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Online learning increases the physical distance between instructors and students and depending on the mode of delivery, it can be challenging to close this gap. To ameliorate this potential for student isolation, instructors need to communicate to students in a variety of ways, blending original online resources with synchronous interactive learning activities. During 2020, 34 lecture videos were created for a large undergraduate microbiology and immunology course offered at The University of Queensland. The teaching team applied a subset of Mayer’s multimedia learning design principles – embodiment, mixed perspectives, segmenting, signalling – to create videos featuring instructor presence, multiple presentation styles, and dynamic pacing. When compared to voice-over presentations created by automated lecture capture software, the outcomes of this design process increased student engagement in video-based learning across the 2020 and 2021 course offerings. Analysis of student perception data collected by online questionnaires and interviews revealed broad agreement with the design principles used for video-based learning. However, their value of on-screen instructor visibility, graphics, and text was variable as a result of individual preferences. Together these findings present a case study in which instructional videos were developed iteratively through the selective application of multimedia design principles and strategic adaptation of existing learning resources.

We investigate the thermoelectric effect of the self-assembled monolayers (SAMs) in semiconductors (SCs). The thermoelectric performance of the SC-SAM-SC heterostructure is largely improved due to two reasons. First, the SAMs in semiconductors act as good thermal insulators. Second, the thickness of the SAMs can be smaller than one nanometer so that electrons could easily tunnel through the SAMs. As an example, we consider the GaAs-SAM-GaAs heterostructure at room temperature. The electrical conductivity, the Seebeck coefficient, and the electronic thermal conductivity as functions of donor concentration are calculated through the Boltzmann equation and the tunneling current model. The highly improved figure of merit and Seebeck coefficient demonstrate an excellent direction for fabricating high efficiency nano-thermalelectric devices.

A well adherent copper deposit on the Mg alloy (AZ31) can be obtained with a pretreatment with galvanostatic etching then followed by copper electrodeposition in an alkaline copper-sulfate plating bath. Experimental results show that the effect of galvanostatic etching on copper electrodeposition depends strongly on potential variation during anodic etching period. Oxygen-rich Cu and Mg layers were observed in the initial stage of galvanostatic etching. However, increasing the gavanostatic etching period to the potential plateau of its anodic polarization curve, the oxygen-rich Cu and Mg layers were almost removed and an activated surface of AZ31 can be achieved, which is suitable for Cu electrodeposition in the alkaline Cu-sulfate plating bath. The above-mentioned results were evidenced from the microstructure study with scanning transmission electron microscope.

An investigation of the normoxic NIPAM gel dosimeter has been undertaken. The NIPAM gel dosimeter used in the current study was mainly composed of gelatin, NIPAM, N,N′-methylenebisacrylamide (BIS), and distilled water. This study aims to measure the change in the chemical structure of the NIPAM gel dosimeter after irradiation via the 13C-NMR, 1H-NMR, and Fourier transform Raman (FT-Raman) spectra. The 13C-NMR experimental results show that the C=C bonds of NIPAM and BIS are at 126.74 and 131.62 ppm, respectively. The intensity of the C-C bond of the NIPAM gel dosimeter increases with the absorbed dose, and the dose–intensity curve of the C–C bond is determined by y = 0.0506 + 79.9 ( 1 − e 0.16 x ) (R2=0.9997). 1H-NMR and FT-Raman can also effectively determine the positions of the C=C bonds of NIPAM and BIS, and the intensity decreases as the absorbed radiation dose increases. Hence, 13C-NMR, 1H-NMR, and FT-Raman spectrometers can effectively detect the changes in the chemical structure of the polymer gel dosimeter after irradiation and successfully determine the D50 dosage in the NIPAM gel dosimeter.

