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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.

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.

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.

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.

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.

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.

In this paper, we propose a new method of using H2 supply in the atmosphere to increase Sn concentration in a Ge1−xSnx film epitaxially grown on a Ge substrate using MOCVD (metal organic chemical vapor deposition). H2 supplied in the atmosphere accelerates decomposition of Sn precursors and suppresses surface migration of Sn atoms during epitaxial growth of a Ge1−xSnx film. The proposed method is new and fundamentally different from the existing methods that increase Sn concentration through either crystallizing α-Ge1−xSnx or lowering growth temperature. The proposed method uses H2 supply in the atmosphere to increase Sn concentration. In order to show the effectiveness of the proposed method, we conducted experiments with varying ratios of supplying H2 in the atmosphere and epitaxially grew a Ge1−xSnx film on a Ge substrate using MOCVD. MO precursors that we used in our experiments (tertiarybutylgermane and tetraethyl tin) are new and safe. In our experiments, we observed that Sn concentration increased with H2 supply during growth, while maintaining a high growth rate of a Ge1−xSnx film.

We have investigated effects of different tunnel oxide layers on the performance and light stability of tunnel oxide/TiO 2 stack electron-selective contacts on n-type Si. From XPS analysis, we found that chemical properties of a SiO x interlayer at an interface between a tunnel oxide/TiO 2 stack electron-selective contact and an n-type Si significantly depend on stack materials and fabrication processes of tunnel oxide layers. We also found that although chemical SiO 2 and thermal atomic layer deposited AlOx tunnel layers show higher passivation performance, plasma-enhanced atomic layer deposited AlO x tunnel layers demonstrate light-enhanced τ eff with an ITO capping layer as well as the highest light stability without an ITO capping layer.

In this paper, we report on the fabrication of Ta-doped TiO2 (TiO2:Ta) electron-selective contacts and their improved passivation qualities. By using thermal atomic layer deposition, 3.5 nm-thick, undoped TiO2 films and 3.5 nm-thick TiO2:Ta films with Ta concentrations of 1.5, 2.8, and 5.5 at.% were formed at 150 °C on n-type crystalline silicon substrates with ∼1 nm-thick chemical SiO2 layers. Rutherford backscattering spectroscopic measurements confirmed the Ta concentrations in the films and uniform distributions of Ta atoms in the films. X-ray photoelectron spectrometry measurements implied that Ta atoms rather cause local structural changes than enter substitutionally into Ti sites. After annealing at 130 °C in air, the effective minority carrier lifetime (τ eff) of the TiO2:Ta-passivated samples were significantly higher than those of the samples passivated with undoped TiO2 films. The highest τ eff was obtained for the samples with a relatively low Ta-doping concentration of 1.5 at.%. On the other hand, the passivation quality was degraded by Ta doping with a too high concentration (for example, 18.4 at.%). These results indicate that moderate Ta doping improves the passivation quality of TiO2 thin films.

The theoretical lateral current of the surface inversion layer in a crystalline silicon (cSi) surface for a p-aSi:H/i-aSi:H/cSi heterojunction (SHJ) solar cell was calculated using computer simulation and was compared with the experimental one to study defects/traps at the aSi:H/cSi interface and/or in the cSi surface and to detect the acceptor concentration (N a) in p-aSi:H. To experimentally extract the lateral surface inversion layer current, a field-effect transistor type test element group device was co-integrated with SHJ cells on the same wafer. From the correlation between the experimental and calculated lateral surface inversion layer current, the density of defects/traps (D it) at the aSi:H/cSi interface and/or in the cSi surface and the value of N a were extracted. The calculated lateral surface inversion layer current stayed unchanged for various minority carrier lifetimes in the substrate, suggesting that this method is not suffered from the variation in the material parameters in the substrate.

We demonstrate that the passivation quality of TiO2 electron-selective contacts can be improved by Ta doping. By using atomic layer deposition, 3.5-nm-thick, undoped TiO2 films and Ta-doped TiO2 (TiO2:Ta) films with Ta concentrations of 1.5, 2.8, and 5.5 at.% were formed on n-type crystalline silicon substrates with chemical SiO2 layers. After annealing at 130 °C, the effective minority-carrier lifetime (τeff) of the TiO2:Ta-passivated samples were significantly higher than that of the undoped-TiO2-passivated samples, and the highest τeff was obtained at a relatively low Ta-doping concentration of 1.5 at.%. These indicate that moderate Ta doping improves the passivation quality of TiO2 thin films.

