Yajie Yang

Interface engineering of high efficiency perovskite solar cells based on ZnO nanorods using atomic layer deposition

Despite the considerably improved efficiency of inorganic–organic metal hybrid perovskite solar cells (PSCs), electron transport is still a challenging issue. In this paper, we report the use of ZnO nanorods prepared by hydrothermal self-assembly as the electron transport layer in perovskite solar cells. The efficiency of the perovskite solar cells is significantly enhanced by passivating the interfacial defects via atomic layer deposition of Al2O3 monolayers on the ZnO nanorods. By employing the Al2O3 monolayers, the average power conversion efficiency of methylammonium lead iodide PSCs was increased from 10.33% to 15.06%, and the highest efficiency obtained was 16.08%. We suggest that the passivation of defects using the atomic layer deposition of monolayers might provide a new pathway for the improvement of all types of PSCs..

Polarization induced hole doping in graded AlxGa1−xN (x = 0.7 ∼ 1) layer grown by molecular beam epitaxy

Polarization induced hole doping on the order of ∼1018 cm−3 is achieved in linearly graded AlxGa1−xN (x = 0.7 ∼ 1) layer grown by molecular beam epitaxy. Graded AlxGa1−xN and conventional Al0.7Ga0.3N layers grown on AlN are beryllium (Be) doped via epitaxial growth. The hole concentration in graded AlxGa1−xN:Be (x = 0.7 ∼ 1) layers demonstrates that polarization generates hole charges from Be dopant. The Al0.7Ga0.3N layer is not conductive owing to the absence of carriers generated from the Be dopant without the inducement of polarization. Polarization doping provides an approach to high efficiency p-type doping in high Al composition AlGaN.

Porous conducting polymer and reduced graphene oxide nanocomposites for room temperature gas detection

We report the chemical in situ deposition of a porous conducting polymer poly(3,4-ethylenedioxythiophene) (PEDOT) on reduced graphene oxide (RGO) film as an efficient chemiresistor sensor platform for room temperature NH3 gas detection. A good covering of porous PEDOT on RGO was achieved through a simple baking treatment during the in situ polymerization of PEDOT. The good covering of porous PEDOT on the RGO surface was confirmed by SEM, UV-Vis spectra, and FT-IR spectra methods. The gas sensing performance revealed that, in contrast to bare RGO and common PEDOT, the porous PEDOT/RGO based gas sensor exhibited an obvious sensitivity enhancement as well as response/recovery performance. The large surface area and very open structure of the porous PEDOT resulted in an excellent synergistic effect between PEDOT and RGO during the gas sensing process. As a result of the uniform distribution of the PEDOT porous network on the RGO sheets, this nanocomposite based sensor also exhibited higher selectivity to NH3 in contrast to other reductive analyte gases.

Ordered and ultrathin reduced graphene oxide LB films as hole injection layers for organic light-emitting diode

In this paper, we demonstrated the utilization of reduced graphene oxide (RGO) Langmuir-Blodgett (LB) films as high performance hole injection layer in organic light-emitting diode (OLED). By using LB technique, the well-ordered and thickness-controlled RGO sheets are incorporated between the organic active layer and the transparent conducting indium tin oxide (ITO), leading to an increase of recombination between electrons and holes. Due to the dramatic increase of hole carrier injection efficiency in RGO LB layer, the device luminance performance is greatly enhanced comparable to devices fabricated with spin-coating RGO and a commercial conducting polymer PEDOT:PSS as the hole transport layer. Furthermore, our results indicate that RGO LB films could be an excellent alternative to commercial PEDOT:PSS as the effective hole transport and electron blocking layer in light-emitting diode devices.

Vapor Phase Polymerization Deposition Conducting Polymer Nanocomposites on Porous Dielectric Surface as High Performance Electrode Materials

We report chemical vapor phase polymerization (VPP) deposition of poly(3,4-ethylenedioxythiophene) (PEDOT) and PEDOT/graphene on porous dielectric tantalum pentoxide (Ta2O5) surface as cathode films for solid tantalum electrolyte capacitors. The modified oxidant/oxidant-graphene films were first deposited on Ta2O5 by dip-coating, and VPP process was subsequently utilized to transfer oxidant/oxidant-graphene into PEDOT/PEDOT-graphene films. The SEM images showed PEDOT/PEDOT-graphene films was successfully constructed on porous Ta2O5 surface through VPP deposition, and a solid tantalum electrolyte capacitor with conducting polymer-graphene nano-composites as cathode films was constructed. The high conductivity nature of PEDOT-graphene leads to resistance decrease of cathode films and lower contact resistance between PEDOT/graphene and carbon paste. This nano-composite cathode films based capacitor showed ultralow equivalent series resistance (ESR) ca. 12Ω and exhibited excellent capacitance-frequency performance, which can keep 82% of initial capacitance at 500 KHz. The investigation on leakage current revealed that the device encapsulation process has no influence on capacitor leakage current, indicating the excellent mechanical strength of PEDOT/PEDOT-gaphene films. This high conductivity and mechanical strength of graphene-based polymer films shows promising future for electrode materials such as capacitors, organic solar cells and electrochemical energy storage devices.

