Vertically Segregated Structure and Properties of Small Molecule–Polymer Blend Semiconductors for Organic Thin‐Film Transistors

Abstract

A comprehensive structure and performance study of thin blend films of the small‐molecule semiconductor, 2,8‐difluoro‐5,11‐bis(triethylsilylethynyl)anthradithiophene (diF‐TESADT), with various insulating binder polymers in organic thin‐film transistors is reported. The vertically segregated composition profile and nanostructure in the blend films are characterized by a combination of complementary experimental methods including grazing incidence X‐ray diffraction, neutron reflectivity, variable angle spectroscopic ellipsometry, and near edge X‐ray absorption fine structure spectroscopy. Three polymer binders are considered: atactic poly(α‐methylstyrene), atactic poly(methylmethacrylate), and syndiotactic polystyrene. The choice of polymer can strongly affect the vertical composition profile and the extent of crystalline order in blend films due to the competing effects of confinement entropy, interaction energy with substrate surfaces, and solidification kinetics. The variations in the vertically segregated composition profile and crystalline order in thin blend films explain the significant impacts of binder polymer choice on the charge carrier mobility of these films in the solution‐processed bottom‐gate/bottom‐contact thin‐film transistors.

Thickness-dependent electrical properties of soluble acene–polymer blend semiconductors

“…Electrical characterization of OFETs based on diF-TES-ADT/PMMA blend films indicates that the morphology and thickness of diF-TES-ADT crystals are critical factors for obtaining high field-effect mobility. The obtained field-effect mobility of 0.1 cm 2 /V s at the concentration of 20 mg/ml is similar to the recent reports by Kim et al and Shin et al, which used diF-TES-ADT/poly(a-methylstyrene) as active layer in bottom-gate/bottom-contact OFETs [5,11]. However, when diF-TES-ADT was blended with amorphous conjugate polymer such as poly(triarylamine) or poly(dialkyl-fluorene-co-dime thyl-triarylamine), field-effect mobility greater than 5 cm 2 /V s was reported [34].…”

“…Because charge transport occurs at the dielectric/semiconductor interface laterally, the conducting pathway from the source to drain electrode should be well-defined. Therefore, inducing vertical phase separation is an effective method for obtaining high mobility in OFETs [5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21]. For example, it has been demonstrated that a phase-separated structure comprising an insulating polymer top layer and an organic semiconductor bottom layer-poly(methyl methacrylate) (PMM A)-top/poly(3-hexylthiophene) (P3HT)-bottom-increases environmental stability in bottom-gate/bottom-contact OFETs [6].…”

High mobility transistors based on electrospray-printed small-molecule/polymer semiconducting blends

“…The strong absorption located at 307 nm is attributed to the B1A1 electronic transition that is polarized along the long axis of the conjugated core, whereas the broad absorption at the range 350-400 nm is attributed to the PTAA. In addition, the lower absorption at 550 nm is attributed to the A1A1 electronic transition polarized along the short axis of the conjugated core [22]. The spectra consistency with previous reported values of diF-TES-ADT and PTAA highlights the potentiality of this process to develop high quality semiconducting films.…”

The Influence of Isomer Purity on Trap States and Performance of Organic Thin‐Film Transistors

“…Such separation is also encouraged by the polarity and hydrophilicity of the SiO 2 surface, which favors assembly of the more polar syn -isomer molecules. [37] …”