Summary We have proposed a new method for the magnetic field data depth estimation based on the normalized downward continuation method. The local wavenumber of potential field data is less sensitive to the magnetization direction and is widely used in the semi-automated interpretation. We applied the normalized downward continuation to the magnetic field local wavenumber. And different normalization factors were chose to normalize the downward continuation field. We selected the iteration downward continuation method to calculate each downward continuation height data, which yielded stable and accurate result. The method was examined on the 2D synthetic magnetic data, and the maximum values of the results can indicate the depths effectively.

A simple model for size-dependent surface tension of liquid binary alloy droplets has been established based on Bulter’s equation and our model for size-dependent surface tension of pure liquid component. As an example, the surface tension of liquid Bi–Sn alloy droplets are calculated and discussed. The results show that as the size of the liquid alloy droplets decreases, the corresponding surface tension decreases. The component with lower surface tension is enriched in the surface layer at all times while relatively more another component with higher surface tension appear in the surface region when the size decreases. The effect of decreasing size on liquid alloy surface tension is like that of increasing temperature. When size is larger than about 12 nm, the size effect is small and negligible.

A pretreatment with galvanostatic etching is recommended to obtain an adherent and uniformly covered copper deposit on pure magnesium and magnesium alloy specimens (AZ31 and AZ61) in an alkaline copper-sulfate bath. The effect of galvanostatic etching on the surfaces of Mg and Mg alloy specimens can be realized by their potential variation during galvanostatic etching, in which four distinct stages could be distinguished. Galvanostatic etching to stage III, an activated surface of Mg or Mg alloy, was obtained for electroplating a uniformly covered Cu deposit in the alkaline Cu-sulfate bath. The Cu-deposited Mg or Mg alloy was used as the substrate for further Cu and then Ni electrodeposition in acid plating baths to obtain a protective Ni/Cu coating. The proposed electroplating baths are environmentally friendly, and the electrodeposition process is easy to conduct to achieve a protective coating for Mg and Mg alloys.

An environmental-friendly Cu electrodeposition process was proposed for the Magnesium alloy (AZ 31). Experimental results show that a good bonding between Cu deposit and Mg alloy surface can be achieved with a pretreatment of galvanostatic etching and then copper electrodeposition in the alkaline copper-sulfate plating bath. Microstructures between Cu deposit and Mg alloy substrate were examined with scanning electron and energy-filtering transmission electron microscopes (SEM and EF-TEM). The Cu-deposited Mg alloy can be further electroplated in acidic Cu and Ni plating baths to acquire a protective Cu/Ni deposit.

Our research aiming to improve silicon photovoltaic materials and devices extensively utilizes hot-wire chemical vapor deposition (HWCVD). We have recently achieved 18.2% heterojunction silicon solar cells by applying HWCVD a-Si:H front and back contacts to textured p-type silicon wafers. This is the best reported p-wafer heterojunction solar cell by any technique. We have also dramatically improved the quality of HWCVD silicon epitaxy and recently achieved 11 μm of epitaxial growth at a rate of 110 nm/min.

This study investigated the effects of ultrasonic pretreatment and various treatments on the aerobic degradation of four phthalic acid esters (PAEs) such as diethyl phthalate (DEP), benzyl butyl phthalate (BBP), di-n-butyl phthalate (DBP) and di-(2-ethyl hexyl)phthalate (DEHP) in sludge. The effect on PAE degradation of treating sludge with a 20 min sonication period at a power level of 0.1 W ml(-1) was evaluated. The degradation rates of the four PAEs were DBP>BBP>DEP>DEHP. Degradation rate constants (k(1)) and half-lives (t(1/2)) for the four PAEs (50 mg kg(-1)) ranged from 0.182 to 0.379 day(-1) and 1.8 to 3.8 days, respectively. The optimal pH for PAE degradation in sludge was 7.0 at 30 degrees C. PAE degradation was enhanced by the addition of yeast extract, brij 30 or brij 35 and inhibited by the addition of hydrogen peroxide. Our results show that a combination of ultrasonic pretreatment and biodegradation can effectively remove PAE from sludge.

