Dopant Diffusion Inhibition in Organic Field-Effect Transistors Using Organic Semiconductor/High-Molecular-Weight Polymer Blends

Abstract

Molecular contact doping in organic field-effect transistors (OFETs) has been proved to be a very efficient strategy to reduce the device contact resistance. It consists of inserting a dopant layer between the organic semiconductor (OSC) and the top gold contacts to reduce the energy barrier required to inject/ release charges. However, a main bottle-neck for its implementation is that the dopant diffuses toward the OFET channel with time, doping the OSC, and hampering the on/off switching device capability. In this work, we fabricated OFETs based on the benchmark OSC 2,7) by a solution shearing technique. First, we show that the OFET performance of these devices is significantly improved when a layer of the p-dopant 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F 4 TCNQ) is inserted before the evaporation of the gold source/drain contacts. Remarkably, we demonstrate that the dopant diffusion can be controlled by blending the OSC with polystyrene (PS) of different molecular weights. In-depth electrical characterization combined with studies of surface and in-depth distribution of the dopant by time-of-flight secondary ion mass spectrometry (ToF-SIMS) unambiguously show that in thin films of OSC blends with high-molecular-weight PS, the dopant remained drastically confined into the contact areas, which was reflected by an enhanced long-term device stability.

Low-Voltage and Highly Sensitive PbS Quantum Dot Thin-Film X-ray Monitors

“…In Figure j, a 3D distribution of the most characteristic ion signals representing the QD film (S – , m / z = 31.97, blue) and the gold electrodes (Au – , m / z = 196.93, gold) is presented. The three-dimensional chemical distribution of such chemical species provides a comprehensive visualization of the entire device architecture . The data cube illustration reveals that the PbS QDs are efficiently distributed not only onto the surface of the device but also among the interdigitated gold electrodes, ensuring the conditions for efficient charge transport and electron transfer throughout the entire active layer.…”

“…The three-dimensional chemical distribution of such chemical species provides a comprehensive visualization of the entire device architecture. 54 The data cube illustration reveals that the PbS QDs are efficiently distributed not only onto the surface of the device but also among the interdigitated gold electrodes, ensuring the conditions for efficient charge transport and electron transfer throughout the entire active layer. The uniformity of the QDs' distribution is a promising characteristic for achieving high-performance devices as it is expected to increase the charge transport and device stability.…”

Nanoscale Operando Characterization of Electrolyte‐Gated Organic Field‐Effect Transistors Reveals Charge Transport Bottlenecks

“…In this regard, the relatively low transversal conductivity identified in the present study due to the anisotropic molecular packing [ 23,27 ] explains the relatively large series access resistance observed. Resolving the limitation induced by this molecular packing, for example, through molecular contact doping, as recently reported in OFETs, [ 8,30 ] could significantly improve the characteristics of devices based on this semiconducting material. Furthermore, increasing the grain sizes or decreasing the channel length would allow single grains connecting the source and drain electrodes and hence will reduce the impact of grain boundaries, and improve the device performance.…”

“…[6,7] However, understanding the thin film blended microstructure with two components and probing its impact on charge transport in operando across a range of length scales is challenging. Typically, in these blends, the organic semiconductor crystallizes on top of the bottom binding polymer layer, [8,9] while the charge transport layer is confined in a 2D channel top layer at the semiconductor/electrolyte interface, [10] since the semiconducting film is impermeable to ions. Therefore, the morphology and structure of the top layers of the semiconductor in contact with the electrolyte play a key role in the charge transport characteristics of these devices.…”

Evaluating mobility extraction reliability in non-ideal organic transistors utilizing weak epitaxy-grown pentacene films

“…Similarly, electron mobility around 15 cm 2 Vs −1 has been reported in solutionprocessed OTFTs based on the tetrachloro derivative [18]. Furthermore, C8-BTBT films have achieved ultrahigh mobilities by optimizing fabrication conditions and device structures [19][20][21]. Another approach to enhance carrier mobilities involves the use of a small-molecule/polymer blends [22][23][24], which typically induces vertical phase separation, and leverages polymers to facilitate the crystallization of small molecules.…”