Improved Charge Injection and Transport of Light-Emitting Diodes Based on Two-Dimensional Materials

Light-emitting diodes (LEDs) are considered to be the most promising energy-saving technology for future lighting and display. Two-dimensional (2D) materials, a class of materials comprised of monolayer or few layers of atoms (or unit cells), have attracted much attention in recent years, due to their unique physical and chemical properties. Here, we summarize the recent advances on the applications of 2D materials for improving the performance of LEDs, including organic light emitting diodes (OLEDs), quantum dot light emitting diodes (QLEDs) and perovskite light emitting diodes (PeLEDs), using organic films, quantum dots and perovskite films as emission layers (EMLs), respectively. Two dimensional materials, including graphene and its derivatives and transition metal dichalcogenides (TMDs), can be employed as interlayers and dopant in composite functional layers for high-efficiency LEDs, suggesting the extensive application in LEDs. The functions of 2D materials used in LEDs include the improved work function, effective electron blocking, suppressed exciton quenching and reduced surface roughness. The potential application of 2D materials in PeLEDs is also presented and analyzed

MoOx and V2Ox as hole and electron transport layers through functionalized intercalation in normal and inverted organic optoelectronic devices

To achieve fabrication and cost competitiveness in organic optoelectronic devices that include organic solar cells (OSCs) and organic light-emitting diodes (OLEDs), it is desirable to have one type of material that can simultaneously function as both the electron and hole transport layers (ETLs and HTLs) of the organic devices in all device architectures (i.e., normal and inverted architectures). We address this issue by proposing and demonstrating Cs-intercalated metal oxides (with various Cs mole ratios) as both the ETL and HTL of an organic optoelectronic device with normal and inverted device architectures. Our results demonstrate that the new approach works well for widely used transition metal oxides of molybdenum oxide (MoOx) and vanadium oxide (V2Ox). Moreover, the Cs-intercalated metal-oxide-based ETL and HTL can be easily formed under the conditions of a room temperature, water-free and solution-based process. These conditions favor practical applications of OSCs and OLEDs. Notably, with the analyses of the Kelvin Probe System, our approach of Cs-intercalated metal oxides with a wide mole ratio range of transition metals (Mo or V)/Cs from 1∶0 to 1∶0.75 can offer significant and continuous work function tuning as large as 1.31 eV for functioning as both an ETL and HTL. Consequently, our method of intercalated metal oxides can contribute to the emerging large-scale and low-cost organic optoelectronic devices.published_or_final_versio

Nanocomposition of PEDOT:PSS with metal phthalocyanines as promising hole transport layers for organic photovoltaics

PEDOT:PSS is one of the most widely used materials as a hole selective layer in organic photovoltaics due to its easy processing and high reproducibility. Unfortunately, the material is limited when testing new donor:acceptor systems due to its intrinsic frontier energy levels which typically leads to energy losses due to inadequate energy level alignment and presence of resistive losses. In this work, PEDOT:PSS:metal phthalocyanines nanocomposite thin films are formulated and used as hole transport layer for organic solar cells (OSCs). PEDOT:PSS is formulated with H2Pc, CuPc, CoPc and ZnPc metal phthalocyanines (MPc) with nanobelt morphology which confers the compatibility with the active layer. Atomic force microscopy (AFM) and x-ray diffraction (XRD) were used to study the morphology and structure of nanocomposite films, respectively. OSCs based on PEDOT:PSS:MPc nanocomposite films were fabricated and the effect of hybrid hole transport layer with various phthalocyanines on photovoltaics properties was studied. Overall, nanocomposition of PEDOT:PSS with metal phthalocyanines improves the final power conversion efficiency of solar cells by 20% by a reduction of the resistive losses due to inadequate energy level alignment. The addition of metal phthalocyanines to PEDOT:PSS is a promising method for tailor-made hole transport materials for new donor:acceptor systems to improve their efficiencies.Funding for open access charge: CRUE-Universitat Jaume

Surface and Interface Engineering for Organic Device Applications

In the last few decades, organic materials (or carbon-based materials in a broad sense), including polymers, have received much attention for their potential applications in electronics, because they have outstanding advantages such as high processibility, mechanical flexibility, and low weight. Extensive research efforts have thus been devoted to the development and advancement of organic materials for various applications, covering a wide range from molecular design to device fabrication methods. In addition, it has been recognized that surfaces and interfaces play a crucial role in the operation and performance of the devices. For instance, various interactions at organic–metal interfaces are of great importance in organic epitaxy, and also have a strong correlation with intermolecular structures and their electronic properties. In this context, the main focus of this Special Issue was collecting scientific contributions addressing surface and interface engineering with organic materials, and related applications. The diversity of contributions presented in this Special Issue exhibits relevant progress and the potential of organic materials in a variety of applications that are not limited to the fabrication of organic devices