Temperature-dependent surface tension γlv(T) and its temperature coefficient γ′lv(T)=dγlv(T)/dT for liquid silicon and germanium (l-Si and l-Ge) are thermodynamically modeled based on an established model for surface energy of crystals. Combining the relationship among γlv(T), self-diffusion coefficient D and liquid viscosity η, temperature dependent D(T) function is also modeled. The model predictions correspond to the available experimental results. It is found that γlv(T)∝T, γ′lv(T)∝T and D(T)∝T3/2 at a certain temperature range (including T T m and T ⩾ T m where Tm is the melting temperature).

In situ monitoring of material properties during thin-film deposition provides researchers with a valuable tool for maximizing solar cell performance, while also enabling efficient exploration of deposition parameter space. This article describes how our research team has utilized in situ real-time spectroscopic ellipsometry (RTSE) to maximize our productivity in two related projects. We are using hot wire chemical vapor deposition (HWCVD) for low-temperature (90–235 °C) deposition of very thin films of amorphous hydrogenated silicon for amorphous Si∕crystal-Si heterojunction (SHJ) solar cells. We are also using HWCVD for low-temperature (200–440 °C) deposition of epitaxial films of silicon on crystal-Si substrates. We utilize RTSE as both an in situ diagnostic and a postgrowth analysis tool for SHJ solar cells and epi-Si films grown by HWCVD. Using input from RTSE analysis we have achieved a photovoltaic energy conversion efficiency of 17.1% on an Al-backed p-type float-zone c-Si wafer. Epi-Si films have...

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Silicon thin layers that are either highly textured polycrystalline, randomly oriented polycrystalline, or epitaxial have been deposited by the technique of atmospheric-pressure iodine vapor transport on silicon or non-silicon substrates. Strongly [1 1 0]-textured polycrystalline silicon films are obtained by starting with a relatively low starting substrate temperature of 700°C, to increase nucleation density, then ramping up to 900°C at the end to increase growth rate. Alternatively, if a higher constant temperature of 900°C is used, we obtain polycrystalline silicon layers with randomly oriented large grains of ∼20 μm in average size. When a still higher initial substrate temperature of 1000°C is used to eliminate condensation of silicon iodides at the interface, high-quality epitaxial silicon layers are grown on silicon substrates.

We have developed a p-type, crystalline Si-based solar cell using hot-wire chemical vapor deposition (HWCVD) n-type microcrystalline Si to form an n-p junction (emitter). The CVD process was rapid and a low substrate temperature was used. The p-type Czochralski (CZ) c-Si wafer has a thickness of 400 μm and has a thermally diffused Al back-field contact. Before forming the n-p junction, the front surface of the p-type c-Si was cleaned using a diluted HF solution to remove the native oxides. The n-type emitter was formed at 220 °C by depositing 50 A a-Si:H and then a 100 A μc-Si n-layer. The total deposition time to form the emitter was less than 1 min. The top contact of the device is a lithograph defined and isolated 1×1 cm 2 and 780 A indium tin oxides (ITO) with metal fingers on top. Our best solar cell conversion efficiency is 13.3% with V oc of 0.58 V, FF of 0.773, and J sc of 29.86 mA cm −2 under one-sun condition. Quantum efficiency (QE) measurement on this solar cell shows over 90% in the region between 540 and 780 nm, but poor response in the blue and deep red. We find that the ITO top contact that acts as an antireflection layer increases the QE in the middle region. To improve the device efficiency further, J sc needs to be increased. Better emitter and light trapping will be developed in future work. The cell shows no degradation after 1000 h of standard light soaking.

The hot-wire chemical vapor deposition (HWCVD) technique was employed to deposit μc-Si emitters and a-SiNx:H passivation/antireflection films, and to hydrogenate silicon thin layers grown by atmospheric-pressure iodine vapor transport (APIVT). Photovoltaic devices with HWCVD μc-Si emitters on APIVT epitaxial silicon exhibit greater than 8% efficiency, similar to those made with diffused junctions. On polycrystalline APIVT-Si layers, a HWCVD-deposited μc-Si emitter reduces open-circuit voltage loss caused by grain boundaries. Hot-wire hydrogenation improves Hall mobility by approximately 50%. HWCVD a-SiNx:H films improve minority-carrier lifetime significantly after thermal annealing at temperatures up to 500 °C.

