Here we summarize recent progress in the development of electrolyte-gated transistors (EGTs) for organic and printed electronics. EGTs employ a high capacitance electrolyte as the gate insulator; the high capacitance increases drive current, lowers operating voltages, and enables new transistor architectures. Although the use of electrolytes in electronics is an old concept going back to the early days of the silicon transistor, new printable, fast-response polymer electrolytes are expanding the potential applications of EGTs in flexible, printed digital circuits, rollable displays, and conformal bioelectronic sensors. This report introduces the structure and operation mechanisms of EGTs and reviews key developments in electrolyte materials for use in printed electronics. The bulk of the article is devoted to electrical characterization of EGTs and emerging applications.

Electrolyte-gated transistors for organic and printed electronics

2.2. Interface Trapping Effects 211 3. High-k Dielectric Materials for OFETs 212 3.1. Inorganic Dielectrics 212 3.1.1. Aluminum Oxide 213 3.1.2. Tantalum Oxide 215 3.1.3. Titanium Dioxide 216 3.1.4. Hafnium Dioxide 217 3.1.5. Zirconium Dioxide 218 3.1.6. Cerium Dioxide 218 3.2. Organic Dielectrics 218 3.2.1. Polymer Dielectrics 218 3.2.2. Self-Assembled Monoand Multilayers 225 3.3. Hybrid Dielectrics 227 3.3.1. Polymeric-Nanoparticle Composites 227 3.3.2. Inorganic-Organic Bilayers 232 3.3.3. Hybrid Solid Polymer Electrolytes 235 4. Summary 235 5. Acknowledgments 236 6. References 236

High-k organic, inorganic, and hybrid dielectrics for low-voltage organic field-effect transistors.

Efficiency is crucial for organic light emitting diodes (OLEDs) to be energy-saving and to have a long lifetime for display and solid state lighting applications. Numerous approaches have been proposed to attain high efficiency OLEDs through the synthesis of novel organic materials, the design of light extraction structures and the design of efficiency-effective device architectures. In this report, we first summarise the efficiency records of OLED devices using fluorescent, phosphorescent, and thermally activated delay fluorescent materials. Importantly, we review all the available efficiency-effective device architectural approaches, which include using thin layer structures, low carrier injection barriers, high carrier mobility, balanced carrier injection, effective carrier confinement, effective host-to-guest energy transfer, effective recombination zone, effective exciton generation on the host, effective exciton confinement, p–i–n structures, and tandem structures. It is hoped that better device structures can therefore be devised upon suitable device engineering to achieve higher efficiency for OLED devices.

Approaches for fabricating high efficiency organic light emitting diodes

The present review rationalizes the information spread in the literature concerning the use and role of buffer layers in polymer solar cells. Usual device structures include buffer layers, both at the anode and at the cathode interface, mainly to favour charge collection and extraction, but also to improve the device’s overall performance. Buffer layers are actually essential for achieving highly efficient polymer solar cells and can no more be considered as “optional”, thus the need and importance of understanding their properties and role. The aim of this review is to give the reader an overview of this topic and to provide a practical and useful tool for the daily activities of researchers in the field of polymer photovoltaics.

The role of buffer layers in polymer solar cells

In response to the demands for energy and the concerns of global warming and climate change, energy efficient and environmentally friendly solid-state lighting, such as white light-emitting diodes (WLEDs), is considered to be the most promising and suitable light source. Because of their small size, high efficiency, and long lifetime, WLEDs based on colloidal semiconductor nanocrystals (or quantum dots) are emerging as a completely new technology platform for the development of flat-panel displays and solid-state lighting, exhibiting the potential to replace the conventionally used incandescent and fluorescent lamps. This replacement can cut the ever-increasing level of energy consumption, solve the problem of rapidly depleting fossil fuel reserves, and improve the quality of the global environment. In this review, the recent progress in semiconductor-nanocrystals-based WLEDs is highlighted, the different approaches for generating white light are compared, and the benefits and challenges of the solid-state lighting technology are discussed.

Semiconductor-nanocrystals-based white light-emitting diodes.

The properties of pentacene-based organic thin film transistors (OTFTs) with polymethylmetha-crylate (PMMA) as a dielectric layer have been investigated. The concentration of PMMA was about 8wt% with toluene as solvent. The pentacene film on PMMA dielectric layer displays high thin film quality according to results of x-ray diffraction scan and atomic force microscopy. The crystalline size was about 33.96nm and the grain size was about 1000–1500nm. The pentacene-based OTFTs with PMMA as a dielectric layer exhibited excellent electric characteristics, including a high mobility of 0.241cm2∕Vs or larger, an on/off current ratio of 104 or larger, and the threshold voltage of less than −6.3V.