The growth orientation dependence of N incorporation on traditional (100) and high-index GaAs (311)A/B planes has been investigated by the first principle calculation and experimental measurement. Due to the electronegativity and atomic radius differences between As and N atoms, the Ga N bond is much shorter than the corresponding Ga As bond as N occupies As atom site. The optimization to energetically preferred construction leads to the inward moving of N atom, while the displacement extent of three surface models exhibits considerable differences. More importantly, the theoretical result reveals a lower formation energy of N doping for N@(311)B GaAs surface and a larger one for N@(311)A GaAs surface as compared with the traditional (100) GaAs plane. The first principle investigations thus suggest the enhanced N incorporation in (311)B GaAsN, which is in good accordance with the secondary ion mass spectrometry (SIMS) measurement results of GaAsN layers by chemical beam epitaxy (CBE).

The paper presents a quantitative approach to the investigation and comparison of the material qualities of III-V on silicon (III-V/Si) solar cells by using external radiative efficiencies. We use this analysis to predict the limiting efficiencies and evaluate the criteria of material quality in order to achieve high efficiency III-V/Si solar cells. This result yields several implications for the design of high efficiency III-V/Si solar cells.

In this paper, the Chemical Beam Epitaxy approach to GaAsN material growth has been investigated. Photoluminescence and Hall effect measurements were performed to clarify the influence of defects on the transport properties, those of holes in particular. The PL intensity of near-band emission (1.35 eV-peak) for GaAs0.996N0.004 at low temperature ( 1) indicated that the N atoms were alloyed in a disordered arrangement. As a result, the corresponding alloy scattering mechanism was enhanced, contributing to the hole mobility decrease. However, compared to p-type GaAsN grown by MBE or MOCVD, our CBE-grown GaAsN showed a higher value of hole mobility.

This research investigates the cause of lifetime reduction properties of a crystalline defect layer introduced by the plasma process such as reactive plasma deposition (RPD). The plasma irradiation damage to silicon substrate with the different oxygen and carbon concentrations were evaluated. Minority carrier lifetime of the silicon substrate after the RPD process has been significantly reduced by plasma irradiation. Furthermore, photoluminescence (PL) spectroscopy revealed that the cause of the lifetime degradation on the silicon substrate is Ci–Oi defect generation originated in the plasma irradiation during the RPD process.

GaAs were grown by the migration-enhanced epitaxy (MEE) method on vicinal (001) Si substrates oriented 4 ° off towards [110] at low temperature. Investigations of crystalline and optical properties of the grown GaAs/Si were carried out by the methods of X-ray diffraction (XRD) and low-temperature photoluminescence (PL). The possible cause for tilting in the GaAs grown at low-temperature is discussed.

We have investigated the effects of chemical rounding on the performance of bifacial n-PERT Si cells with a random-pyramid textured p+-emitter. From experimental results, we found that solar-weighted reflectanceR SW of pyramid textured p+-emitters passivated with an ${AlO}_{x}/{SiN}_{x}$:H stack increases and short circuit current densityJ sc of bifacial n-PERT Si cells with an ${AlO}_{x}/{SiN}_{x}$:H stack-passivated textured p+-emitter consequently decreases as a function of chemical rounding time. However, the loss inJ sc is fully offset by the increased fill factor FF, and the efficiency of the 200-sec-rounded cells is consequently enhanced, compared to the non-rounded cells. In addition, the deposition of an indium tin oxide layer on the non-rounded and rounded $p^{+}-$ emitters passivated with an ${AlO}_{x}/{SiN}_{x}$:H stack can reduce reflectance largely in the near-infrared region. Based on the experimental results, although we would need further studies, it could be expected that cell efficiency of a bifacial ${n}$-PERT Si bottom cell and its monolithic tandem cell with a perovskite top cell would be improved without additional complicated and costly processes if chemical rounding and boron doping processes are properly optimized.