Demand for large silicon wafers has driven the growth of silicon crystals from 200 to 300 mm in diameter. With the increasing silicon ingot sizes, melt volume has grown dramatically. Melt flow becomes more turbulent as melt height and volume increase. To suppress turbulent flow in a large silicon melt, a new Czochralski (CZ) growth furnace has been designed that has a shallow melt. In this new design, a crucible consists of a shallow growth compartment in the center and a deep feeding compartment around the periphery. Two compartments are connected with a narrow annular channel. A long crystal may be continuously grown by feeding silicon pellets into the dedicated feeding compartment. We use our numerical model to simulate temperature distribution and velocity field in a conventional 200-mm CZ crystal growth system and also in the new shallow crucible CZ system. By comparison, advantages and disadvantages of the proposed system are observed, operating conditions are determined, and the new system is improved.

Cranial reconstruction has evolved to achieve both functional coverage and esthetic appearance. Hair preservation/reconstruction and free flaps have markedly improved the soft tissue esthetic outcome. Restoration of bony contour has been facilitated by advanced craniofacial techniques and three-dimensional alloplast.

Individualizing each patient in deciding on flap selection, flap design, hair sparing or shaving, and method of closure ensures proper treatment outcome with the goal of achieving a good cosmetic result.

The float-zone (FZ) method for silicon crystal growth produces very high purities and low defect levels because no crucibles or other heated components are used, and the melt is only in contact with solid silicon. FZ growth is thus a useful tool for the study of defect and impurity effects on material properties such as minority charge carrier lifetime τ or photovoltaic efficiency η using controlled samples in which specific defects or impurities are deliberately introduced into the high-purity, low-defect baseline material, as desired. We have used this tool for defect studies on grain size, dislocations, silicon self interstitial clusters, and fast-cooling defects, as well as for impurity studies on H, N, Fe, p-type dopants, and interactions between Fe and Ga. Float zoning was conducted in vacuum or pure argon using induction heating at 2 MHz. The ASTM F28-91 photoconductive decay method was used to measure τ after growth. Arrays of isolated diagnostic solar cell devices were used to characterize defect and impurity effects on photovoltaic parameters.

BACKGROUND: A novel transfusion-transmissible human DNA virus, TT virus (TTV), has been discovered recently. An attempt was made to determine the incidence and clinical outcome of TTV infection in recipients of blood transfusion. STUDY DESIGN AND METHODS: Serial serum samples collected as part of a prospective study of posttransfusion hepatitis were examined for TTV DNA by a nested PCR assay. RESULTS: Among 150 adults undergoing cardiac surgery, posttransfusion specimens from 59 individuals were positive for TTV DNA. Pretransfusion sera were found to be positive in 13 of these individuals. Therefore, 46 (33.6%) of the 137 previously uninfected patients developed new TTV viremia after transfusion. Among the 46 patients, 3 were coinfected with HCV, 5 were coinfected with HGV, and 38 were infected with TTV alone. No apparent symptoms or signs were noted in the 38 patients infected by TTV alone or the 5 infected with HGV plus TTV. The average peak serum ALT activity was 31 IU per L, with persistently normal levels in 34 of the 38 patients with TTV infection alone. In 8 other patients who subsequently developed well-documented non-A-G hepatitis, 3 were positive for TTV (3/8 vs. 46/137, p = 0.8). In 12 patients followed for more than 1 year, TTV viremia persisted in every case. CONCLUSION: In this population, TTV is transmitted by transfusion to approximately 30 percent of patients who undergo cardiac surgery. Most of the infections appear to become persistent. Despite the high prevalence rate, TTV does not appear to cause hepatitis on its own.

