Yu-Fan Chang

Continuous blade coating for multi-layer large-area organic light-emitting diode and solar cell

A continuous roll-to-roll compatible blade-coating method for multi-layers of general organic semiconductors is developed. Dissolution of the underlying film during coating is prevented by simultaneously applying heating from the bottom and gentle hot wind from the top. The solvent is immediately expelled and reflow inhibited. This method succeeds for polymers and small molecules. Uniformity is within 10% for 5 cm by 5 cm area with a mean value of tens of nanometers for both organic light-emitting diode (OLED) and solar cell structure with little material waste. For phosphorescent OLED 25 cd/A is achieved for green, 15 cd/A for orange, and 8 cd/A for blue. For fluorescent OLED 4.3 cd/A is achieved for blue, 9 cd/A for orange, and 6.9 cd/A for white. For OLED with 2 cm by 3 cm active area, the luminance variation is within 10%. Power conversion efficiency of 4.1% is achieved for polymer solar cell, similar to spin coating using the same materials. Very-low-cost and high-throughput fabrication of efficient ...

Formation and structure of epitaxial ruthenium silicides on (111)Si

Epitaxial ruthenium silicides have been successfully grown on silicon for the first time. Chemical electroless plating of a Ru thin film on silicon with subsequent annealing is a new approach and also the first demonstration of epitaxial growth of these silicides. Transmission electron microscopy was applied to characterize phases of silicides, microstructure, and orientation relationships. Three different epitaxial phases were found and identified to be Ru2Si3, RuSi, and Ru2Si. RuSi and Ru2Si are two new phases discovered in comparison with those previously reported in thin film reactions. Furthermore, Ru2Si3 was found to be a stable phase at elevated temperatures since it can be transformed from Ru2Si and RuSi by sufficiently long annealing. Various diffraction patterns were analyzed and orientation relationships were determined. Moire’s fringes of RuSi and interfacial dislocations of Ru2Si3 and Ru2Si were found. The average spacings were measured to be from 1000 to 4000 A for Ru2Si3/Si. The composition...

Microstructure evolution of newly developed electroless ruthenium deposition on silicon observed by scanning transmission electron microscope

Autocatalytic Ruthenium thin films have been successfully deposited on silicon. The deposition reactions were proven to be electroless by the measurement of the electrochemical rest potentials of anodic and cathodic partial reactions and mixed potentials. A new method for direct observation of microstructure and formation at the initial stage of deposition has also been developed. The progressive formation and microstructure of ruthenium thin films during various growth stages have been investigated by scanning transmission electron microscopy. Deposition takes place immediately after the n‐type silicon is immersed in the electroless plating solution. The film was identified to be amorphous by the selected area electron diffraction analysis. Cross‐sectional transmission electron microscopy method was utilized to explore the uniformity and morphology of the film as well as the Ru/Si interface. Accordingly, the deposition rate was also measured with a high precision nanometer. The microstructure evolution a...

Interface and thickness tuning for blade coated small-molecule organic light-emitting diodes with high power efficiency

We developed a general method based on fluorescence microscopy to characterize the interface dissolution in multi-layer organic light-emitting diodes (OLEDs) by blade coating. A sharp bi-layer edge was created before blade coating, with the bottom layer being insoluble and top layer soluble. After blade coating, fluorescence images showed that the edge of the top layer shifted when the layer dissolved completely, whereas the bottom layers edge remained in place as a positioning mark. The dissolution depth was determined to be 15–20 nm when the emissive-layer host of 2,6-bis (3-(9H-carbazol-9-yl)phenyl) pyridine (26DCzPPy) was coated on the hole-transport layer of N,N′-bis(naphthalen-1-yl)-N,N′-bis(phenyl)-benzidine(NPB), which was consistent with a sudden drop in efficiency of orange OLEDs with layer thickness below 20 nm. Thus, the layer thickness of OLEDs was optimized to stay more than 20 nm for blade coating. For a two-color white OLED with the structure TCTA/26DCzPPy:PO-01-TB:FIrpic/TPBI, efficiency was 24 cd/A and 8.5 lm/W at 1000 cd/m2. For a three-color white OLED with Os(fptz)2(dhpm) added as the emitter, the efficiency was 12.3 cd/A and 3.7 lm/W at 1000 cd/m2. For a green device with the structure TCTA/26DCzPPy:Ir(mppy)3/TPBI, the efficiency was 41.9 cd/A and 23.4 lm/W at 1000 cd/m2.

Multilayer rapid-drying blade coating for organic solar cells by low boiling point solvents

A bulk heterojunction organic solar cell with poly(3-hexylthiophene) (P3HT) as the donor and (6,6)-phenyl-C61-butyric acid methyl ester (PCBM) as the acceptor is deposited using blade coating on a hot plate at 80 °C with hot air of 70 °C applied from above. In contrast to the 30 min of conventional dichlorobenzene solvent annealing, the rapid-drying blade coating forms a dry film in 1 s. The fabrication throughput is substantially enhanced. The blade-coated film has a smoother surface roughness of 3.5 nm compared with 10.5 nm for solvent annealing; however, the desired phase separation in the 50 nm scale forms despite the rapid drying. A single layer solar cell exhibits power conversion efficiency of 4.1% with blade coating in chlorobenzene, which is the same as solvent annealing device. A multilayer device with carrier blocking layers fabricated entirely of the less toxic toluene also exhibits efficiency of 4.1%.