We investigated the damage using hard X-ray photoemission spectroscopy (HAXPES), and found that the a-Si surface was oxidized due to the energetic oxygen ambient during the deposition. For the conventional and advanced sputter, the SiO peak intensity at the ITO/a-Si interface did not change by post deposition annealing, but for RPD the peak intensity decreased. From the O 1s and In 3d spectra, it is considered the oxygen at the ITO/a-Si interface moved to the oxygen deficient in ITO. We also verified the damaged oxide was partially recovered by the post deposition annealing process.

Lifetime degradation caused by oxygen precipitates combined with metal contamination in Cz-Si for solar cells was evaluated for the samples with different interstitial oxygen concentrations using PL imaging and IR–LST. It was confirmed that phosphorus diffusion gettering is effective for the samples with low oxygen concentration, however the lifetime never recovered for the samples with high oxygen concentration. The enhanced oxygen precipitation process made it more difficult to recover from the metallic contamination. We believe the high density and large size oxygen precipitates are harmful for the lifetime in combination with metal impurities.

Effects of an ITO capping layer on the interface workfuncion of MoO x was studied for an ITO/MoO x /SiO2/Si structure device from the viewpoint of the behavior of In atoms. The workfunction of MoO x at the MoO x /SiO 2 interface, which were extracted by capacitance-voltage (C-V) analysis, was largely different from the bulk MoO x film in its value and post-deposition forming gas annealing (PDFGA) temperature dependency. The interface workfunctoin decreased by 0.13 and 0.35 eV by 200 and 400 °C PDFGA, respectively, while bulk workfunction decreased by only 0.1 eV by 400 °C PDFGA. A secondary ion mass spectroscopy (SIMS) analysis showed that In atoms were penetrated from the ITO layer into the MoO x layer by PDFGA. The concentration of In near the MoO x /SiO 2 interface increased from ∼1019 cm−3 for the as-grown ITO sample to ∼1020 cm−3 for the sample with 400 °C PDFGA. The increase in the In concentration near the MoO x /Japan>SiO 2 interface is a possible cause to decrease the interface workfunction.

The properties of the acceptor states in GaAsN grown by chemical beam epitaxy (CBE) are studied by analyzing their charges based on the Poole–Frenkel model. Deep level transient spectroscopy (DLTS) shows two acceptor levels at 0.11 and 0.19 eV above the valence band maximum. The emission rates of carriers from these states are enhanced with increasing the electric field during the DLTS measurement, which indicates that the energies required for the emission are decreased. By analyzing this field-enhanced emission process, the polarizabilities of the levels at 0.11 and 0.19 eV are found to be −1 (±0.1) and −2 (±0.1), respectively. In addition, these states have almost the same concentration. Therefore, we conclude that they originate from the same defect, acting as a double acceptor in GaAsN film grown by CBE.

The N–H related acceptor defects in GaAsN grown by chemical beam epitaxy (CBE) are studied by hydrogen isotopes, H and D. When the films are grown by a conventional arsenic source, deep level transient spectroscopy (DLTS) reveals two energy levels at 0.11 and 0.19 eV above the valence band. These levels were considered to act as a double acceptor in the literature. When the films are grown by a deuterated arsenic source, new signals appear in DLTS spectra at 0.15 and 0.23 eV. This indicates that the new signals are originated from D-related defects. The energy differences between 0.15 and 0.11 eV, and that between 0.23 and 0.19 eV are same (0.04 eV). Although these energy levels become deeper with increasing the growth temperature, the energy differences are almost constant independent of the growth condition. In addition, the intensity ratios of the peaks at 0.15 (0.23) eV to that at 0.11 (0.19) eV have a good correlation with the isotopic concentration ratio of D to H in the grown films. Therefore, we conclude that the energy differences and intensity ratios of the DLTS peaks occur due to the structural change from N–H to N−D in the same type of defect, and that this acceptor is an N–H related defect.

Combining Si PV module technology with an efficient III- V CPVs top PV into a tandem device is an attractive approach to enhance the efficiency of PV modules. Here, a method called III- V/Si hybrid configurations for enhancing the Si module efficiency is placing III- V static CPVs at the edge gap of each Si wafer rather than stacking in the top of Si. The prototype PV module shows the enhancement of efficiency. The cost evaluations of the III- V lSi hybrid configurations compared with Si module is discussed under various presumed cost ratio of 111-V/Si PVs.