A quantitative theory for modeling the laser-generated transient ultrasonic Lamb waves, which propagates along arbitrary directions in orthotropic plates, is presented by employing an expansion method of generalized Lamb wave modes. The displacement field is expressed by a summation of the symmetric and antisymmetric modes in the surface stress-free orthotropic plate, and therefore the theory is particularly appropriate for waveform analyses of Lamb waves in thin plates because one needs only to evaluate several lower modes. The transient waveforms excited by the thermoelastic expansion and the oil-coating evaporation are analyzed for a transversely isotropic thin plate. The results show that the theory provides a quantitative analysis to characterize anisotropic elastic stiffness properties of orthotropic plates by laser-generated Lamb wave detection.

Based on our model for size-dependent cohesive energy, the size-dependent evaporation temperature of nanocrystals has been modeled without any adjustable parameter. The model predicts a decrease of the evaporation temperature of nanocrystals with decreasing size. The model predictions are in good agreement with available experimental results for Ag, Au and PbS nanocrystals.

Al segregation at the solid-liquid interface and Cu segregation at the free silicon surface were studied in liquid-phase epitaxy (LPE) of silicon thin layers from mixtures of Cu-Al-Si. Using the multi-component regular solution model and experimental results, we found that Si-Al and Si-Cu interactions in the liquid solution are repulsive, and Al-Cu interaction is attractive. As a result, Al doping in silicon epitaxial layers is controlled by both Cu and Al compositions in the growth solution to allow epitaxy at about 900°C, with a substantial amount of Al present in the liquid for substrate surface-oxide removal. On the other hand, Cu concentration in the grown layers is determined by both the solid-liquid interface segregation during growth and segregation at the silicon surface after growth. The surface segregation phenomenon can be used to getter Cu from the bulk of silicon layers so that its concentration is much lower than its solubility at the layer growth temperature and the reported 10 17 cm -3 degradation onset for solar-cell performance.

In pursuit of device-quality layer formation on cast, metallurgical-grade silicon (MG Si) substrates for solar cells, the growth kinetics of silicon liquid phase epitaxy (LPE) from metal solutions was studied. We found an ideal solvent system, Cu Al, for growth of Si layers with thicknesses of tens of microns on cast MG Si substrates by LPE at temperatures near 900°C. This solvent system utilizes Al to ensure good wetting between the solution and substrate by removing silicon native oxides, and employs Cu to control Al doping into the layers. Isotropic growth is achieved because of a high concentration of solute silicon in the solution and the resulting microscopically rough interface. As a result, macroscopically smooth Si layers have been grown on cast MG Si that are suitable for device fabrication. With the microscopically rough interface, the growth rate has been studied with a diffusional model involving a boundary layer that takes the melt convection into account. The model was found to be in good agreement with experimental results, indicating only a small boundary layer (∼ 0.1 cm) and a silicon diffusivity of ∼ 2 × 10−4 cm2 s−1 in the liquid. The thin layer (∼ 30 μm) grown on the MG-Si substrate has a minority-carrier diffusion length greater than the layer thickness.

Because of the current interest in thin-layer (5–50 μm) crystalline silicon for photovoltaic (PV) applications, we have grown Si layers on (111) single crystal Si substrates from the metal solvents Ga, Sn, and Cu with a particular emphasis on Cu. A substrate dipping technique was used, and the growth temperature was typically near 950°C. The conditions of growth, morphology, qualitative solvent incorporation characteristics, and electrical properties of the solution-grown layers are presented and discussed. Thin single crystal layers with suitable impurity characteristics for photovoltaic use were obtained, and solar cells with 15% conversion efficiency were fabricated on 5 μm thick layers grown on single crystal Si substrates. This is 97% of the efficiency obtained on substrates without a grown layer, and indicates that the Cu solution growth process does not significantly degrade cell performance.

