nan Rusli

High efficiency planar Si/organic heterojunction hybrid solar cells

We present an efficient hybrid solar cell based on poly (3,4-ethylene-dioxythiophene):polystyrenesulfonate and planar Si with (100) and (111) orientations. The effect of Si surface native oxide on cell performance is studied. Compared to cell with hydrogen-terminated Si surface, the cell with oxygen-terminated Si surface reveals a 530-fold increase in power conversion efficiency (PCE) from 0.02% to 10.6%. The formation of SiOx-Si bonds poses a net positive surface dipole which leads to a favorable band alignment for charge separation. However, thicker oxide degrades cell performance due to higher series resistance. This study demonstrates the highest PCE reported to-date in this field.

Highly efficient Si-nanorods/organic hybrid core-sheath heterojunction solar cells

We report a hybrid solar cell based on well-aligned crystalline silicon nanorods (SiNRs) and an organic semiconductor, 2,2′,7,7′-Tetrakis-(N,N-di-4-methoxyphenylamino)-9,9′-spirobifluorene (Spiro-OMeTAD), in a core-sheath heterojunction structure. The device is formed by spin coating Spiro-OMeTAD on SiNRs array fabricated by electroless chemical etching. A silver grid on a conductive poly (3,4-ethylene-dioxythiophene): polystyrenesulfonate layer is used as the top transparent anode. A power conversion efficiency of 10.3% has been obtained for a 1-cm2 cell with 0.35-µm long SiNRs. The high efficiency and simple solution process used suggest that such devices are promising for developing low cost and high efficiency SiNRs/organic solar cells.

Fabrication of n-ZnO:Al∕p-SiC(4H) heterojunction light-emitting diodes by filtered cathodic vacuum arc technique

We report the low-temperature (∼150°C) fabrication of n-ZnO:Al∕p-SiC(4H) heterojunction light-emitting diodes by filtered cathodic vacuum arc technique. Diodelike rectifying current-voltage characteristics, with turn-on voltage of ∼3.8V and low reverse leakage current of <10−2μA, were measured at room temperature. In addition, ultraviolet emission with peak wavelength of ∼385nm and full width at half maximum of ∼20nm are observed at a forward biased voltage of ∼7.4V. The ultraviolet electroluminescence from the heterojunction is originated from the exciton-exciton scattering inside the n-ZnO:Al film.

Time-resolved photoluminescence spectra of strong visible light-emitting SiC nanocrystalline films on Si deposited by electron-cyclotron-resonance chemical-vapor deposition

SiC nanocrystalline films on Si substrates deposited using advanced electron-cyclotron-resonance chemical-vapor deposition exhibit intense visible light emission at room temperature under laser excitation. Continuous-wave and time-resolved photoluminescence measurements for these SiC films were carried out at room temperature. The photon energy of the dominant emission peaks is higher than the band gap of cubic SiC. Room-temperature optical absorption measurements show a clear blueshift of the band gap of the samples with a decrease of the average size of the nanoclusters, indicating an expected quantum-confinement effect. However, the emission spectra are basically independent of the size. Temporal evolution of the dominant emissions exhibits double-exponential decay processes. Two distinct decay times of ∼200 ps and ∼1 ns were identified, which are at least two orders of magnitude faster than that of the bound-exciton transitions in bulk 3C–SiC at low temperature. Strong light emissions and short decay ...

Y-junction carbon nanotubes grown by in situ evaporated copper catalyst

Y-junction carbon nanotubes have been grown by hot-filament chemical vapor deposition for which a gas mixture of acetone and hydrogen was fed and in situ evaporated copper was supplied. Transmission electron microscopy images reveal that, two of three branching angles around the Y-junction are obtuse (>90°) while the other is sharp (<90°). The sharp branching angles ranging between 50° and 80° are nearly twice the bending angles of simple bend junctions. This indicates that the Y-junction can be presented in structure as a combination of two bend junctions. An atomic configuration involving six heptagons on the three saddle surfaces is proposed to understand the topological structure of the observed Y-junction carbon nanotubes.

Effects of nanowire texturing on the performance of Si/organic hybrid solar cells fabricated with a 2.2 μm thin-film Si absorber

Hybrid solar cells are fabricated by spin coating poly(3,4-ethylene-dioxythiophene):polystyrenesulfonate (PEDOT:PSS) on planar Si and Si-nanowires (SiNWs) arrays prepared by electroless chemical etching. With only a 2.2 μm thick Si absorber thin film, the short-circuit current density and power conversion efficiency (PCE) of SiNWs/PEDOT cell increase from 12.5 to 13.6 mA/cm2 and from 5.4% to 5.6%, respectively, as compared to planar Si/PEDOT cell. A maximum external quantum efficiency of 56.6% is obtained for the SiNWs/PEDOT cell. The promising PCE obtained demonstrates the potential of realizing Si/PEDOT and SiNWs/PEDOT hybrid cells using low-cost Si thin films instead of bulk Si substrate.

