Jinsong Luo

High-Work-Function Transparent Conductive Oxides with Multilayer Films

Transparent conductive oxide (TCO) films using WO3/Ag/WO3 (WAW) were fabricated under room temperature conditions. WAW has a low sheet resistance of 12 Ω/sq and a work function of 6.334 eV. This is one of the TCOs with the highest work function. These properties make it useful for application in electroluminescent devices and solar cells. Both theoretical calculation and experimental results show that the two WO3 layers strongly affect transparency, while the Ag layer determines transmittance and electrical performances. These rules can be applied in all dielectric/metal/dielectric structures.

Silver nanowire/polyimide composite transparent electrodes for reliable flexible polymer solar cells operating at high and ultra-low temperature

A high and ultra-low temperature resistant flexible polymer solar cell was produced using a silver nanowire and polyimide composite transparent electrode. The composite transparent electrode exhibited excellent opto-electrical properties and flexibility across a wide temperature range of −150 to 250 °C. It also demonstrated strong adhesion, good abrasion performance, and excellent thermal and chemical stability. The power conversion efficiency of the flexible polymer solar cell based on this film was comparable to the device based on a flexible indium tin oxide electrode, and is quite stable under a wide range of applied temperatures.

Ultrathin and efficient flexible polymer photovoltaic cells based on stable indium-free multilayer transparent electrodes

A method of fabricating ultrathin (∼25 μm-thick) and efficient flexible polymer PV cells based on an indium-free transparent electrode with the structure of SiO2/WO3/Ag/WO3 (SWAW) has been developed. The SWAW flexible electrode exhibits excellent optical and electrical properties, with a high transmittance of ∼90%, combined with a low sheet resistance of ∼9 Ω sq−1, and a work function of 5.16 eV. The flexible SWAW electrode is stable through 2000 bending cycles, has strong adhesion, and is thermally and environmentally stable. The performance of the polymer PV cells with the SWAW electrode are competitive with devices based on indium tin oxide (ITO) electrodes, which indicates that the SWAW electrode is a potential candidate for low-cost, light-weight and flexible transparent electrodes to replace ITO in efficient optoelectronic devices.

Toward highly fluorescence and ultralow-threshold amplified spontaneous emission in ordered solid state from twin-tapered bi-1,3,4-oxadiazole derivatives

We report several influential factors for achieving high fluorescent quantum yield and low ASE threshold from twin-tapered bi-1,3,4-oxadiazole derivatives by theoretical and experimental investigations. High fluorescence of BOXD-T3 in either apolar solvents or in the aggregating states were due to increased conjugation and a co-planar structure in the excited state, a four-level photophysical cycle between ground state and excited state, and co-planar formation of a rigid backbone with the tendency for slipped stacking. High fluorescence efficiency, high kr value, high σe value, polarized and self-waveguided emissions in BOXD-T3 solution processed aligned film contributed to the ultralow ASE threshold. Extremely strong fluorescence of the microbelt-like organogel BOXD-T3 with fluorescence quantum yield of near unity was achieved. This work paves the way toward obtaining highly fluorescent and ultralow-threshold ASE in an ordered solid state from bi-1,3,4-oxadiazole derivatives.

Highly efficient organic light-emitting devices beyond theoretical prediction under high current density.

We develop a simple method to improve external quantum efficiencies (EQEs) of OLEDs under a wide range of current density. An insulating inorganic ultrathin layer (LiF) was sandwiched between exciton formation layer and electron transporting layer. A maximal EQE of 5.9% in a DCM based fluorescent OLED, which far exceeds the theoretical upper limit of 3.7%, was obtained under the current density of 487 mA/cm(2) with a brightness maximum of 76740 cd/m(2). The similar electroluminescence properties were also obtained in a C545T based green OLED using this method. The overall enhancement of EQE, and the nonlinear enhancement of EQE at high current density in these devices are attributed to the effect of electrical field on excitons.

