The influence of monovalent cation halide additives on the optical, excitonic, and electrical properties of CH3NH3PbI3 perovskite is reported. Monovalent cation halide with similar ionic radii to Pb2+, including Cu+, Na+, and Ag+, have... more
The influence of monovalent cation halide additives on the optical, excitonic, and electrical properties of CH3NH3PbI3 perovskite is reported. Monovalent cation halide with similar ionic radii to Pb2+, including Cu+, Na+, and Ag+, have been added to explore the possibility of doping. Significant reduction of sub-bandgap optical absorption and lower energetic disorder along with a shift in the Fermi level of the perovskite in the presence of these cations has been observed. The bulk hole mobility of the additive-based perovskites as estimated using the space charge limited current method exhibits an increase of up to an order of magnitude compared to the pristine perovskites with a significant decrease in the activation energy. Consequentially, enhancement in the photovoltaic parameters of additive-based solar cells is achieved. An increase in open circuit voltage for AgI (≈1.02 vs 0.95 V for the pristine) and photocurrent density for NaI- and CuBr-based solar cells (≈23 vs 21 mA cm−2 for the pristine) has been observed. This enhanced photovoltaic performance can be attributed to the formation of uniform and continuous perovskite film, better conversion, and loading of perovskite, as well as the enhancement in the bulk charge transport along with a minimization of disorder, pointing towards possible surface passivation.
PERC cells were fabricated using two different aluminum precursors for the Al2O3 rear surface passivation layer. TMA and non-pyrophoric DMAi based Al2O3 layers were implemented in p-type Cz-Si PERC for rear surface passivation. The Al2O3... more
PERC cells were fabricated using two different aluminum precursors for the Al2O3 rear surface passivation layer. TMA and non-pyrophoric DMAi based Al2O3 layers were implemented in p-type Cz-Si PERC for rear surface passivation. The Al2O3 layers deposition was performed by ALD, PEALD and PECVD. The best conversion efficiency was obtained for the cells using a 10 nm DMAi based Al2O3 layer, deposited by PECVD (20.1 %). The TMA-Al2O3 based PERC cells achieved nearly identical conversion efficiencies (max 20.0 %).
The transition potential and the repassivation potential of AISI type 316 stainless steel was investigated in the absence and the presence of 0.01 M thiosulfate in chloride containing media. The pencil electrode method was employed to... more
The transition potential and the repassivation potential of AISI type 316 stainless steel was investigated in the absence and the presence of 0.01 M thiosulfate in chloride containing media. The pencil electrode method was employed to explore the key factors affecting the pit transition potential and the repassivation potential in thiosulfate containing solution. Using this method the pit chemistry at various temperatures was also evaluated. A good correlation was found between the pitting potential and the pit transition potential at various temperatures. Moreover, there was a significant decrease in the repassivation potential by addition of 0.01 M thiosulfate. The results were in accordance with the theory suggesting that the chemistry of the pit governs the pit repassivation potential.
Surface defects caused during cutting and polishing in the fabrication of cad-mium zinc telluride (CdZnTe) nuclear detectors limit their spectral performance. Chemical treatments are often used to remove surface damages and defects. In... more
Surface defects caused during cutting and polishing in the fabrication of cad-mium zinc telluride (CdZnTe) nuclear detectors limit their spectral performance. Chemical treatments are often used to remove surface damages and defects. In this paper, we present the analysis of Te and TeO 2 species on the surfaces of CdZnTe nuclear detectors treated with hydrogen bromide and ammonium-based solutions. The CdZnTe wafers were chemo-mechanically polished in a mixture of hydrogen bromide in hydrogen peroxide and ethy-lene glycol, followed by a chemical passivation in a mixture of ammonium fluoride and hydrogen peroxide solution. X-ray photoelectron spectroscopy showed significant conversion of Te to TeO 2 , thus producing a more chemically stable surface. The resistivity of the CdZnTe samples is in the order of 10 10 ohms-cm. The current for a given applied voltage increased following the passivation and decreased after a 3-hour period. Results from spectral response measurements showed that the 59.5-keV gamma-peak of Am-241 was stable under the same channel for the surface treatment processes.
In the present study, surface mechanical attrition treatment (SMAT) and plasma nitriding were conducted on AISI 2205 steel. SMAT was effective in enhancing the surface hardness of the steel by about 80%. The influence of SMAT on the... more
In the present study, surface mechanical attrition treatment (SMAT) and plasma nitriding were conducted on AISI 2205 steel. SMAT was effective in enhancing the surface hardness of the steel by about 80%. The influence of SMAT on the corrosion behaviour of the steel was studied in a 3.5 wt-% NaCl solution. Due to the stable and thicker passive layer, improved corrosion resistance was observed for the SMATed steel. However, nitrogen diffusion during plasma nitriding was impeded by the improved passivation, especially for the lower duration (30 min) of chemical etching/cleaning (i.e. sputter cleaning in hydrogen plasma) of the specimen's surface. Furthermore, high chemical etching duration (120 min) resulted in improved surface hardness and nitriding kinetics.
