Search

For SiO

Passivation capping that enhances the photoluminescence (PL) of molecular beam epitaxy (MBE)-grown InAs surface quantum dots (SQDs) is realized by ex situ low-temperature atomic layer deposition (ALD)-grown Al2O3. As the Al2O3 cap thickness increased from 2 to 30 nm, the PL intensity was enhanced by 2.7-fold and the blue shift was suppressed. This is in strong contrast to wet chemistry passivation and in situ GaAs capping by MBE, both of which resulted in significant PL blueshift, due to etching in the former, and In/Ga intermixing and strain in the latter. Atomic force microscopy (AFM) and scanning electron microscopy (SEM) reveal that the Al2O3 cap layer mimics the shape of the underlying SQDs. The cross-sectional transmission electron microscopy (TEM) further reveals that the SQD size and shape remained unchanged after Al2O3 capping, which is in strong contrast to MBE-capping. The passivation mechanisms and native oxide reduction by trimethylaluminum (TMA), including self-clean-up reaction through ligand exchange, are discussed based on the results by x-ray photoelectron spectroscopy (XPS). A detailed comparison between Al2O3 and ZnO cap layers reveals the significance of the cap properties on the SQD size/shape and PL blueshift. While the size/shape of SQDs is preserved by Al2O3 capping, the apex is slightly removed by ZnO capping, resulting in a stronger PL blueshift compared to Al2O3.

Effect of lights with various wavelength on the defect generation in reactive plasma deposition (RPD) process is studied using capacitance–voltage analysis. Indium-tin oxide (ITO) deposition by RPD dramatically decreases the minority carrier lifetime and deteriorates the solar cell performances. The wavelength of light which arrives at the SiO2/Si interface and Si crystal is controlled by varying the SiO2 thickness in SiO2/Si samples. Thick SiO2 layer with above 10 nm prevents the penetration of many ions into the SiO2/Si interface layer, and the only effects of light wavelength on the defect formation are obtained. When SiO2 thickness are 10–600 nm, a large number of defects of the order of 1012 eV−1 cm−2, mid gap energy of Si, are generated by ITO-RPD independent of SiO2 thickness. These defects are expected to be recombination centers. These SiO2 thicknesses are enough thick to completely absorb the light below-110-nm-wavelength. The results suggest that the light of longer wavelength than 110 nm mainly contributes to the defect formation in RPD process. On the other hand, in the case of 500 µm thick SiO2, the generated defects are significantly decreased by one order of magnitude (or decreased to the order of 1010 eV−1 cm−2) small amount of defect is generated. This thick SiO2 prevents the penetration of light with below 180 nm wavelength into the Si. Therefore, the light with around 110–180 nm wavelength, which are generated by Ar and/or O2 plasma in RPD process, mainly forms the recombination-active defects.

This paper presents analytical results for improving crystalline Si solar cells, analyzed using our knowledge in radiation-induced defects in Si. This study suggests that key issues for realizing higher performance Si solar cells are decrease in carbon concentration of less than 1 × 1014 cm−3. Defect introduction rates of Bi–O2i center induced by light illumination are compared with those of Bi–Oi center induced by 1-MeV electron irradiations in this study. Surface recombination velocity degradation of Si solar cells due to 1-MeV electron irradiations is compared with surface degradation of Si solar cells under light illumination by considering Pb center generation.

We investigated the effect of the B2H6 plasma treatment on p-type hydrogenated amorphous silicon (p-a-Si:H) surfaces for high-performance silicon heterojunction (SHJ) solar cells. Secondary ion mass spectroscopy measurements revealed that the boron concentration at the p-a-Si:H surface is increased by employing the B2H6 plasma treatment. Furthermore, specific contact resistance is decreased by about one-third after the B2H6 plasma treatment. No degradation of passivation performance is induced by the B2H6 plasma treatment. The power conversion efficiency of the SHJ solar cells with the B2H6 plasma treatment is improved by the increase in fill factor (FF) due to decreased series resistance and increased shunt resistance. From numerical simulations, the upward band bending is enhanced at the heterointerface between transparent conductive oxide (TCO) and p-a-Si:H by the B2H6 plasma treatment, which is responsible for the improved FF owing to facilitated tunneling holes from c-Si to p-a-Si:H layers and the TCO/p-a-Si:H heterointerface.