Detection of Volatile Organic Compounds Using Langmuir-Blodgett Films of Zinc-Porphyrin and Zinc-Phthalocyanine

Detection of volatile organic compounds (VOCs) by electronic optical nose based on sensing thin films is becoming more interesting in modern industry and daily life. The thin films of zinc-porphyrin and zinc-phthalocyanine fabricated by Langmuir-Blodgett (LB) technique onto quartz substrates have been used as sensing elements for electronic optical nose application. Absorption spectra range of the both organic elements in a chloroform solution and the LB solid state thin films were acquired by using a UV-1700 spectrometer. As an electronic gas sensing test, the optical absorbance performance after the exposure of LB films to different VOCs, and dry air was investigated. The results indicated that the ZnTPP and ZnPc LB films showed different gas sensitivity due to different molecule structure. Besides, a 2 × 1 colorimetric array is fabricated by immobilizing sensing thin film on a silica substrate, and the vapor molecules of pyridine and methanol can be easily detected.

Influence of molecular weight on the dielectric and energy storage properties of poly(vinylidene fluoride)

The molecular weight shows great influence on dielectric and energy storage performance of poly(vinylidene fluoride) (PVDF) films and related devices. In this letter, the influences of molecular weight on the dielectric and energy storage properties of PVDF films were studied. It has been found that, under a 1000 kV/cm electric field, the low-molecular-weight PVDF film presents a much higher energy storage efficiency as high as 80.10%, nearly three times as much as the high-molecular-weight PVDF film. Moreover, the low-molecular-weight PVDF film also shows high resistivity, representing an order of magnitude improvement over the high-molecular-weight PVDF film, which is more desirable and promising for high performance pulse discharge capacitor application.

Self-assembly of conducting polymer nanowires as hole injection layer for organic light-emitting diodes applications

We reported a controlled architecture growth of high density and ordered nanowire film of poly(3,4-ethylene dioxythiophene) (PEDOT) via Langmuir-Blodgett (LB) technique, and self-assembly performance of PEDOT nanowires at air/water interface was investigated in detail. The conducting film consisting of high density and ordered nanowires was transferred onto ITO substrate as a hole injection layer for organic light emitting diodes (OLEDs). The results showed that, compared to conventional PEDOT film, the improved performance of OLEDs was obtained after using ordered PEDOT nanowire layer as hole injection layer. It also indicated that compact arrangement and well-ordered structure of conducting channel was attributed to the improvement of OLED performance, leading to the increase of charged carrier mobility in hole injection layer and the recombination rate of electrons and holes in the electroluminescent layer.

Surface modified polysiloxane a sensitive coatings for QCM sensors

A quartz crystal microbalance (QCM) gas sensor with polysiloxane sensing film was fabricated for detection of dimethyl methyl phosphonate (DMMP), the simulant of chemical warfare agents (CWAs). Poly(methyl-3,3,3-trifluoropropylsiloxane) (PMTFPS) was oxygen plasma treated and then grafted with sulfosalicylic acid (SSA). The resultant SSA modified PMTFPS (SMP) was drop-coated on the electrode of QCM. Compared with the PMTFPS-QCM and SSA-QCM sensors, the sensitivity of SMP-QCM sensor was much higher. However, the SMP films showed less resistance to humidity variations. The selectivity of SMP-QCM sensor to DMMP was also investigated, and better results was showed out after SSA grafted.

Polarization induced hole doping in graded AlxGa1-xN (x=0.7 similar to 1) layer grown by molecular beam epitaxy

Polarization induced hole doping on the order of ∼1018 cm−3 is achieved in linearly graded AlxGa1−xN (x = 0.7 ∼ 1) layer grown by molecular beam epitaxy. Graded AlxGa1−xN and conventional Al0.7Ga0.3N layers grown on AlN are beryllium (Be) doped via epitaxial growth. The hole concentration in graded AlxGa1−xN:Be (x = 0.7 ∼ 1) layers demonstrates that polarization generates hole charges from Be dopant. The Al0.7Ga0.3N layer is not conductive owing to the absence of carriers generated from the Be dopant without the inducement of polarization. Polarization doping provides an approach to high efficiency p-type doping in high Al composition AlGaN.