Swirl defects (A- or B-type) and frozen-in defects are found to be carrier recombination centers in dislocation-free, as-grown, float-zoned Si crystals. The A-type defect has an effective carrier capture range of ∼ 40 μm, as determined by EBIC analysis. The activation energy for forming the fast cooling frozen-in defects was estimated to be about 0.31 eV. Hydrogen doping can suppress swirl defect formation but causes other recombination centers. Defect formation can be changed by growth conditions, and long minority charge-carrier lifetimes are achieved through moderately high growth speeds and low thermal gradients during crystal growth, by which both swirl-defects and frozen-in defects are avoided.

We are reporting high performance silicon heterojuncton (SHJ) solar cells fabricated using the hot-wire chemical vapor deposition (HWCVD) technique. On p-type c-Si float-zone wafers, we used an amorphous n/i contact to the top surface and an i/p contact to the back surface to obtain an open circuit voltage (V oc ) of 0.67 V in a 1 cm2 cell with an independent confirmed efficiency of 18.2%. This is the best reported p-type SHJ solar cell, at least by HWCVD. On n-type c-Si float-zone wafers, we used an amorphous (p/i) front emitter and an a-Si:H (i/n) back contact to achieve a Voc of 0.69 V on 1 cm2 cell. We found that proper c-Si surface cleaning prior to the amorphous Si deposition and double-heterojunction is a key to the high Voc. In the heterojunction region, an abrupt interface from c-Si to a-Si:H results in a high Voc; while incorporating a transition to either microcrystalline or epitaxial Si at the c-Si interface results in a low V oc . Lifetime measurement shows that the back surface recombination velocity can be reduced to ~15 cm/s through a-Si:H passivation. Amorphous silicon heterojunction layers on crystalline wafers thus combine low-surface recombination velocity with excellent carrier extraction. The advantages of using HWCVD in comparing with plasma-enhanced CVD are the fast deposition rate and, more important, a wide range of deposition parameters enabling formation of an effective heterojunction with high V oc . Further, the heterojuction cell processing is entirely below 200°C making it one of the few promising low-stress methods for the manufacturing of next generation ultra-thin Si wafer solar cells.

High open-circuit voltage (Voc) silicon heterojunction (SHJ) solar cells are fabricated in double-heterojunction a-Si:H/c-Si/a-Si:H structures using low temperature (p-type c-Si float-zone wafers, we used an amorphous n/i contact to the top surface and an i/p contact to the back surface to obtain a Voc of 667 mV in a 1 cm2 cell with an efficiency of 18.2%. This is the best reported p-type SHJ voltage. In our labs, it improves over the 652 mV cell obtained with a front amorphous n/i heterojunction emitter and a high-temperature alloyed Al back-surface-field contact. On n-type c-Si float-zone wafers, we used an a Si:H (p/i) front emitter and an a-Si:H (i/n) back contact to achieve a Voc of 691 mV on 1 cm2 cell. Though not as high as the 730 mV reported by Sanyo on n-wafers, this is the highest reported Voc for SHJ c-Si cells processed by the HWCVD technique. We found that effective c-Si surface cleaning and a double-heterojunction are keys to obtaining high Voc. Transmission electron microscopy reveals that high Voc cells require an abrupt interface from c-Si to a-Si:H. If the transition from the base wafer to the a-Si:H incorporates either microcrystalline or epitaxial Si at c Si interface, a low Voc will result. Lifetime measurement shows that the back-surface-recombination velocity (BSRV) can be reduced to ~15 cm/s through a-Si:H passivation. Amorphous silicon heterojunction layers on crystalline wafers thus combine low-surface recombination velocity with excellent carrier extraction.

We use in-situ and ex-situ spectroscopic ellipsometry to characterize the optical, electronic, and structural properties of individual layers and completed silicon heterojunction devices. The combination of in-situ measurements during thin film deposition with ex-situ measurements of completed devices allows us to understand both the growth dynamics of the materials and the effects of each processing step on material properties. In-situ ellipsometry measurements enable us to map out how the optical properties change with deposition conditions, pointing the way towards reducing the absorption loss and increasing device efficiency. We use the measured optical properties and thickness of the i-, n-, and p-layers in optical device modeling to determine how the material properties affect device performance. Our best solar energy conversion efficiencies are 16.9% for a non-textured, single-sided device with an aluminum back surface field contact on a p-type float zone silicon wafer, and 17.8% for a textured double-sided device on a p-type float zone silicon wafer.