Deposition of hydrogenated diamond-like carbon films under the impact of energetic hydrocarbon ions

In this article we studied the influence of bombardment energy of hydrocarbon ions on the properties of hydrogenated diamond-like carbon (DLC) films using x-ray reflectivity, Raman spectroscopy, and Fourier-transform infrared. The DLC films were prepared with an electron cyclotron resonance system using H2 and CH4 gases and the ion energy was tunable through a rf-induced dc bias voltage. It was observed that the surface roughness is increased and C–H bonded hydrogen concentration is decreased with increased ion energy, whereas the mass density, hardness, and sp3/sp2 ratio exhibited optimum values. A thin SiC layer was found to form between the DLC films and silicon substrates. Two proposed carbon deposition mechanisms, i.e., the shallow implantation (subplantation) model and the adsorbed layer model, are examined based on the results obtained in this study. Our results indicate that ion bombardment energy is a critical factor in determining the film properties and the ion subplantation could be an importa...

Atomic structure and defect densities in low dielectric constant carbon doped hydrogenated silicon oxide films, deposited by plasma-enhanced chemical vapor deposition

Results of structural characterization by Fourier transform infrared spectroscopy, x-ray diffraction, and specular x-ray reflectivity measurements are employed for the interpretation of electrical measurement data and the deconvoluted distribution of electron states, N(E) of carbon doped hydrogenated silicon oxide (SiOCH) low-k dielectric films. Atomic structure of the films is identified as a mixture of a dominant and totally amorphous SiO2-like phase with a partially polycrystalline SiC phase. The n-type dc conductivity that dominates in this material points to the principal role of the SiC-like phase in the dc transport of the SiOCH material. The deep level transient spectroscopy technique is applied for the N(E) shape studies in the energy range up to 0.7 eV below the conduction band bottom. Typical N(E) values lie in the 1010–1014 eV−1 cm−3 range for films deposited at different ratios of tri-methyl-silane to oxygen flow rate. No correlation between the N(E) shape and the film deposition conditions h...

Hydrogenated nanocrystalline silicon carbide films synthesized by ECR-CVD and its intense visible photoluminescence at room temperature

Hydrogenated nanocrystalline silicon carbide (nc-SiC:H) films, which contain nanosize SiC crystals embedded in a-SiC:H matrix were fabricated by the electron cyclotron resonance chemical vapor deposition (ECR-CVD) technique. It was found that under the deposition conditions of strong hydrogen dilutions and high microwave power, films containing SiC nanocrystallites embedded in an SiC:H amorphous matrix could be obtained, as shown by the use of high resolution transmission electron microscopy. Infrared absorption, Raman scattering and X-ray photoelectron spectroscopy studies have also confirmed the successful fabrication of these nc-SiC:H films. Very strong photoluminescence in the visible range with a peak energy of 2.64 eV could be observed from these films at room temperature. Temporal evolution of the PL at the peak emission energy exhibits a bi-exponential decay process with lifetimes that are in the order of ps and ns. The strong light emission and short PL lifetimes observed strongly suggest that the radiative recombination is a result of direct optical transitions in the SiC nanocrystallites. The results obtained in this study show that these nc-SiC:H films are potentially suitable as active layers in large area flat panel displays.

Hydrogenated amorphous silicon carbide deposition using electron cyclotron resonance chemical vapor deposition under high microwave power and strong hydrogen dilution

We have investigated the growth of a-Si1−xCx:H using the electron cyclotron resonance chemical vapor deposition (ECR-CVD) technique, under the conditions of high microwave power and strong hydrogen (H2) dilution. The microwave power used is 900 W and a gas mixture of CH4 and SiH4 diluted in H2 is varied to give carbon (C) fractions x ranging from 0 to 1. We aim to understand the effects of these deposition conditions on the characteristics of ECR-CVD grown a-Si1−xCx:H films at different x. Their microstructure and optical properties are investigated using infrared absorption, Raman scattering, UV-visible spectrophotometry, and photothermal deflection spectroscopy. Information on the atomic fraction x is obtained with Rutherford backscattering spectrometry. The B parameter in the Tauc relation is found to decrease and the Urbach energy Eu increase with x, which are indicative of a higher degree of disorder with C incorporation. At intermediate x, the presence of Si–C bonds can be clearly seen from the IR a...