/pdf/study-of-organic-thin-film-transistor-with-4uikkkekqm.pdf

Study of organic thin film transistor with polymethylmethacrylate as a dielectric layer

The authors have demonstrated the hybridization of polyfluorene (PFO) polymer light-emitting diodes with CdSe-ZnS core/shell quantum dots (QDs) in different device structures. To achieve white light emission, the green and red QDs have been incorporated into the PFO as the single emissive layer. Furthermore, the whole structures were also optimized to engineer the emission spectra. Accordingly, the incorporation of QDs increased the turn-on voltage from 10 to 23 V in device with the blend ratio of PFO : green QD : red QD being 6 : 1 : 1, while the maximum brightness was dramatically decreased.

Three-Band White Light-Emitting Diodes Based on Hybridization of Polyfluorene and Colloidal CdSe–ZnS Quantum Dots

The properties of pentacene-based organic thin film transistors (OTFTs) with poly(methyl methacrylate) (PMMA) as a dielectric layer have been investigated. Toluene was the best solvent for PMMA and the concentration of PMMA was about 8 wt % in toluene. The dielectric constant of PMMA dissolved in toluene was about 2.3. The pentacene film on the PMMA dielectric layer displayed high thin-film quality according to results of atomic force microscopy. The average grain size and surface roughness of pentacene grown on PMMA were about 0.29 µm2 and 10.26 nm, respectively. The pentacene-based OTFTs with PMMA as a dielectric layer exhibited excellent electric characteristics, including a high mobility of 0.241 cm2 V-1 s-1 or larger, an on/off current ratio of 2×104 or larger, and a threshold voltage of less than -5.6 V.

https://iopscience.iop.org/article/10.1143/JJAP.47.3185/pdf

Poly(methyl methacrylate) Dielectric Material Applied in Organic Thin Film Transistors

A nondoped organic system of fullerene (C60)/pentacene was investigated as a connecting unit for green electroluminescent tandem organic light emitting devices with two identical emissive units consisting of (N,N'-di(naphthalene-1-yl)-N,N'-diphthalbenzidine)/tris(8-hydroxyquinoline aluminum) (Alq 3 ) that exhibited better current efficiency and current density characteristics over conventional devices. At 20 mA/cm 2 , the current efficiency of the tandem devices using a nondoped organic layer of C60/pentacene was about 3.4 cd/A, almost 34% improvement over that of the corresponding conventional devices. The connecting unit showed a superior optical transparency, resulting in a minimal microcavity effect in the devices. Interface dipole and band bending on both sides of the C60/pentacene interface was suggested for the formation of an intrinsic p-n junction, which is a prerequisite of a connecting unit, leading to a significant performance improvement in the tandem devices.

Fullerene and Pentacene as a Pure Organic Connecting Layer in Tandem Organic Light Emitting Devices

In this paper, a white organic light-emitting device (WOLEDs) with multiple-emissive-layer structure has been fabricated. The device has a simple structure of indium tin oxide (ITO)/NPB (20 nm)//DPVBi(20 nm)/CDBP:xIr(btp)2acac(10 nm)/Alq3 (25 nm)/BCP (5 nm)/CsF (1 nm)/Al (150 nm) (x= 0.15, 2.5 and 3.0 wt%), where NPB and BCP are used as the hole-injecting layer, electron transporting and hole blocking layer, respectively. White light emission was realized in an OLED with 2.5% Ir(btp)2acac doping concentration. The device exhibits peak efficiency of 1.93 cd/A at 9 V and maximum brightness of 7005 cd/m2 at 14 V. The Commission International de I’Eclairage (CIE)(1931) coordinates of white emission are well within the white zone, which moves from (0.35,0.33) to (0.26,0.30) when the applied voltage is varied from 5 V to 14 V.

/pdf/white-organic-light-emitting-devices-based-on-multiple-5cz35dw51h.pdf

Tsung-Syun Huang

Papers

Study of organic thin film transistor with polymethylmethacrylate as a dielectric layer

Three-Band White Light-Emitting Diodes Based on Hybridization of Polyfluorene and Colloidal CdSe–ZnS Quantum Dots

Poly(methyl methacrylate) Dielectric Material Applied in Organic Thin Film Transistors

Fullerene and Pentacene as a Pure Organic Connecting Layer in Tandem Organic Light Emitting Devices

White Organic Light Emitting Devices Based on Multiple Emissive Nanolayers