The corrosion of the surfaces of metallic implants is a very aggressive process, which can cause inflammation and deposition of metal in the surrounding live tissue. Prevention of corrosion and improvement of the functional... more
The corrosion of the surfaces of metallic implants is a very aggressive process, which can cause inflammation and deposition of metal in the surrounding live tissue. Prevention of corrosion and improvement of the functional characteristics of different coatings for application on implant surfaces is essential. Niobium and tantalum anodic oxides of optimal thickness have enabled the manufacture of a new generation of bioengineering products displaying minimal corrosion.
Despite the predominance of single junction solar cells, both in research and commercial production, triode or transistor structure solar cells offer performance advantages on a range of substrate materials. This paper uses the... more
Despite the predominance of single junction solar cells, both in research and commercial production, triode or transistor structure solar cells offer performance advantages on a range of substrate materials. This paper uses the semiconductor device simulator PC1D to compare a single junction silicon solar cell with two silicon transistor structures, in order to quantify the expected performance increases, and to show how minority carrier diffusion length and wafer thickness influence these relative advantages.
To improve the performance of the polycrystalline thin film devices, it requires a delicate control of its grain structures. As one of the most promising candidates among current thin film photovoltaic techniques, the organic/inorganic... more
To improve the performance of the polycrystalline thin film devices, it requires a delicate control of its grain structures. As one of the most promising candidates among current thin film photovoltaic techniques, the organic/inorganic hybrid perovskites generally inherit polycrystalline nature and exhibit compositional/structural dependence in regard to their optoelectronic properties. Here, we demonstrate a controllable passivation technique for perovskite films, which enables their compositional change, and allows substantial enhancement in corresponding device performance. By releasing the organic species during annealing, PbI2 phase is presented in perovskite grain boundaries and at the relevant interfaces. The consequent passivation effects and underlying mechanisms are investigated with complementary characterizations, including scanning electron microscopy (SEM), X-ray diffraction (XRD), time-resolved photoluminescence decay (TRPL), scanning Kelvin probe microscopy (SKPM), a...
Infrared spectroscopy is used to compare the Si/SiO2 interfaces created by thermal oxidation of a standard Si(100) substrate and of an ordered, (1x1) Si(100) substrate. The thermal oxides (approximately 25 Angstrom) examined in this study... more
Infrared spectroscopy is used to compare the Si/SiO2 interfaces created by thermal oxidation of a standard Si(100) substrate and of an ordered, (1x1) Si(100) substrate. The thermal oxides (approximately 25 Angstrom) examined in this study are etched in dilute hydrofluoric acid and the resulting films analyzed spectroscopically. The behavior of the dominant optical phonon modes as a function of film thickness provides strong evidence that the ordered Si(100) substrate provides a template for an Si/SiO2 interface with a higher degree of homogeneity in the Si-O bonding environment of the intervening substoichiometric SiOx layer than does the standard Si(100) substrate. (C) 2004
In situ photoluminescence combined with optical emission spectroscopy, effective carrier lifetime, radio-frequency (RF) and self-bias potential measurements has been used to study plasma-induced damage at the a-Si:H/c-Si interface.... more
In situ photoluminescence combined with optical emission spectroscopy, effective carrier lifetime, radio-frequency (RF) and self-bias potential measurements has been used to study plasma-induced damage at the a-Si:H/c-Si interface. Passivated crystalline silicon wafers were exposed to Ar, H2, and Ar-H2 RF plasmas using the same value of RF power and pressure in the range of 80–100 mTorr. The substrate temperature during the plasma exposure was room temperature or 200 C. It is found that Ar-H2 plasma has the most detrimental effect on the photoluminescence intensity/effective carrier lifetime which correlates well with its UV spectrum. After plasma exposure, surface passivation can be recovered by thermal annealing—an effect similar to that observed in the case of light-induced degradation of a-Si:H.
