Zhao Su-Ling

Phase transformation and morphology tuning of β-NaYF4:Yb3+,Er3+ nanocrystals through K+ ions codoping

In this work, a simple method to modulate the crystal phase and morphology with a large amount of K+ ions codoping is proposed. The phase changes to the mixture of β-NaYF4 and β-KYF4 with increasing the content of K+ ions to 80 mol%. When it exceeds 80 mol%, β-NaYF4 disappears gradually and β-KYF4 dominates with a poor crystalline. In addition, the morphology changes from nanosphere to nanoplate, and then to nanoprism, which indicates that a higher content of K+ ions favors the growth rates along [0001] than the [10-10] of the nanocrystals. Additionally, the upconversion (UC) luminescence properties and the ratio of red/green (R/G) UC intensity of samples with different phases and morphologies are detected, which makes it possible to tune the UC fluorescence by varying the concentration of K+ ions.

Performance improvement of MEH-PPV:PCBM solar cells using bathocuproine and bathophenanthroline as the buffer layers

In this work, bathocuproine (BCP) and bathophenanthroline (Bphen), commonly used in small-molecule organic solar cells (OSCs), are adopted as the bufier layers to improve the performance of the polymer solar cells (PSCs) based on poly(2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene) (MEH-PPV): [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) bulk heterojunction. By inserting BCP or Bphen between the active layer and the top cathode, all the performance parameters are dramatically improved. The power conversion e‐ciency is increased by about 70% and 120% with 5-nm BCP and 12-nm Bphen layers, respectively, when compared with that of the devices without any bufier layer. The performance enhancement is attributed to BCP or Bphen (i) increasing the optical fleld, and hence the absorption in the active layer, (ii) efiectively blocking the excitons generated in MEH-PPV from quenching at organic/aluminum (Al) interface due to the large band-gap of BCP or Bphen, which results in a signiflcant reduction in series resistance (Rs), and (iii) preventing damage to the active layer during the metal deposition. Compared with the traditional device using LiF as the bufier layer, the BCP-based devices show a comparable e‐ciency, while the Bphen-based devices show a much larger e‐ciency. This is due to the higher electron mobility in Bphen than that in BCP, which facilitates the electron transport and extraction through the bufier layer to the cathode.

The studies on the upconversion mechanism of ZBLAN: Er3+, Yb3+

Abstract ZBLAN glass is an interesting host for rare earth doped up-conversion materials due to a lot of advantages. In this paper, we studied the up-conversion mechanism of ZBLAN co-doped with Er 3+ and Yb 3+ ions. The energy transfer between Yb 3+ and Er 3+ was described.

Thickness dependence of surface morphology and charge carrier mobility in organic field-effect transistors

With the aim of understanding the relationships between organic small molecule field-effect transistors (FETs) and organic conjugated polymer FETs, we investigate the thickness dependence of surface morphology and charge carrier mobility in pentacene and regioregular poly (3-hexylthiophene) (RR-P3HT) field-effect transistors. On the basis of the results of surface morphologies and electrical properties, we presume that the charge carrier mobility is largely related to the morphology of the organic active layer. We observe that the change trends of the surface morphologies (average size and average roughness) of pentacene and RR-P3HT thin films are mutually opposite, as the thickness of the organic layer increases. Further, we demonstrate that the change trends of the field-effect mobilities of pentacene and RR-P3HT FETs are also opposite to each other, as the thickness of the organic layer increases within its limit.

Ca2BO3Cl:Ce3+, Tb3+: A novel tunable emitting phosphor for white light-emitting diode

Ca2BO3Cl:Ce3+, Ca2BO3Cl:Tb3+, and Ca2BO3Cl:Ce3+, Tb3+ phosphors are synthesized by a high temperature solid-state reaction. The emission intensity of Ce3+ or Tb3+ in Ca2BO3Cl is influenced by the Ce3+ or Tb3+ doping content, and the optimum concentrations of Ce3+ and Tb3+ are 0.03 mol and 0.05 mol, respectively. The concentration quenching effect of Ce3+ or Tb3+ in Ca2BO3Cl occurs, and the concentration quenching mechanism is d—d interaction for either Ce3+ or Tb3+. The Ca2BO3Cl:Ce3+, Tb3+ can produce colour emission from blue to green by properly tuning the relative ratio between Ce3+ and Tb3+, and the emission intensity of Tb3+ in Ca2BO3Cl can be enhanced by the energy transfer from Ce3+ to Tb3+. The results indicate that Ca2BO3Cl:Ce3+, Tb3+ may be a promising double emission phosphor for UV-based white light emitting diodes.