The behavior of oxygen precipitates under solar cell fabrication processes and the effect on device performance were investigated using TEM observation. Samples were prepared with different carbon concentration and with two sets of growth conditions. The number of precipitates correlates monotonically with the carbon concentration. When the initial carbon concentration is high, the cell efficiency is improved by decreasing the carbon concentration. When the initial carbon concentration is reduced to smaller than 1016 cm−3, the oxygen precipitate grows largely and introduces dislocation. Precipitates grown in a plate form introduce dislocations to the surroundings at a high density, while dislocation density is relatively small around the precipitates polyhedral-grown on the basis of an octahedron. Under the growth conditions for introducing a plate-like precipitate, the cell efficiency was not improved even if the carbon concentration was reduced.

The high quality and thin Si wafer technology for the future higher conversion efficiency and lower cost crystalline silicon solar cells are realized. The high minority carrier lifetimes even after the processes are obtained by controlling the Czochralski growth condition, which prevents the interstitial oxygen segregation enhanced by the substitutional carbon. The Cz ingot is sliced by the advanced diamond multi-wire saw technology and the thin wafers with relatively thin damaged layer and 100μm kerf-loss are realized. The thin wafer with low kerf-loss decreases the wafer cost and improve the cell performance. The thin wafer solar cells are fabricated using the PERC processes, and these technologies are evaluated from the view point of photovoltaic.

We applied aluminum-induced crystallization (AIC) as a technique to realize heavily doped p-type polycrystalline Si layer at low temperature for the rear side of tunnel oxide passivated contact concept solar cell. Systematic temperature variation of AIC revealed that annealing at a temperature slightly lower than the eutectic temperature (577°C) is effective to improve solar cell performance. This is explained by reduced resistivity for low contact resistance while avoiding meltinz of AI-Si.

By stacking a III - V cell to the Si cell, it is expected to reach to more than 30 % of efficiency. However, the contribution of the Si bottom cell may be reduced to 5 to 6 % in maximum. Another problem is that the III-V cell cost is still expensive and high concentration without relying on tracking is expected. For solving these two problems, a new configuration that places small III-V multi-junction solar cells at four corners of a single-crystalline Si solar cell was invented.

Adding SiCl4 to the atmosphere during the growth of a crystal suppressed crystalline defects and impurities from the edge of silicon ingots. Crystalline silicon ingots with seed crystal were grown by using the unidirectional solidification technique. Most of the grain boundaries were inactive Σ3 in the ingot with the SiCl4 injection. There were no small-angle grain boundaries at the top and edge of ingots. The carbon concentration with SiCl4 was decreased to less than half of that without the SiCl4 injection. Carbon precipitation did not occur even at the surface of ingots and the surface of grown ingots had a metallic luster.

The two N-H local vibrations in GaAsN grown by the chemical beam epitaxy have the same preferential orientation in the crystal. The bond orientations of the N-H wagging mode at 961 cm-1 and stretching mode at 2952 cm-1 tend to align along [1-10]. The peak intensities of the three major N-H local vibration modes were examined by the polarized Fourier transform infrared spectroscopy. The integrated absorption peaks at 961and 2952 cm-1 showed the two-fold rotational symmetry in (001) plane, while the one at 3098 cm-1 was almost constant within the accuracy of this measurement. The maximum peak intensities were observed when the IR polarization direction was [110] for the N-H wagging mode at 961 cm-1, and [1-10] for the N-H stretching mode at 2952 cm-1, which means that those bond orientations projected on (001) plane were the same. The result indicates that the N-H wagging mode at 961 cm-1 and stretching mode at 2952 cm-1 are originated from the same N-H bond. (© 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

To get the optimized condition and ideal furnace structure, we have performed seed cast growth of mono-crystalline Si by using unidirectional solidification furnace. More than 20 ingots of 10 cm diameter and 10 cm height were grown under different growth conditions. The quality of ingots was characterized by using Fourier transform infrared spectroscopy (FTIR), infrared microscopy, scanning infrared polariscope (SIRP), X-ray topography, etc. We have realized reduction of carbon, residual strain and extended defects, which may contribute the increase of solar cell efficiency.