To improve the performance of the polycrystalline thin film devices, it requires a delicate control of its grain structures. As one of the most promising candidates among current thin film photovoltaic techniques, the organic/inorganic... more
To improve the performance of the polycrystalline thin film devices, it requires a delicate control of its grain structures. As one of the most promising candidates among current thin film photovoltaic techniques, the organic/inorganic hybrid perovskites generally inherit polycrystalline nature and exhibit compositional/structural dependence in regard to their optoelectronic properties. Here, we demonstrate a controllable passivation technique for perovskite films, which enables their compositional change, and allows substantial enhancement in corresponding device performance. By releasing the organic species during annealing, PbI2 phase is presented in perovskite grain boundaries and at the relevant interfaces. The consequent passivation effects and underlying mechanisms are investigated with complementary characterizations, including scanning electron microscopy (SEM), X-ray diffraction (XRD), time-resolved photoluminescence decay (TRPL), scanning Kelvin probe microscopy (SKPM), a...
The goal of the present investigation is to reduce the stress, strain, and defects of porous silicon through a pas-sivation process. We have investigated different layers of porous silicon (PSL) which were intentionally doped with... more
The goal of the present investigation is to reduce the stress, strain, and defects of porous silicon through a pas-sivation process. We have investigated different layers of porous silicon (PSL) which were intentionally doped with sa-marium (Sm) by the electrochemical deposition. The used precursors were samarium oxides (Sm 2 O 3) 0.05 M mixed with sulfuric acid (H 2 SO 4) 0.05 M. The influence of samarium on the distribution of oxygen was studied by Fourier transform infrared spectroscopy (FTIR). Indeed, the glancing incidence X-ray diffraction proves the degree of structural order in PS and the presence of these complex metals (Sm) on its surface. The dispersion of the Sm metals on the PS surface (Sm/PSLs) exhibited better performances for the treated wafers in regard to the untreated ones. That means, we obtained a noteworthy increase in the effective minority carrier lifetime τ eff and an apparent enhancement in photoluminescence (PL) intensity. Particularly, the chief goal of the current study is to clarify that the large enhancement of the electronic quality of the wafers is related to the presence of Sm.
""Three different HF:alcohol solutions are investigated to etch native Si0 2 and passivate Si(100) surfaces with H which can the be desorbed at low temperature (T < 600'C). The resulting passivated Si(100) surfaces are compared using as a... more
""Three different HF:alcohol solutions are investigated to etch native Si0 2 and passivate Si(100) surfaces with H which can the be desorbed at low temperature (T < 600'C). The resulting passivated Si(100) surfaces are compared using as a reference Si(100) passivated by a standard aqueous HF: solution (1:98 parts of HF: H2 0). After a modified RCA cleaning, Si(100) etched by HF:Methanol, HF:IPA, or HF:Ethanol, is characterized by Ion Beam Analysis (IBA), Tapping Mode Atomic Force Microscope (TMAFM), and Fourier Transform Infrared Spectroscopy (FTIR). The absolute coverage of 0 and C is measured by nuclear reaction analysis (NRA) combined with ion channeling at 3.05 MeV for 0 and 4.265 MeV for C. Hydrogen is measured via the elastic recoil detection (ERD) of 4He2+at 2.8 MeV.
Compared to aqueous HF, HF:alcohol passivates Si(100) leaving a lower 0 residue by an average factor of 0.62 and a similar C residue. H coverage is higher by an average factor of 1.43. Surface coverages are found to be reproducible in average by 1.4 x 1014 atoms/cm2 for C, and by 1.25 x 1014 atoms/cm2 for 0 when measured by IBA on samples identically processed. H coverage is reproducible within 5.5% when measured by ERD.
Selective area analysis by TMAFM shows that an increasing number of particulates is responsible for the apparent increase in root-mean -square (nns) surface roughness when the rms is measured over a whole image. Taking this effect into account, all passivated surfaces exhibit similar roughness when compared to the original Si(100) surface with little difference between
alcohols and with the reference aqueous HF solution. FTIR in the attenuation total reflection (ATR) mode detected SiHx species mostly as a
dihydride. Both IBA and FTIR detected significant levels of oxygen on surfaces passivated HF in alcohol and aqueous HF. This indicates that while Si(100) exhibits more H when passivated with HF in alcohol and can be desorbed at lower temperature than when treated with aqueous HF, H is
not bonded to Si only but likely bonds into a more complex surface termination, such as SiOH.""
Using ion beam modification, films composed of synthesized ‘‘interphases’’ of ordered silica on OH-passivated (1 X 1) Si(100) underwent surface electro-chemical changes quantified by surface free energy via Sessile drop method and... more
Using ion beam modification, films composed of synthesized
‘‘interphases’’ of ordered silica on OH-passivated (1 X 1) Si(100) underwent surface electro-chemical changes quantified by surface free energy via Sessile drop method and contact angle analysis using Young’s equation and Van Oss theory. IBMM caused the surface free energies initially ranging from 26.0 mJ/m2 to 57.3 mJ/m2 to converge to 43.1–45.4 mJ/m2 for various passivated and as-received wafer samples alike. Although TMAFM also identified topographic changes, these changes did not correlate to the change of surface free energies. Ion beam modification of the ordered silica film on Si(100) surface is analyzed using 3.045 MeV 16O(a, a)16O nuclear resonance scattering (NRS) in conjunction with channeling in (1 1 1) direction, which demonstrated the convergence of the partially ordered oxygen to amorphous at about 55 microCoulombs/mm2 He++ flux. Additionally, Si surface peak channeling in (1 0 0) and (1 1 1) directions also experienced an uptrend in areal density as incident ion flux increased, while the rotating random Si signal height remains stable, showing a disruption in the surface order during IBMM.