We report progresses in the development of silicon heterojunction (SHJ) solar cells by hot-wire chemical vapor deposition (HWCVD). A confirmed 18.2% efficiency on a p-type textured wafer has been achieved based on improvements in surface passivation by a-Si:H emitter and back contact as well as in fill factor. The primary objective of high open-circuit voltage (Voc) is achieved by front a-Si:H/c-Si heterojunction optimization, by replacing a conventional Al-alloyed or P-diffused back-surface field with a back c-Si/a-Si:H heterojunction, and by maintaining excellent surface passivation on textured silicon wafers. We first obtain a Voc of 652 mV with a front a-Si:H(n/i) heterojunction emitter on p-type solar cells with an Al back-surface-field (BSF) contact. The high-temperature Al-BSF is then successfully replaced by low-temperature HWCVD-deposited a-Si:H(i/p) layers as the back contact. Lifetime measurement shows the surface recombination velocity (SRV) is reduced to ~15 cm/sec. A higher Voc of 676 mV is obtained with an a-Si:H(n/i) front-emitter and a-Si:H(i/p) back-contact double-heterojunction SHJ solar cell structure, indicating superior back-surface passivation of the textured p-wafer. On n-type silicon wafers, we use an a-Si:H(p/i) front emitter and an a-Si:H(i/n) back contact, to achieve a Voc of 711 mV, the highest voltage obtained by the HWCVD technique so far. Good fill factors are also obtained using the amorphous-phase materials as the back contacts. S-shaped I-V curves are observed if doping cross-contamination are present among different a-Si:H layers or doping level is not enough in the TCO-contacting p-type a-Si:H layer

We use a high-throughput (combinatorial) hot-wire chemical vapor deposition system to passivate the crystal silicon surface and to grow heterojunction silicon solar cells. We study the effectiveness of crystal surface treatments by atomic H or/and NH/sub x/ radicals, followed by the growth of thin hydrogenated amorphous silicon (a-Si:H) films. Treatment and layer properties such as times, thicknesses and gas mixtures can be continuously graded, creating a two-dimensional sample with each variable varying in one direction. This results in high-throughput optimization of the processes. Effective carrier lifetime is measured by photoconductive decay to evaluate the effectiveness of the surface passivation by surface treatments. The effective carrier lifetime increases from about 5 /spl mu/s without passivation to about 24 /spl mu/s with an optimized surface treatment and thickness a-Si:H on single-sided c-Si. Transmission electron microscopy reveals that a-Si:H, a mixed phase, or epitaxial growth of thin-film Si depending upon the surface treatment. Improvement in effective carrier lifetime correlates to with an immediate a-Si:H growth on c-Si, rather than a mixed phase and epitaxial Si growth. We have obtained an efficiency of 13.4% on a non-textured single-sided heterojunction solar cell on a p-type CZ-Si processed with optimized surface treatment.

Thin hydrogenated amorphous silicon (a-Si:H) layers deposited by hot-wire chemical vapor deposition (HWCVD) are investigated for use in silicon heterojunction (SHJ) solar cells on p-type crystalline silicon wafers. A requirement for excellent emitter quality is minimization of interface recombination. Best results necessitate immediate a-Si:H deposition and an abrupt and flat interface to the c-Si substrate. We obtain a record planar HJ efficiency of 16.9% with a high V/sub oc/ of 652 mV on p-type float-zone (FZ) silicon substrates with HWCVD a-Si:H(n) emitters and screen-printed Al-BSF contacts. H pretreatment by HWCVD is beneficial when limited to a very short period prior to emitter deposition.