One-Dimensional nanostructured polymeric materials for solar cell applications

Philosophiae Doctor - PhDThis work entails the preparation of various polyanilines with different morphologies and their application in photovoltaic solar cells. Zinc oxide (ZnO) with one-dimensional and flower-like morphology was also prepared by microwave irradiation and used as electron acceptors in photovoltaics devices. The morphological, structural, spectroscopic and electrochemical characteristics of these materials were determined by scanning electron microscopy (SEM), X-Ray diffraction (XRD), Raman, Fourier-transformed infrared spectroscopy (FTIR), ultraviolet and visible spectroscopy (UV-Vis), photoluminescence(PL), thermal gravimetric analysis (TGA) and cyclic voltammetry (CV) experiments. Devices fabricated from these materials were characterized under simulated AM 1.5 at 800 mW.South Afric

A Study on Charge Selective Transport for Highly Efficient Polymer Based Optoelectronic Devices

Department of Materials Science EngineeringPolymer based optoelectronic devices including polymer light-emitting diodes (PLEDs) and polymer solar cells (PSCs) have been recently focused for display, energy source and flexible electronic applications because of their advantages such as low cost, light weight, easy solution process fabrication and mechanical flexibility. Moreover, so much effort has been made to maximize their device performance through optimization of device configuration and charge selective transport. In particular, balanced charge transport via charge selective interfacial engineering or surface modification is promising for optimized device performance. According to the device configuration, interfacial engineering can improve the minority carrier transport with well-matched energy level, passivate the charge trap sites and enhance the materials compatibility. It can also block abundant majority carrier and reduce the exciton quenching, leading to improving the recombination rate of balanced charges in PLEDs while disrupting bimolecular recombination in PSCs. Here, I present variety interfacial engineering strategies employing modified charge transport layer such as graphene oxide (GO) as a hole transport layer (HTL) in conventional PLEDs and surface modified zinc oxide (ZnO) as an electron transport layer (ETL) using ionic liquid molecules (ILMs), conjugated polyelectrolyte (CPE) and amine-based polar solvents in inverted polymer light-emitting diodes (iPLEDs) and polymer solar cells (iPSCs). A GO layer with a wide band gap blocks transport of electrons from an emissive layer to an indium tin oxide (ITO) anode while reduces the exciton quenching between the GO layer and the emissive layer. As a result, the GO layer maximizes hole-electron recombination within the emissive layer leading to improvement of device performance in PLEDs. In addition, surface modified ZnO layers with various interfacial layers such as ILMs, CPE and amine-based polar solvents remarkably enhance the devices performance by introducing spontaneously oriented interfacial dipoles between the ZnO layer and active layer in iPLEDs and iPSCs. This charge selective interfacial engineering is a promising way for organic optoelectronic devices such as organic photovoltaics (OPVs), organic light-emitting diodes (OLEDs), organic thin film transistors (OTFTs), and organic laser diodes (OLDs).ope

The effects of nano-composites in bulk heterojunction thin-film organic solar cells.

Doctoral Degree. University of KwaZulu-Natal, Pietermaritzburg.Abstract available in PDF

Oxygen, relative humidity, and interlayer related issues in organic electronics

Photoluminescence (PL)-based optical O2 sensors have applications in agricultural, medical and industrial areas. In this dissertation, All organic O2 sensors are realized by using organic light emitting diodes (OLEDs), porous O2 sensing film, and organic photo detectors (OPDs). The main idea is to create the voids in the O2 sensing film to have higher PL signal; and to modify the interfacial layer for organic photovoltaics (OPVs) to have higher sensitive photo detectors. This is a big step to have integrating small compact O2 monitoring platform. The modified porous sensing films also make it possible to have O2 and relative humidity (RH) monitored where less than 10% resolution in RH is obtained. This dual detection is important since those two parameters usually work together in the organic electronics device and food packaging. Furthermore, O2 monitoring can also be applied in the OLEDs or OPVs device, The active layer with the O2 sensitive material Pd octaethylporphyrin (PdOEP) can also be used as O2 sensing film. PL decay times of the active layer contain the information about the O2 trapping, and electroluminescence (EL) decay times of the OLEDs contain the information about the device degradation