squaraine), as sketched in Figure a, is a prototypical quadrupolar donor–acceptor–donor-type semiconductor compound.…”