Liu Xingyuan

Tricolor microcavity OLEDs based on P-nc-Si:H films as the complex anodes

A P + -nc-Si:H film (boron-doped nc-Si:H thin film) was used as a complex anode of an OLED. As an ideal candidate for the composite anode, the P + -nc-Si:H thin film has a good conductivity with a high work function (∼ 5.7 eV) and outstanding optical properties of high reflectivity, transmission, and a very low absorption. As a result, the combination of the relatively high reflectivity of a P + -nc-Si:H film/ITO complex anode with the very high reflectivity of an Al cathode could form a micro-cavity structure with a certain Q to improve the efficiency of the OLED fabricated on it. An RGB pixel generated by microcavity OLEDs is beneficial for both the reduction of the light loss and the improvement of the color purity and the efficiency. The small molecule Alq would be useful for the emitting light layer (EML) of the MOLED, and the P + -nc-Si film would be used as a complex anode of the MOLED, whose configuration can be constructed as Glass/LTO/P + -nc-Si:H/ITO/MoO3/NPB/Alq/LiF/Al. By adjusting the thickness of the organic layer NPB/Alq, the optical length of the microcavity and the REB colors of the device can be obtained. The peak wavelengths of an OLED are located at 486, 550, and 608 nm, respectively. The CIE coordinates are (0.21, 0.45), (0.33, 0.63), and (0.54, 0.54), and the full widths at half maximum (FWHM) are 35, 32, and 39 nm for red, green, and blue, respectively.

Effect of emitter position on emission intensity in an organic planar microcavity

We have fabricated a λ/2-length planar microcavity between two silver mirrors that had the same thickness and consisted of a sandwich structure LiF1/Alq3/LiF2. By altering the relative thickness of the two LiF layers, the adjustment of the position of thin layer Alq3 in the microcavity was achieved and the apparent photoluminescence (PL) intensity change was observed. The maximal emission intensity device, corresponding to the luminescence layer located at antinode, is four times that of the minimal one whose luminescence layer is near a silver mirror that is close to a node. This indicates that the coupling between vacuum electric field and dipole strongly affects the emission intensity in the forward direction of the microcavity plane. Comparing the PL intensity between the microcavity and the non-cavity devices with the same sandwich structure LiF1/Alq3/LiF2 in free space, at the resonance wavelength a maximal enhancement factor of nine is obtained.

Electrical properties of zinc-oxide-based thin-film transistors using strontium-oxide-doped semiconductors*

Strontium-zinc-oxide (SrZnO) films forming the semiconductor layers of thin-film transistors (TFTs) are deposited by using ion-assisted electron beam evaporation. Using strontium-oxide-doped semiconductors, the off-state current can be dramatically reduced by three orders of magnitude. This dramatic improvement is attributed to the incorporation of strontium, which suppresses carrier generation, thereby improving the TFT. Additionally, the presence of strontium inhibits the formation of zinc oxide (ZnO) with the hexagonal wurtzite phase and permits the formation of an unusual phase of ZnO, thus significantly changing the surface morphology of ZnO and effectively reducing the trap density of the channel.

Three-colour single-mode electroluminescence from Alq3 tuned by microcavities

Organic metal microcavities were fabricated by using full-reflectivity aluminium film and semi-transparent silver film as cavity mirrors. Unlike conventional organic microcavities, such as the typical structure of glass/DBR/ITO/organic layers/metal mirror, a microcavity with a shorter cavity length was obtained by using two metal mirrors, where DBR is the distributed Bragg reflector consisting of alternate quarter-wave layers of high and low refractive index materials. It is realized that red, green and blue single-mode electroluminescence (EL) from the microcavities with the structure, glass/Ag/TPD/Alq3/Al, are electrically-driven when the thickness of the Alq3 layer changes. Compared to a non-cavity reference sample whose EL spectrum peak is located at 520 nm with a full width at half maximum (FWHM) of 93 nm, the microcavity devices show apparent cavity effects. The EL spectra of red, green and blue microcavities are peaked at 604 nm, 540 nm and 491 nm, with FWHM of 43 nm, 38 nm and 47 nm, respectively.