Bar‐Coated Organic Thin‐Film Transistors with Reliable Electron Mobility Approaching 10 cm² V⁻¹ s⁻¹

Abstract

Currently, a considerable number of solution-processed high mobility p-type OTFTs have been obtained. [4-8] However, the achievement of high performance n-type OTFTs via solution processing is still challenging, yet important for the construction of organic circuits such as complementary metal-oxide-semiconductor (CMOS)-like circuits. [9-12] Reviewing of recent development has demonstrated that the highest reliable electron mobility from solution-processed OTFTs is 7.16 cm 2 V −1 s −1 to date. [11] To enhance the performance of conjugated polymer-based OTFTs, increasing the molecular order of the semiconductor thin film is an effective method. [13-18] Uniaxial alignment of conjugated polymer backbones can increase mobilities along the alignment direction via preferential intrachain transport. [19-21] Driven by directional flow due to Marangoni and capillary effect, bar coating is a valued solution processing technique to orient conjugated polymers for highly ordered thin films. [13,22-26] Besides, large ordered crystalline domains are generally accompanied by long range order, which is essential for high mobilities due to elongated carrier pathways and reduced grain boundaries. [19,27,28] Therefore, uniaxially aligned films featuring large crystalline domains are mostly desirable. In this work, we used a diketopyrrolopyrrole-based conjugated polymer, P4FTVT-C32, [29] as the semiconductor material, bar coating as the solution processing method for highly oriented films of large crystalline fibers. The corresponding OTFTs are characterized by electron mobility up to 9.38 cm 2 V −1 s −1 in the saturation regime and 8.35 cm 2 V −1 s −1 in the linear regime, and on/off ratio 10 5-10 6. Notably, these mobilities extracted according to the gradual channel approximation model is highly reliable since the devices are close to ideal transistors. This can be reflected by linear fitting of linear regime drain current and the square root of saturation regime drain current against gate voltage, the resulted independence of mobility on gate voltage, small gap between linear and saturation mobility, and high reliability factor >80%. To the best of our knowledge, these are the record high saturation and linear mobilities of n-type OTFTs, taking into account of the reliability.

Unraveling the Molar Mass Dependence of Shearing‐Induced Aggregation Structure of a High‐Mobility Polymer Semiconductor

“…The degree of polymer alignment has proven to have a strong dependence on the coating speeds, and thus a remarkable enhancement in charge-transport anisotropy can be achieved. [24][25][26][27][28] Moreover, the choice of solvent plays an important role in determining device performance as well. Many previous reports have demonstrated the formation of uniaxially aligned nanofibrillar film morphologies by utilizing certain (mixture) solvents Aggregation-structure formation of conjugated polymers is a fundamental problem in the field of organic electronics and remains poorly understood.…”

Modification of Indium Tin Oxide Surface with HCl for Source/Drain Electrodes in Organic Thin Film Transistors

“…Based on high conductivity and high surface work function (WF), Au electrodes are beneficial to the outstanding performance of p-type OTFTs, and in some reports, modified Au electrodes are even used in n-type OTFTs. [7][8][9] However, it is well known that Au electrodes are extremely expensive, which would greatly hinder the development of practical applications.Indium tin oxide (ITO), the most commonly used organic light-emitting diodes (OLEDs) anode material, has high conductivity and relatively cheap price, while its work function (≈4.7 eV) is lower than the ionization potentials of most p-type OSC. [10] To reduce the barrier height and facilitate the hole injection, various ITO modification methods have been made in OLEDs and organic photovoltaics (OPVs), such as self-assembling, plasma treatment, ultraviolet (UV)-ozone treatment, surface doping and so on.…”

Diketopyrrolopyrrole-based conjugated polymers synthesized by direct arylation polycondensation for anisole-processed high mobility organic thin-film transistors

“…It has been demonstrated that PEIE modification can effectively lower the work function of Au, and then facilitate efficient electron injection and block the hole injection from electrodes to the semiconducting layer. 70,71 Accordingly, all OTFTs with PEIE interlayer exhibited pure electron transport characteristics with much lower V T (Fig. 3 and Fig.…”