Understanding the Meniscus‐Guided Coating Parameters in Organic Field‐Effect‐Transistor Fabrications

Abstract

Meniscus-guided coating (MGC) is mainly applicable on the soluble organic semiconductors with strong π-π overlap for achieving single-crystalline organic thin films and high-performance organic field-effect-transistors (OFETs). In this work, four elementary factors including shearing speed (v), solute concentration (c), deposition temperature (T), and solvent boiling point (T b ) are unified to analyze crystal growth behavior in the meniscus-guided coating. By carefully varying and studying these four key factors, it is confirmed that v is the thickness regulation factor, while c is proportional to crystal growth rate. The MGC crystal growth rate is also correlated to latent heat (L) of solvents and deposition temperature in an Arrhenius form. The latent heat of solvents is proportional to T b . The OFET channels grown by the optimized MGC parameters show uniform crystal morphology (Roughness R q < 0.25 nm) with decent carrier mobilities (average µ = 5.88 cm 2 V −1 s −1 and highest µ = 7.68 cm 2 V −1 s −1 ). The studies provide a generalized formula to estimate the effects of these fabrication parameters, which can serve as crystal growth guidelines for the MGC approach. It is also an important cornerstone towards scaling up the OFETs for the sophisticated organic circuits or mass production.

Key role of the meniscus shape in crystallization of organic semiconductors during meniscus-guided coating

“…As shown in Fig. 1f, the evaporation regime is established for deposition speeds from 10 mm s À1 to 80 mm s À1 , characterized by a power-law decrease (exponent À1) in film thickness corresponding to observations during blade coating of C8-BTBT, 33 while the mixed regime is found between 200 mm s À1 and 1000 mm s À1 . 11 Interestingly, in the evaporation regime of ADDC, the film thickness is greatly influenced by a.…”

“…14,35 Similar types of morphologies were observed for C8-BTBT by varying the boiling point of the solvent during blade coating. 33 Aligned crystalline ribbons result from balanced-mass-transport at appropriate dipcoating speed and a, as highlighted by the red frame of the corresponding optical microscopy images in Fig. 2 and Fig.…”

“…As previously reported for blade-coating, the amount of molecules per unit volume supplied to the meniscus-line region can be also increased by the solute concentration. 33 The crystalline C8-BTBT films obtained at different dip-coating speeds and a exhibit distinct morphologies, such as crystalline dots, dendrites, ribbons, and slip-stick structures (Fig. 2).…”

Crystallized Monolayer Semiconductor for Ohmic Contact Resistance, High Intrinsic Gain, and High Current Density

“…Third, the considerably lower interlayer adhesion compared with intralayer π-π overlapping allows the formation of crystals with high aspect ratio, e.g., 1L-and 2L-crystals, while under low-speed shearing and well controlled solvent evaporation as presented in our previous work. [20][21][22] With precise control of the temperature (from 60 to 65 °C) and the shearing speed (from 2 to 3 µm s −1 ), the 1L-and 2L-crystals with singlecrystalline domains extending over several millimeters can be achieved. The structural information of the 1L-crystals was measured by X-ray reflectivity (XRR) and is shown in Figure 1a.…”

Impact of p-type doping on charge transport in blade-coated small-molecule:polymer blend transistors

“…5,9,10,[19][20][21][22][23] The drying kinetics during solution-phase deposition is known to strongly influence the morphology, crystallinity and microstructure of the resulting layers, ultimately dictating the charge transport properties of the formed OSC films and their devices. 5,[23][24][25][26][27][28] Though meniscus guided techniques have been used in the past to deposit OSC films with aim to understand the structure-property-performance relationship for OTFTs, 27,[29][30][31][32][33][34] the majority of these studies relied on low to medium coating speeds. 27 In recent years, molecular doping of OSCs has emerged as promising method to enhance the performance of solutionprocessed OTFTs.…”