The dependence of solar cell parameters on i-aSi:H (non- or lightly-doped hydrogenated amorphous silicon) layer thickness in an aSi:H/cSi (crystalline silicon) heterojunction solar cell was analyzed using numerical simulation. By considering the quantum confinement effect at interfaces between i-aSi:H and cSi, experimental data which had not been explained by simulation could be successfully interpreted. The mechanism of an open-circuit voltage increase was visually presented by analyzing carrier distributions and quasi-Fermi levels near cSi surfaces and in the i-aSi:H layers. The optimized thicknesses of the i-aSi:H layers in both front and rear junctions were suggested to obtain the maximum conversion efficiency. The influences of the quantum confinement effect on the simulation results were discussed.

The effect of the tridimethylaminoarsenic (TDMAAs) source flow rate on the electronic signature as well as on the trapping density of electron traps in undoped n-type GaAsN grown by chemical beam epitaxy was investigated by deep level transient spectroscopy and isothermal capacitance transient spectroscopy methods. It was found that the densities of four electron traps, E1 to E4, localized at average energy depths of 0.05, 0.11, 0.16, and 0.39 eV, respectively below the bottom edge of the conduction band, significantly decrease with increasing TDMAAs up to 1.2 sccm. Nevertheless, the decrease of trapping density for these energy states showed quite different behaviors. This result implies that the excess of As atoms in the alloy could limit the formation of these electron traps. Furthermore, it indicates that the degradation of the optoelectronic properties of the alloy is not only caused by the addition of N atom to the lattice of GaAs. An interesting feature of this result is the possibility of recovering the lifetime of minority carriers in p-type GaAsN material, and, therefore, enhancing the conversion efficiency of GaAsN based solar cells. (© 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Current transport mechanisms were investigated in a GaAsN homojunction solar cell (HJSC) grown by chemical beam epitaxy. At each temperature of measurement, the current-voltage (I–V) characteristics were found to deviate from the diffusion model. The fitting of these characteristics affirmed that the recombination current in the space charge region of the HJSC is mainly attributed to a localized state at 0.31 eV below the bottom edge of the conduction band of GaAsN. This recombination center was identified by deep level transient spectroscopy. It was previously confirmed to act as a nitrogen-related non-radiative recombination center and the split interstitial formed from one nitrogen atom and one arsenic atom in a single V-site (N-As) As was tentatively suggested to be its possible origin. The lifetime of electrons from the conduction band to its energy level was calculated to be around ∼0.20 ns, using the Shockley-Read-Hall model for trap-assisted recombination process. Furthermore, such order of magnitude was confirmed by time-resolved photoluminescence measurements.

The dominant electron scattering mechanisms in GaAsN were investigated by analysing the Hall electron mobility and photoluminescence (PL) spectrum. The GaAsN thin films were grown by chemical beam epitaxy. The temperature dependence of the electron mobility indicated that polar optical phonon (POP) scattering was dominant in GaAs and GaAs:N0.0003 near room temperature. By increasing nitrogen compositions up to around 0.1%, the temperature dependence of the electron mobility became from T-1.23 to T-0.5. It indicated that the dominant scattering changed from POP to alloy scattering with nitrogen composition. The full width at half maximum of the PL spectra suggested that the large potential fluctuation at conduction band edge did not exist in GaAsN grown by chemical beam epitaxy. The theoretical electron mobility of POP and alloy scattering with large effective mass which was obtained by Masia et al., Dennecker et al., and Ibanez et al. agreed with the determined electron mobility. Therefore, the POP and alloy scattering with the large effective mass were considered to be the origin of the low electron mobility of GaAsN. (© 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

The temperature dependence of capacitance–voltage ( C – V ) and current voltage ( I – V ) characteristics were used to study the cause of high background doping and the underlying current transport mechanisms in GaAsN Schottky diode grown by chemical beam epitaxy (CBE). In one hand, a nitrogen-related sigmoid increase of junction capacitance and ionized acceptor concentration was observed in the temperature range 70–100 K and was attributed to the thermal ionization of a nitrogen–hydrogen-related deep acceptor-state, with thermal activation energy of approximately 0.11 eV above the valence band maximum (VBM) of GaAsN. This acceptor state is mainly responsible for the high background doping in unintentionally doped GaAsN grown by CBE. On the other hand, the I – V characteristics at different temperatures were found to deviate from the well known pure thermionic-emission mechanism. Based on their fitting at each temperature, the recombination current in the space charge region of GaAsN Schottky diode was mainly attributed to a hole trap, localized at 0.51 eV above the VBM. Given the accuracy of measurements, this result was confirmed by deep level transient spectroscopy measurements. Nevertheless, considering the Shockley–Read–Hall model of generation-recombination, the recombination activity of this defect was quantified and qualified to be weak compared with the markedly degradation of minority carrier lifetime in GaAsN material.