A novel liquid cobalt (Co) precursor, bis (diisopropylbutanamidinate)cobalt (DIPRoBA-Co), is proposed as the liquid Co precursor for metal atomic layer deposition (ALD). This precursor was synthesized and the Co ALD process using the obtained precursor was examined. This precursor is liquid and successfully achieves Co ALD with a liquid precursor instead of a solid one. Transmission electron microscopy observation shows that 5–6 nm thick Co metal film grows on a plasma silicon dioxide substrate step structure by this ALD using an ammonia, hydrogen and DIPRoBA-Co gas system with 80 cycles at 220 °C substrate temperature.

Defects such as oxygen vacancy in the nanostructures have paramount importance in tuning the optical and electronic properties of a metal oxide. Here we report the growth of oxygen deficit tungsten oxide (W18O49) nanorods modified with ruthenium oxide (RuO2) using a simple and economical hydrothermal approach for energy storage application. In this work, a novel approach of hybridizing the W18O49 nanostructure with RuO2 to control the electrochemical performance for energy storage applications has been proposed. The result displays that the hybridization of the nanostructures plays an important role in yielding high specific capacitance of the electrode material. Due to the augmentation of W18O49 and RuO2 nanostructures, the galvanostatic charging and discharging (GCD) mechanism exhibited the transformation from the battery type characteristics of W18O49 into the typical pseudocapacitor feature of hybrid architect nanostructure due to defect creations. The electrochemical measurement of hybrid nanomaterial shows the doubling of specific capacitance to 1126 F/g and 1050 F/g in cyclic voltammetry (CV) and GCD, respectively, in comparison with W18O49 and RuO2 and earlier reports. The enhancement in the stability performance up to 3000 cycles of hybrid is indebted to the stable nature of W18O49 and the high conductivity of RuO2.

The behavior of oxide precipitates during solar cell fabrication processes and the resulting effect on device performance have been investigated by transmission electron microscopy (TEM) observation. Samples were prepared with different carbon concentration and under different crystal growth conditions, namely using the conventional and an advanced process. The density of oxide precipitates increased monotonically with the carbon concentration, while the cell efficiency improved with decreasing oxygen precipitate density. When the carbon concentration was reduced to below 1016 cm−3, the oxide precipitates grew largely and dislocations were introduced. TEM observations confirmed that the morphology of the oxide precipitates clearly differed depending on the crystal growth conditions. Precipitates grown in platelet form introduced high density dislocations in their surroundings, while the dislocation density was relatively lower around polyhedral-type precipitates. These results thus reveal that oxygen precipitation can be controlled by varying the crystal growth conditions, possibly contributing to the production of high-efficiency solar cells.

The development of photovoltaics (PV)-powered vehicles are expected to contribute to reduce CO2 emission of vehicles and create a clean energy society. This paper presents the impact of high-efficiency solar cell modules on reduction in CO2 emission, charging cost reduction for electric vehicles, and reducing storage capacity of PV-powered electric vehicles. In this paper, the effects of solar cell module efficiency upon driving distance of PV-powered vehicles are also shown. Especially, the potential of Si tandem solar cells for PV-powered vehicle applications is discussed. This paper presents that the III-V/Si 3-junction solar cell modules with an efficiency of more than 37% have the potential of longer driving distance of 30 km/day average and more than 50 km/day on a clear day compared to an average 16 km/day driving by vehicles powered by 20% efficiency Si solar cell modules.

In this work, we have successfully proclaimed the importance of defect prone nanostructure on to the electrode surface for the promising glucose sensing applications. Oxygen-deficient W18O49 moieti...

