Carrier Mobility in Organic Thin-film Transistors: Limiting Factors and Countermeasures

Abstract

Device physics in organic thin-film transistors (OTFTs) have been extensively studied along with the efforts to improve device performance and to develop their applications. Among many promising organic semiconducting materials, pentacene has been a benchmark in this research field. Understanding the bottlenecks of carrier transport in pentacene OTFTs is therefore important to maximize the performance of OTFTs. In this paper, we summarize our knowledge on the bottlenecks against carrier transport in practical polycrystalline organic thin films: extrinsic factors that disturb the carrier transport in OTFTs, intrinsic structure and properties, equations to express the overall carrier mobility in polycrystalline films, and influence of surface chemical modification on the crystallographic and electronic structures.

Temperature Dependence of Transport Properties in dinaphtho[2,3-b:2’,3’-d] thiophene Thin-Film Transistors with MoO₃/Au Electrodes

“…Figure 5 shows possible mechanism of conduction model. For smaller gate voltage, the drain current was proportional to the drain voltage [4], as shown in Fig. 2.…”

“…Temperature dependence of V D -I D characteristics can be explained with two possible charge transport mechanisms which are Schottky thermionic emission and polycrystalline model at ground boundary. [4] In the forward applied voltage V D region, temperature dependence of V D -I D characteristics can be fitted by the Schottky thermal emission mechanism model with barrier height range from 33 to 57 meV, as shown in Fig. 3.…”

“…We will consider a conduction model in C6-DNT-V TFTs. Nakamura et al [4] reported that barrier height of 150 meV at grain boundary, band fluctuation in the domain is 30 meV, and charge transport is explained using polycrystalline model in pentacene TFT. The activation energy of the C6-DNT-V between 33 and 73 meV is originate from the Schottky thermal emission between C6-DNT-V and MoO 3 /Au electrode, where, typical value of mobility was 1.5 cm 2 /Vs with C6-DNT-V thickness of 40 nm.…”

Gate-bias and temperature dependence of charge transport in dinaphtho[2,3-b:2′,3′-d]thiophene thin-film transistors with MoO3/Au electrodes

“…They demonstrated that the charge transport could be explained using a polycrystalline model in a pentacene thin-film transistor. 31) The activation energy of C6-DNT-V (between 33 and 73 meV) originated from the Schottky thermal emission between C6-DNT-V and the MoO 3 =Au electrode, where the typical mobility was 1.1 cm 2 V −1 s −1 with a C6-DNT-V thickness of 40 nm. The mobility decreased to 0.48 cm 2 V −1 s −1 when using only the Au electrode, and the process condition for C6-DNT-V was not changed.…”

Direct x-ray detection using thin-film pentacene Schottky diodes

“…Pentacene is a p-type benchmark material that has been largely studied in the field of organic electronics with relatively better hole mobilities greater than 1 cm 2 /V.s in the thin-film form [49,50]. Thus, with the combined advantages of thin-film grown pentacene and Schottky configuration, in the present work we have fabricated pentacene based photodiode to detect x-rays directly.…”