Solid-state epitaxy of osmium silicide on (111)Si under reducing atmosphere

Under a mixed hydrogen/argon atmosphere epitaxial osmium silicide has been successfully grown on (111)Si for the first time. A new process of electroless deposited osmium film on Si subsequent with a suitable two‐step hydrogen annealing scheme was developed for the formation of epitaxial osmium silicide. Polycrystalline silicides of Os2Si3 and OsSi2 were found in all cases of single annealing, and the grain size increased with annealing temperature. While in the developed two‐step annealing scheme single‐crystalline silicide can form; the first step annealing was found to be critical to determine epitaxy. The epitaxial silicide was identified to be OsSi2 of orthorhombic structure. The orientation relationships between epitaxial OsSi2 and Si were found to be (040)OsSi2∥(220)Si, and [102] OsSi2∥ [111] Si.

Phase formation and identification of an epitaxial Fe‐Ni alloy silicide

Epitaxial iron‐nickel alloy silicide has been successfully grown on (111) Si for the first time using a new method of chemically electroless plating of Fe‐Ni thin films on Si with subsequent annealing schemes. The deposited film was found to be amorphous by analytical scanning transmission electron microscopy. The alloy silicide phase formed during two‐step vacuum annealing and was found to have an epitaxial relationship with the substrate Si. The composition of the eptaxial alloy silicide was identified by an energy dispersive analysis for x rays in the electron microscope. A small amount of nickel was found in the alloy silicide. The crystal structure of the silicide phase was analyzed to be that of an orthorhombic phase of FeSi2. The orientation relationships of the silicide phase with respect to the substrate were identified to be (033) (Fe,Ni)Si2∥(022) Si, (055) (Fe,Ni)Si2∥(422) Si, and [100] (Fe,Ni)Si2∥[111] Si. Typical arrays of regular interfacial dislocations of edge type, 1000 A in spacing, w...

Rear interface engineering of hybrid organic-silicon nanowire solar cells via blade coating.

In this work, we investigate blade-coated organic interlayers at the rear surface of hybrid organic-silicon photovoltaics based on two small molecules: Tris(8-hydroxyquinolinato) aluminium (Alq(3)) and 1,3-bis(2-(4-tert-butylphenyl)-1,3,4-oxadiazol-5-yl) benzene (OXD-7). In particular, soluble Alq(3) resulting in a uniform thin film with a root-mean-square roughness < 0.2nm is demonstrated for the first time. Both devices with the Alq(3) and OXD-7 interlayers show notable enhancement in the open-circuit voltage and fill-factor, leading to a net efficiency increase by over 2% from the reference, up to 11.8% and 12.5% respectively. The capacitance-voltage characteristics confirm the role of the small-molecule interlayers resembling a thin interfacial oxide layer for the Al-Si Schottky barrier to enhance the built-in potential and facilitate charge transport. Moreover, the Alq(3) interlayer in optimized devices exhibits isolated phases with a large surface roughness, in contrast to the OXD-7 which forms a continuous uniform thin film. The distinct morphological differences between the two interlayers further suggest different enhancement mechanisms and hence offer versatile functionalities to the advent of hybrid organic-silicon photovoltaics.

Spectrally resolved spontaneous emission patterns of oxide-confined vertical-cavity surface-emitting lasers

Spectrally resolved spontaneous emission patterns of oxide-confined vertical-cavity surface-emitting lasers under the subthreshold condition were investigated. The spontaneous emission mode patterns show clear and stable Hermite–Gaussian modes and high-order Laguerre–Gaussian modes associated with a distinct spectrum. The coexistence of two sets of identical low-order Hermite–Gaussian modes with different spot sizes reveals the presence of two cavity configurations. The data on mode evolution and spot size variation reveal that the modes with larger spots are supported by the cavity with the carrier-induced aperture, and become the dominant modes above the laser threshold; the modes associated with smaller spots are considered to have been formed by the cavity with the oxidized aperture and are suppressed above the threshold.

Formation and properties of copper film on Tl-(Pb, Bi)-Sr-Ca-Cu-O superconductor by electrodeposition from aqueous solution

A new process of electrodeposition in saturated cupric sulphate aqueous solution was successfully developed for the formation of copper film on a high-Tc, three Cu-O layered Tl-(Bi, Pb)-Sr-Ca-Cu-O superconductor substrate surface for the first time. Scanning electron microscopy and electron micro-probe analysis were used to investigate the morphology of the substrate surface and the composition of the copper superconductor interface. After the electrodeposition process, no evident changes in the temperature dependence of electrical resistivity were found by four-point probe measurement. The difference of magnetic properties before and after electrodeposition was investigated from magnetization measurements. Almost no degradation of the bulk properties was observed from the susceptibility data. The copper-superconductor contact was confirmed to show Ohmic behaviour by two-pointI–V characterization at liquid nitrogen boiling temperature.