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In this study, we synthesized ZnO nanowires using Au catalytic particles formed on a ZnO seed layer. We modulated the microstructure of the ZnO seed layer by changing the sputtering power to investigate how the underlying ZnO film microstructure affects the distribution of ZnO nanowires. Examining the samples after each of the three key steps of the growth process (ZnO seed layer deposition, Au catalytic particle formation, and nanowire growth) using various characterization methods such as scanning electron microscopy, transmission electron microscopy, and x-ray diffraction helped us illuminate the profound impacts of the grain size of the seed layer on the nanowire density.
This study examined the performance of poly(3-hexylthiophene-2,5-diyl)(P3HT)- and [6,6]-phenyl C61 butyric acid methyl ester (PCBM)-based organic solar cells (OSCs) with a pyromellitic dianhydride (PMDA) cathode interfacial layer between the active layer and cathode. The effect of inserting the cathode interfacial layer with different thicknesses was investigated. For the OSC samples with a 0.5 nm thick PMDA layer, the power conversion efficiency (PCE) was approximately 2.77% under 100 mW/cm2 (AM1.5) simulated illumination. It was suggested that the PMDA cathode interfacial layer acts as an exciton blocking layer, leading to an enhancement of the OSC performance.
The road to achieve ultra high efficiency is through multi-junction solar cells operating at high solar concentrations, larger than 1000 suns. Critical to the success of this approach is the development of tunnel junctions (TJ) that serve as electrically low loss interconnections, yet are optically transparent, using high band gap semiconductor material systems. We have previously reported the fabrication of a TJ made of n+-InGaP/ p+-AlGaAs with a band gap about 1.9 eV using Se and C doping, respectively. This TJ structure has a peak current density of 88 A/cm2 allowing it to be implemented in a three junction cell structure at solar concentrations as high as 4000 suns (x4000). Almost all reported conversion efficiencies higher than 40% have used this tunnel junction. This very high peak current density is unexpected in a high band gap material system, which is good news for the multi junction solar community. This seems to be due to the fact that the InGaP/AlGaAs interface has a staggered band line up. We will present the effect of this band line up at the heterointerface and its effect on the width of the depletion region and the peak current density. We also compare the current result from this heterostructure junction with an artificial homojunction made of n+-AlGaAs/ p+-AlGaAs doped to the same levels as that of the heterojunction. Results from the homojunction showed that peak current density is about one half of that obtained from the heterojunction at the same doping levels. A reasonable match between experimental result and the model was obtained when a value of 150 meV was used for ΔEc, the conduction band discontinuity at the interface. Both experiment and theory predicted that at a current density of about 80 A/cm2 with only about a few tens of meV drop across the TJ. This will have a minimal effect on the overall efficiency of the tandem solar cell structure when used at high solar concentrations.
Rapid thermal annealing (RTA) processing under N2 and O2 ambient is suggested and characterized in this work for improvement of SiCOH ultra-low-k (k = 2.4) film properties. Low-k film was deposited by plasma-enhanced chemical vapor deposition (PECVD) with decamethylcyclopentasiloxane and cyclohexane precursors. The PECVD films were treated by RTA processing in N2 and O2 environments at 550 °C for 5 min, and k values of 1.85 and 2.15 were achieved in N2 and O2 environments, respectively. Changes in the k value were correlated with the chemical composition of C–Hx and Si–O related groups determined from the Fourier transform infrared (FTIR) analysis. As the treatment temperature was increased from 300 to 550 °C, the signal intensities of both the CHx and Si–CH3 peaks were markedly decreased. The hardness and modulus of the film processed by RTA have been determined as 0.44 and 3.95 GPa, respectively. Hardness and modulus of RTA-treated films were correlated with D-group [O2Si–(CH3)2] and T-group [O3Si–(CH3)] fractions determined from the FTIR Si–CH3 bending peak. The hardness and modulus improvement in this work is attributed to the increase of oxygen content in (O)x–Si–(CH3)y by rearrangement.
We investigated effects of postdeposition heat treatment (HT) on the properties of plasma polymer films deposited by plasma-enhanced chemical vapor deposition using a mixture of decahydronaphthalene and tetraethyl orthosilicate as the precursors, which were referred to as plasma-polymerized decahydronaphthalene:tetraethyl orthosilicate (PPDHN:TEOS) films. HTs at 350, 450, and 500 °C decreased the relative dielectric constant k of the PPDHN:TEOS films from 3.16, the k value of the as-deposited film, to 2.82, 2.72, and 3.02, respectively. The change of k value as a function of HT temperature was correlated with the change of Fourier transform infrared absorption peaks of O–H, C = O, and Si-related groups. As the HT temperature increased, the thermal stability of the PPDHN:TEOS film increased. PPDHN:TEOS films, as-deposited or heat treated, showed leakage current density in the order of 10−7 A/cm2 at 1 MV/cm.
Effects of an Al2O3 nanothin film between the emitting layer and the sputterdeposited cathode were studied for organic light-emitting diodes (OLEDs) with indium–tin–oxide, NN′-dephenyl-NN′-bis)(3-methylphenyl)-1,1′-diphenyl-4,4′-diamine, tris(8-hydroxyquinoline)aluminum (Alq3), and aluminum (Al) as an anode, a hole transport layer, an emitting layer (EML), and a cathode, respectively. The performance of the OLEDs with sputter-deposited Al cathodes was inferior to that of the OLED with the evaporated Al cathode. However, the insertion of an Al2O3 nanothin film with a proper thickness between the EML and the sputter-deposited Al cathode was effective to alleviate performance degradation of the OLEDs with sputter-deposited Al cathodes in current flow and light emission. It is considered that both protection of EML by Al2O3 from the sputtering damage and higher luminance by the presence of a thin insulating layer between the EML and the cathode alleviated performance degradation of the OLED with an Al2O3 cathode buffer layer. The Al2O3 buffer layer could not alleviate quantum efficiency reduction caused by the sputtering damage.
Effects of plasma power on the properties of polymerlike organic thin films deposited by plasma-enhanced chemical vapor deposition using the toluene precursor were studied. As the plasma power was increased from 5 to 60 W, the relative dielectric constant increased from 2.53 to 2.85. The film deposited at higher plasma power showed higher thermal stability. The film deposited at 60 W was stable up to 400 °C. All the films were insulating under applied field ≤1 MV/cm.
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