Transient demonstration of exciton behaviours in solid state cathodoluminescence under different driving voltage

In the solid state cathodoluminescence (SSCL), organic materials were excited by hot electrons accelerated in silicon oxide (SiO2) layer under alternating current (AC). In this paper exciton behaviours were analysed by using transient spectra under different driving voltages. The threshold voltages of SSCL and exciton ionization were obtained from the transient spectra. The recombination radiation occurred when the driving voltage went beyond the threshold voltage of exciton ionization. From the transient spectrum of two kinds of luminescence (exciton emission and recombination radiation), it was demonstrated that recombination radiation should benefit from the exciton ionization.

The Effect of the Oxygen Plasma Treatment for ITO and ZnO Nanorods on the Electroluminescence of ZnO Nanorod/MEH-PPV Heterostructure Devices

Series devices of ITO/ZnO/ZnO nanorods/MEH-PPV/Al have been fabricated. ITO and ZnO nanorods of some devices are treated by O2 plasma. The electroluminescence of different devices is detected under different biases. UV electroluminescence of ZnO nanorods at 380nm is observed in all the devices. The intensity of 380nm increases when both ITO and ZnO nanorods are treated. The turn-on voltage of the treated device is lower than that of the non-treated device, and the EL power is enhanced. When the thickness of MEH-PPV is sufficiently thin, only 380 nm electroluminescence, besides a weak defect emission at 760 nm, is detected. The enhancement mechanism of the electroluminescence of the treated devices is discussed.

Enhanced performance in organic photovoltaic devices with a KMnO4 solution treated indium tin oxide anode modification

The properties of poly(3-hexylthiophene):(6,6)-phenyl C61 butyric acid methyl ester (P3HT:PCBM) organic photovoltaic devices (OPVs) with an indium tin oxide (ITO) anode treated by a KMnO4 solution are investigated. The optimized KMnO4 solution has a concentration of 50 mg/L, and ITO is treated for 15 min. The modification of ITO anode results in an enhancement of the power conversion efficiency (PCE) of the device, which is responsible for the increase of the photocurrent. The performance enhancement is attributed to the work function modification of the ITO substrate through the strong oxygenation of KMnO4, and then the charge collection efficiency is improved.

Characteristics of pentacene organic thin film transistor with top gate and bottom contact

High performance pentacene organic thin film transistors (OTFT) were designed and fabricated using SiO2 deposited by electron beam evaporation as gate dielectric material. Pentacene thin films were prepared on glass substrate with S–D electrode pattern made from ITO by means of thermal evaporation through self-organized process. The threshold voltage VTH was −2.75±0.1V in 0 – −50V range, and that subthreshold slopes were 0.42±0.05V/dec. The field-effect mobility (μEF) of OTFT device increased with the increase of VDS, but the μEF of OTFT device increased and then decreased with increased VGS when VDS was kept constant. When VDS was −50V, on/off current ratio was 0.48 × 105 and subthreshold slope was 0.44V/dec. The μEF was 1.10cm2/(V-s), threshold voltage was −2.71V for the OTFT device.

Effects of Thermal Annealing on the Solvent Additive P3HT PC61BM Bulk Heterojunction Solar Cells

Effects of thermal annealing on the optical, electrical and structural properties of 3 vol% 1,8-diiodoctane added P3HT:PC61BM active layers are investigated, concerning the performance of the bulk heterojunction polymer solar cells by changing the heat temperature. The structure information of the active layer is analyzed by using the grazing incidence wide angle scattering diffraction combined with the optical microscope, light absorption, photoluminescence and the external quantum efficiency spectra. The relationship between the detail of morphology and the optical, electrical properties is investigated.