The cost of solar cell production can be reduced by wafer thinning. A thinner wafer provides flexibility, and crystalline silicon solar cells are promising as flexible solar cells due to their flexibility. However, as wafers become thinner, production yield decreases due to wafer breakage caused by sawing damage; thus, to further reduce wafer thickness, it is necessary to suppress sawing damage. We investigated the flexibility of wafers under various slice conditions by conducting biaxial bending tests and clarified the dominant factor causing sawing damage to further reduce the wafer thickness for crystalline silicon solar cells. The results of damage observation by scanning electron microscopy and evaluation of the crystal structure by Raman spectroscopy confirm that the damage structure changes significantly depending on wire specifications. The results from the biaxial bending tests indicate that the three-dimensional flexibility of a wafer is determined by wire specifications.

Sodium (Na) and lithium (Li) in the silver (Ag) paste cause the potential-induced degradation (PID), while the PID of p-type crystalline silicon (Si) photovoltaic modules is caused by Na in the front cover glass. Some Ag pastes contain these elements to control the firing properties in solar cells fabrication. In order to eliminate the effect of Na and other elements in the front cover glass on PID, PID tests for crystalline Si photovoltaic modules without front cover glass and using cells with various electrode pastes of controlled additive contents were performed. When the Ag paste with Na is used, the shunt resistance decreases and the PID occurs. This phenomenon is similar to that induced by Na in the front cover glass, but, it requires the shorter time duration as compared with the case of Na in the front cover glass. In addition, it is found that Li in the paste also causes the PID equivalent to that by Na in the paste.

We have investigated the chemical and electrical properties of a thin SiO2/TiO2 stacking layer deposited on n-Si and heavily phosphorus-doped n++ Si substrates to elucidate effects of phosphorus doping of Si absorbers on the band alignment and electrical performance of a SiO2/TiO2 stack-based electron-selective contact deposited on the differently doped Si substrates. From our XPS study, we show a shift of the TiO2 energy levels up to ~0.13 eV with respect to those of Si as the doping level of Si substrates changes. We also show that the conduction band offset of the SiO2/TiO2 stacking layer at the interface with the n++ Si substrate seems to smaller than that of the SiO2/TiO2 stacking layer at the interface with n-Si substrate. Finally, from our electrical transport measurements, we could conclude that the thinner tunneling barrier, the increased electron density in front of the SiO2 layer in the n++ Si surface, and/or the reduced barrier height by heavy doping, seem to enhance the majority electron transport property of the SiO2/TiO2/n++ Si samples compared to that of the SiO2/TiO2/n-Si samples.

In pursuit for the improvement of heterojunction Si solar cell performance, we evaluated Sn-doped Indium oxide (ITO)/a-Si structure by using conventional and hard X-ray photoelectron spectroscopy (XPS, HAXPES) to identify the cause of solar cell performance degradation. HAXPES allows us to evaluate the SiOx layer at the ITO/a-Si interface non-destructively. The SiOx formation at the ITO/a-Si interface leads to an increase the contact resistance, which can be reduced by post deposition annealing (PDA). In addition, PDA promoted the evaluation of Fermi level, the precipitation of ITO component in a-Si layer, and the increase of interface roughness. Before PDA, the diffusion of Sn atoms in a-Si was observed. Furthermore, it was also confirmed by PDA that Si atoms were diffused to ITO. These reaction at the ITO/a-Si interface may be part of the degradation factor of the Si solar cells.

We have developed a rapid ELO technique using mechanical cleavage via 2D-layered metal selenide inserted between the III-V epitaxial layer and the substrate. In this technique, processing time is only a few seconds. The key issue is the crystal quality improvement of the GaAs layer. As 2D-layered metal selenide, double 2D-buffer layers of GaSe and In2Se3 were grown on Si(111) substrate by MBE. The 180o rotational twin formation and dislocations in GaAs layer were characterized by XRD pole figure and cross-sectional TEM. The twin ratio was estimated to 12%. These twin domains are mainly distributed near the bottom interface. To reduce dislocation density, it is necessary to suppress the twin formation at the interface.

Development of high-efficiency solar cell modules and new application fields such as PV (Photovoltaics)-powered vehicles are significant for the further development of PV and the creation of new clean energy infrastructure based on PV. In this paper, analytical results for impact of high-efficiency solar cell modules on increasing driving distance, reducing CO 2 emission and saving charging cost of electric vehicles by PV-powered vehicles. Because the Si tandem solar cells are expected to have significant potential for PV-powered vehicle applications, potentials of high-efficiency and driving distance are also analyzed. The III-V/Si 3-junction solar cell modules have potential of driving distance of 30 km/day average and more than 50 km/day on a clear day.