N-channel transparent organic thin-film transistors with Ag/LiF bilayer transparent source–drain electrodes fabricated by thermal evaporation

In this paper, we report the use of Ag/LiF (AL) bilayer transparent source–drain (S/D) electrodes for n-channel F16CuPc-based transparent organic thin-film transistors (OTFTs). The transparent electrodes are deposited at room temperature by thermal evaporation, with devices subsequently fabricated without damaging the active layer or breaking the vacuum. Consequently, we obtain transparent OTFTs based on AL bilayer transparent S/D electrodes with good electron mobility of 1.31 × 10−2 cm−2·V−1·s−1, a high on/off ratio of 4.2 × 106, and an average visible range transmittance of 55.6%.

Pr and F co-doped SnO2 transparent conductive films with high work function deposited by ionassisted electron beam evaporation

A transparent conductive oxide (TCO) Pr and F co-doped SnO2 (PFTO) film is prepared by ion-assisted electron beam deposition. An optimized PFTO film shows a high average visible optical transmittance of 83.6% and a minimum electrical resistivity of 3.7 × 10(-3) Ω·cm corresponding to a carrier density of 1.298 × 10(20) cm(-3) and Hall mobility of 12.99 cm(2)/V⋅s. This PFTO film shows a high work function of 5.147 eV and favorable surface morphology with an average roughness of 1.45 nm. Praseodymium fluoride is found to be an effective material to dope F into SnO2 that can simplify the fabrication process of SnO2-based TCO films.

Polymer Photovoltaic Cells Based on Ultraviolet-Ozone-Treated Vanadium-Doped Indium Oxide Anodes

Polymer photovoltaic (PV) cells based on UV-ozone(UVO)-treated indium vanadium oxide (IVO) anodes are developed. The performance of cells with UVO-treated IVO film anodes without interfacial layers was significantly improved compared with those containing untreated IVO anodes. The origin of the enhancement is investigated by atomic force microscopy and photoelectron spectroscopy measurements. The results demonstrate that UVO treatment can smooth the IVO surface, and increase the work function of IVO films due to the removal of carbon contamination and a dipole resulting from a surface rich in negatively charged oxygen. UVO-treated IVO films are potential electrode materials for polymer PV cells.

High resolution electromagnetically induced transparency spectroscopy of Rydberg 87 Rb atom in a magnetic field

We have studied the high resolution spectroscopy of Rydberg state 87Rb in a ladder-type electromagnetically induced transparency (EIT) configuration at room temperature. A highly excited Rydberg atom is nearly degenerate for its hyperfine states but this degeneracy will be broken by an applied magnetic field, resulting in a spectral splitting in a coupled basis. In our ladder-type EIT experiment, we observed the high resolution spectral splitting of Rydberg atoms in an external magnetic field with two different optical polarization combinations of σ+ − σ+ and σ+ − σ− for probe and coupling laser beams. A strict theory has been set up to explain the observed spectral line position and intensity accurately considering the Zeeman effects of three EIT-concerned states all in the coupled basis. Specially for the Rydberg state, we can transform its wavefunction back into the decoupled basis for the spectral line assignment.

Inverted structural quantum dot light-emitting diodes based on Al-doped ZnO electrode

As an indium-free transparent conducting film, Al-doped zinc oxide (AZO) was prepared by magnetron sputtering technique, exhibiting good electrical, optical and surface characteristics. UPS/XPS measurements show that AZO and zinc oxide nanoparticles (ZnO NPs) have matched energy level that can facilitate the electron injection from AZO to ZnO NPs. Inverted structural green quantum dot light-emitting diodes based on AZO cathode were fabricated, which exhibits a maximum luminance up to 178 000 cd m-2, and a maximum current efficiency of 10.1 cd A-1. Therewith, combined with the simulated space-charge-limited current (SCLC) theory, the measured current density-voltage characteristics of charge-only devices were analyzed. It demonstrated that AZO and ZnO NPs had much better electron injection efficiency than ITO, showing a electron injection efficiency close to 100%. By studying the relationship between the electric field and the current density, the measured curve of AZO-based devices nearly fits the theoretical curve of SCLC and the AZO electrode has a better ohmic contact with ZnO NPs than ITO.