Abstract
In the past three decades, organic semiconductor field-effect transistors (OFETs) have drawn intense attentions as promising candidates for drive circuits of flat panel display, radio frequency identifications, chemical/bio-sensors and other devices. Generally, the key parameters of OFETs, carrier mobility, threshold voltage and on/off current ratio, are closely related to the degree of order and surface/interface electronic structure of organic semiconductor (OSC) films. The ordering of the films is crucially determined by the molecule-substrate interactions. On inert substrates (such as SiO2) OSC films can hardly reach high order of degree without growth templates, while traditional single crystal surfaces usually force the OSC molecules deviate their favorite assemble manner resulting in an unstable structure. Recently, the rise of two-dimensional materials (2D) provides a possible solution. The in-plane lattice of 2D materials can offer possible epitaxy templates for OSCs while the weak van der Waals (vdWs) interaction between OSC and 2D layers allows more flexibility to realize the epitaxy growth of OSCs with their favored assemble manner. In addition, the various band structures tuned by layer numbers of 2D materials encourage widely modified OSC electronic structures by interface doping between the OSC and 2D layers, which benefits to obtain high-performance OFETs. In this review, we emphasize and discuss the recent advances of OSC-2D hybrid OFETs. The OSC-2D heterostructures not only promote the OFET device performances by film morphology/structure optimization and channel electronic structure modification, but also offer platforms for basic organic solids physics investigations and further functional optoelectronic devices.
Highlights
Organic semiconductors (OSCs) based on π-conjugated small molecules and polymers has drawn tremendous attention since the 1980s as they show some distinctive characters and advantages compared to the traditional inorganic semiconductors composed of elements from groups III to V, such as ease of large-area fabrication, tunable opto-electronic properties by chemical structure modulation, low cost and power consumption, abundant selection of materials, and capacity for flexible or biocompatible devices (Forrest, 2004; Coropceanu et al, 2007)
The review mainly introduces and summarizes the progress of three types of OSC/2D hybrid FETs according to the role of the 2D materials: (i) 2D materials work as growth templates for the highly ordered OSC layers; (ii) 2D materials are employed to optimize the electronic structure of the OSC conductive channels; and (iii) OSC/2D heterojunction FETs in which the band structures of the heterojunctions endow the device with specific opto-electronic functions, and some fundamental investigations on organic solid physics by OSC/2D heterostructures will be included in this part
As new classes of semiconductor materials have emerged in recent decades, besides the conventional opto-electronic applications, both OSCs and 2D materials show great potential in being applied to the novel smart devices proposed lately, such as wearable or bio-electronic devices, and the combination of OSCs and 2D materials could be a more promising candidate for such demands
Summary
Organic semiconductors (OSCs) based on π-conjugated small molecules and polymers has drawn tremendous attention since the 1980s as they show some distinctive characters and advantages compared to the traditional inorganic semiconductors composed of elements from groups III to V, such as ease of large-area fabrication, tunable opto-electronic properties by chemical structure modulation, low cost and power consumption, abundant selection of materials, and capacity for flexible or biocompatible devices (Forrest, 2004; Coropceanu et al, 2007). The 2D material family (Figure 1) covers a large electrical range from dielectric (such as hexagonal boron nitride, h-BN), semiconducting (such as transition metal dichalcogenides, TMDCs), and metallic (such as graphene), and the band structures can be modulated by the layer numbers (Butler et al, 2013; Novoselov et al, 2016) Such abundant electronic properties are beneficial to tailor the electronic structure of OFETs, optimize the charge carrier concentration, trap density or interface dipoles, and improve device performances. Large-scale highly ordered OSC layers with low defects and OSC/2D heterojunctions with various electronic structures offer perfect platforms for fundamental physics study of OSCs. we emphasize on the recent progress of OFETs based on OSC/2D heterostructures from materials, film growth, electronic structure optimization, and device performance to gain a full view of the OSC/2D hybrid FETs. It is worth noting that OSC/2D heterostructures show their potential in applications for many different kinds of organic optoelectronic
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