Vertical Phase Separation in Small Molecule:Polymer Blend Organic Thin Film Transistors Can Be Dynamically Controlled

Abstract

Abstract:Blending of small-molecule organic semiconductors (OSCs) with amorphous polymers is known to yield high performance organic thin film transistors (OTFTs). Vertical stratification of the OSC and polymer binder into well-defined layers is crucial in such systems and their vertical order determines whether the coating is compatible with a top and/or a bottom gate OTFT configuration. Here, we investigate the formation of such blends prepared via spincoating in conditions which yield bilayer and trilayer stratifications, and use a combination of experimental and computational tools to study the competing effects of formulation thermodynamics and process kinetics in mediating the final vertical stratification. We show that trilayer stratification (OSC/polymer/OSC) is the thermodynamically favored configuration and that formation of the buried OSC layer can be kinetically inhibited in certain conditions of spincoating, resulting in a bilayer stack instead. Our analysis reveals that preferential loss of the Zhao et al., Adv. Func. Mater. 2016 2 OSC, combined with early aggregation of the polymer phase due to rapid drying, inhibit the formation of the buried OSC layer. We then moderate the fluid dynamics and drying kinetics during spin-coating to promote trilayer stratification with a high quality buried OSC layer which yields unusually high mobility >2 cm 2 V -1 s -1 in the bottom-gate top-contact configuration.

Effective Use of Electrically Insulating Units in Organic Semiconductor Thin Films for High‐Performance Organic Transistors

“…On the other hand, the PS, PαMS, and PTAA blends often form trilayer structure a polymer layer sandwiched between top and bottom small molecule OSC layers. [209] As a result of many efforts expended on this blend approach, diF-TES-ADT FETs with charge-carrier mobility values greater than 5 cm 2 V −1 s −1 have recently been reported, which is comparable to the result for a single-crystal device using the same material. Shin and coworker demonstrated the migration of diF-TES-ADT molecules toward the polar substrate to be driven by entropy rather than enthalpy.…”

Crossover from band-like to thermally activated charge transport in organic transistors due to strain-induced traps

“…We further tested our hypothesis by inserting an ultrathin layer (∼10 nm) of polystyrene between the organic semiconductor film and the SiO 2 dielectric by blending the semiconductor with polystyrene, which can spontaneously stratify into bilayer structures during solution processing with the polystyrene layer buried between the semiconductor and SiO 2 (46,60,61). The polystyrene layer has a CTE of 72 ppm/K (62), which is very similar to the CTE of the organic semiconductor incorporated in these devices (diF-TES ADT, CTE =162 ppm/K), yielding an ITEM of 2.3.…”

Solution‐Processed Wide‐Bandgap Organic Semiconductor Nanostructures Arrays for Nonvolatile Organic Field‐Effect Transistor Memory

“…By tuning these relevant parameters, many possible morphologies can be made from the phase separation. Various phase‐separated morphologies have been applied in organic electronics, such as OFETs, OLEDs, organic photovoltaic solar cells (OPVs), etc., to improve device performance . Motivated by the previous research in phase‐separated microstructures, we are interested in developing isolated charge trapping sites using WBG organic semiconductor materials by phase separation from spin‐coating blend solutions.…”