Conductive paste degrades the solar cell performance due to the metallization. Silver crystallites at the interface may shunt the p-n junction, which degrades the cell performance. Besides, it is conceivable that glass frit itself should not effectively damage silicon, but there is no clear evidence for the proof. In this study, the “floating contact method” proposed by R. Hoenig is used to evaluate the effects of glass frit by making the floating contacts with the glass frit. It is conclude that glass frit itself causes shunts and increases the saturation current, which corresponds carrier recombination beneath the glass frit contacts.

A new class of passivation material, ternary Al x Mg 1−x O y is developed and its surface passivation and interface properties on silicon surfaces are investigated in this study. Super-cycle plasma-enhanced atomic layer deposition is employed to fabricate Al x Mg 1−x O y thin films and can effectively engineer physical properties of the thin films. Our study also shows that the developed Al x Mg 1−x O y can provide excellent surface passivation on p-type silicon as indicated by very low S eff , max of ∼1.8 cm/s after annealing. The observed excellent passivation quality seems to be due to enhanced interface properties (i.e. enhanced Q eff and D it ) by Mg ion doping into AlO x .

We present the measurement results and analyses of a InGaP/GaAs//Si mechanical stack four-terminal solar cell. From these results, we performed detailed discussions of the loss mechanisms and efficiency limits of InGaP/GaAs//Si mechanical stack solar cells.

Quantum confinement effect in the nanocrystal-Si (nc-Si) was evaluated by Raman spectroscopy. The nc-Si dot layers were fabricated by the H2 plasma treatment for the nucleation site formation followed by the SiH4 irradiation for the nc-Si growth. Post-oxidation annealing was also performed to improve the crystalline quality. After post-oxidation annealing for 5 or 10 min, the asymmetric broadening on the lower frequency sides in Raman spectra were obtained, which can be attributed to the phonon confinement effect in nc-Si. Furthermore we confirmed that hydrostatic stress of approximately 500 MPa was induced in nc-Si after post-oxidation annealing.

We evaluated the properties of crystalline defects in silicon substrate, and clarified the origin of small-angle grain boundaries. In order to eliminate the effects of grain boundaries, the ingot was fabricated by unidirectional solidification technique with seed crystal. In single-crystalline region, Σ3 twin boundaries and SiC precipitates were observed near the seed crystal. No obvious relationship between twin boundaries and precipitates was observed. These defect decreased once and the precipitations appeared again. The density of precipitates increased through the crystal growth procedure. These precipitates were consisted of Si, C, and N. After the precipitation density increased, the small-angle grain boundaries appeared and some precipitates were observed at the boundaries. We considered the precipitations consisted of light element impurities such as C and N were one of the major origins of the small-angle grain boundary generation.

Interactions between intra-grain defects and metal impurities in multicrystalline silicon (mc-Si) were evaluated. After metal contaminations, EBIC contrasts at > 1.5o SA-GBs were more enhanced than those at Ni/1000 oC > Ni/600 oC. These results might attribute to Fe atoms form deeper energy levels of recombination centers than Ni atoms and the gettering abilities at SA-GBs depend on the misorientation angles. Many dark spots were observed in EBIC images in the Ni/600 oC. Since the dark spots corresponded to the etch pits, the dark spots might be dislocations decorated with Ni. The gettering abilities of SA-GBs depended on the misorientaion angles, and the recombination properties at SA-GBs and dark spots, such as small defects after metal contamination were different by annealing temperatures and the types of metal impurities.

This paper describes structure evaluation of GexSbyTez (GST) film fabricated by chemical vapor deposition (CVD). We successfully established composition controlled GST CVD with smooth surface by applying appropriate deposition conditions. By increasing Ge flow rate or reducing substrate temperature, the average grain size was reduced and the film flatness was improved. As the results, we succeeded to obtain the extremely smooth surface, and also to fill a finite hole with conformal film deposition. All GexSbyTez films showed FCC or amorphous crystalline structures, both are utilized in the proposed phase change random access memory (PRAM), in spite of the wide range of composition control. We believe these CVD-GST films are useful for PRAM applications.