In this work, we have successfully proclaimed the importance of defect prone nanostructure on to the electrode surface for the promising glucose sensing applications. Oxygen-deficient W

Defects such as oxygen vacancy in the nanostructures have paramount importance in tuning the optical and electronic properties of a metal oxide. Here we report the growth of oxygen deficit tungsten oxide (W

The III-V compound solar cells have contributed as space and concentrator solar cells and are important as sub-cells for multi-junction solar cells. This paper reviews progress in III-V compound single-junction solar cells such as GaAs, InP, AlGaAs and InGaP cells. In addition, analytical results for non-radiative recombination and resistance losses in III-V compound solar cells are shown for further understanding and reducing major losses in III-V compound materials and solar cells.

In this study, we evaluated sawing damage of thin silicon wafers. Ultra-thin silicon wafers with great advantages of bendability and lightweight are suitable for needs such as to realize PV-powered vehicles. For thin wafers, it is important to realize high precision slicing to prevent breakage. We evaluated the distribution of sawing damage and crystallinity in order to clarify the cause of wafer breakage and establish low damage slice conditions. We confirmed phase transformation of silicon and crystalline defects on wire exit side on the conventional slicing surface, while the advanced slicing surface shows almost only single-crystalline Si phase.

Recently, titanium oxide has been widely investigated as a carrier-selective contact material for silicon solar cells. Herein, titanium oxide films were fabricated via simple deposition methods involving thermal evaporation and oxidation. This study focuses on characterizing an electron-selective passivated contact layer with this oxidized method. Subsequently, the SiO2/TiO2 stack was examined using high-resolution transmission electron microscopy. The phase and chemical composition of the titanium oxide films were analyzed using X-ray diffraction and X-ray photoelectron spectroscopy, respectively. The passivation quality of each layer was confirmed by measuring the carrier lifetime using quasi-steady-state photoconductance, providing an implied open circuit voltage of 644 mV. UV&ndash, vis spectroscopy and UV photoelectron spectroscopy analyses demonstrated the band alignment and carrier selectivity of the TiO2 layers. Band offsets of ~0.33 and ~2.6 eV relative to the conduction and valence bands, respectively, were confirmed for titanium oxide and the silicon interface.

The development of high-performance solar cells offers a promising pathway toward achieving high power per unit cost for many applications. Because state-of-the-art efficiencies of single-junction solar cells are approaching the Shockley-Queisser limit, the multi-junction (MJ) solar cells are very attractive for high-efficiency solar cells. This paper reviews progress in III–V compound single-junction and MJ solar cells. In addition, analytical results for efficiency potential and non-radiative recombination and resistance losses in III–V compound single-junction and MJ solar cells are presented for further understanding and decreasing major losses in III–V compound materials and MJ solar cells. GaAs single-junction, III–V 2-junction and III–V 3-junction solar cells are shown to have potential efficiencies of 30%, 37% and 47%, respectively. Although in initial stage of developments, GaAs single-junction and III–V MJ solar cells have shown low ERE values, ERE values have been improved as a result of several technology development such as device structure and material quality developments. In the case of III–V MJ solar cells, improvements in ERE of sub-cells are shown to be necessary for further improvements in efficiencies of MJ solar cells.

We have investigated the effects of chemical rounding (CR) on the surface passivation and/or antireflection performance of AlOx- and AlOx/SiNx:H stack-passivated pyramid textured p+-emitters with two different boron doping concentrations, and on the performance of bifacial n-PERT Si solar cells with a front pyramid textured p+-emitter. From experimental results, we found that chemical rounding markedly enhances the passivation performance of AlOx layers on pyramid textured p+-emitters, and the level of performance enhancement strongly depends on boron doping concentration. Meanwhile, chemical rounding increases solar-weighted reflectance (RSW) from ∼2.5 to ∼3.7% for the AlOx/SiNx:H stack-passivated pyramid textured p+-emitters after 200-sec chemical rounding. Consequently, compared to non-rounded bifacial n-PERT Si cells, the short circuit current density Jsc of 200-sec-rounded bifacial n-PERT Si cells with ∼60 and ∼100 Ω/sq p+-emitters is reduced by 0.8 and 0.6 mA/cm2, respectively under front p+-emitter side illumination. However, the loss in the short circuit current density Jsc is fully offset by the increased fill factor FF by 0.8 and 1.5% for the 200-sec-rounded cells with ∼60 and ∼100 Ω/sq p+-emitters, respectively. In particular, the cell efficiency of the 200-sec-rounded cells with a ∼100 Ω/sq p+-emitter is enhanced as a result, compared to that of the non-rounded cells. Based on our results, it could be expected that the cell efficiency of bifacial n-PERT Si cells would be improved without additional complicated and costly processes if chemical rounding and boron doping processes can be properly optimized.

Efficiency potential of crystalline Si solar cells is analyzed by considering external radiative efficiency (ERE), voltage, and fill factor losses. Crystalline Si solar cells have an efficiency potential of more than 28.5% by realizing ERE of 20% from about 5% and normalized resistance of less than 0.05 from around 0.1. Nonradiative recombination losses in single-crystalline and multicrystalline Si solar cells are also discussed. Especially, nonrecombination and resistance losses in multicrystalline Si solar cells are shown to be higher than those of single-crystalline cells. Importance of further improvement of minority-carrier lifetime in crystalline Si solar cells is suggested for further improvement of crystalline Si solar cells. High efficiency of more than 28.5% will be realized by realizing high minority-carrier lifetime of more than 30 ms. Key issues for those ends are reduction in carbon concentration of less than 1 × 1014 cm−3, oxygen precipitated and dislocations even in single-crystalline Si solar cells, and reduction in dislocation density of less than 3 × 103 cm−2 in multicrystalline Si solar cells.

The current research focuses on the Intracellular biosynthesis of Ag/AgCl nanohybrids in microalgae, Scenedesmus sp. The effect of biosynthesis process on growth and lipid profile of cells is key element of this study. Ag/AgCl nanohybrids synthesized intracellularly were characterized by UV–Vis spectrophotometer, Powder X-Ray Diffraction (P-XRD), Scanning Electron Microscopy (SEM), High Resolution Transmission Electron Microscopy (HRTEM). 10–20 nm and 10–50 nm sized spherical shaped nanoparticles of polycrystalline nature were grown using 0.5 and 1 mM of AgNO3 precursor, respectively and Scenedesmus sp. as reducing agent. Total lipid content of the cells treated with 0.5 mM and 1 mM AgNO3 was static and found to be 43.2 ± 0.01 μg/mL and 48.2 ± 0.02 μg/mL respectively at 120 h of Ag/AgCl nanoparticles biosynthesis. FAME (Fatty Acid Methyl Ester) profile was improved due to intracellular nanoparticles biosynthesis with maximum C16:0 (palmitic acid) (35.7%) in cells treated with 0.5 mM AgNO3 used for Ag/AgCl nanohybrids synthesis. Palmitic acid in cells exposed to 0.5 mM concentration of metallic precursor increased by 75.86%. Synthesized nanoparticles were tested on four bacterial strains to establish its antibacterial efficiency showing appropriate zone of inhibition at varying concentrations. Present study efficiently demonstrates the utility of microalgae integrating nanoparticles biosynthesis and lipid accumulation.

We investigated the degradation factor of the conversion efficiency of the silicon heterojunction solar cells. In particular, we clarified the effect of the transparent conductive oxide film deposition conditions on the film quality and interface states, and the relationship between these factors and the conversion efficiency. Heat process causes a decrease in carrier mobility due to a decrease in the grain size of the TCO film, but has an effect of improving the TCO/a-Si:H(p) interface states. In particular, the silicon oxide layer between the TCO film and a-Si:H(p) increases the series resistance and moderates the band bending at the TCO/a-Si:H(p) interface, leading to FF degradation. Since In2O3:H film easily forms a silicon oxide layer at the TCO/a-Si:H(p) interface, the interface treatment is important factor in the cell manufacturing process.