We use ion beam analysis to probe the structure and interface of ultrathin thermal oxide films grown on (1x1) Si(100) surfaces prepared using the Herbots-Atluri [U.S. patent No. 6,613,677 (Sept. 2, 2003)] wet chemical clean. We discover... more
We use ion beam analysis to probe the structure and interface of ultrathin thermal oxide films grown on (1x1) Si(100) surfaces prepared using the Herbots-Atluri [U.S. patent No. 6,613,677 (Sept. 2, 2003)] wet chemical clean. We discover that these oxide layers are structurally registered with the substrate lattice with no interfacial structural disorder. Registry of Si atoms is most pronounced along < 111 > directions relative to the Si substrate, consistent with a beta-cristobalite epitaxial phase. This structurally registered phase transitions to an amorphous structure approximately 2 nm from the interface.(c) 2006
Metal oxide thin films, suitable for use on solar energy converters and photocatalitic applications, have been characterized on-line by ellipsometric monitoring system. Ellipsometry is a powerful and non-invasive technique of film... more
Metal oxide thin films, suitable for use on solar energy converters and photocatalitic applications, have been characterized on-line by ellipsometric monitoring system. Ellipsometry is a powerful and non-invasive technique of film analysis but it is indirect tool. The most interesting parameters such as film thickness and complex refractive indices can be determined only by computer sample modelling. The complex reflection coefficients obtained from model calculation were compared with ellipsometric measurements. We discuss composition of multilayer film structure using various models and fittings method. The implementation of effective medium approximation procedure enables to interpret multilayer oxides structure formation during passivation process. It is shown that an accurate model fitting was obtained using Levenberg-Marquardt optimization algorithm and multidimensional mean square error.
Biosafety of AZ31B magnesium (Mg) alloy and the effect of its degradation products on tissues, organs, and whole systems are highly needed to be evaluated before clinical application. This study serves a wide variety of safety evaluations... more
Biosafety of AZ31B magnesium (Mg) alloy and the effect of its degradation products on tissues, organs, and whole systems are highly needed to be evaluated before clinical application. This study serves a wide variety of safety evaluations of biodegradable AZ31B alloy on nerve cells. As a result of this in vitro study, the maximum aluminum (Al) ion and Mg ion concentrations in the medium were estimated to be 22 μmol/L and 2.75 mmol/L, respectively, during degradation. In addition, the
In this paper zeolite Beta was synthesized and characterized by XRD, ATG, ATD, XRF and SEM. Subsequently various modifications were made using a surface passivation process in liquid phase with tetraethylorthosilicate (TEOS), using two... more
In this paper zeolite Beta was synthesized and characterized by XRD, ATG, ATD, XRF and SEM. Subsequently various modifications were made using a surface passivation process in liquid phase with tetraethylorthosilicate (TEOS), using two loads of TEOS and three passivation cycles, in order to obtain six catalysts. These materials were characterized by NH3-TPD and tested in tolune disproportionation reaction, under different conditions of pressure and temperature. As modification cycles were increased for each catalyst, there was a change in the acidity of the solids, mainly due to deposition of an inert layer of silica on the external surface. These results were confirmed with the improvement in para-selectivity and decreasing in conversion. Despite zeolite Beta is a large pore zeolite, an improvement of the para-selectivity was obtained, achieving almost stable values for the entire range of temperature and pressure conditions.
We have investigated the influence of solvents on the quality of hexadecanethiol (HDT) self-assembled monolayers (SAM) formed on GaAs (0 0 1) in chloroform, ethanol and ethanol/water 1:1 characterized by their increasing dielectric... more
We have investigated the influence of solvents on the quality of hexadecanethiol (HDT) self-assembled monolayers (SAM) formed on GaAs (0 0 1) in chloroform, ethanol and ethanol/water 1:1 characterized by their increasing dielectric constants from 4.8 (chloroform) to 24.5 (ethanol) and water (80.1). Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) data show that the incubation in ethanol/water 1:1 solution creates conditions favouring inter-molecular interaction leading to the formation of an outstanding quality HDT SAM on GaAs (0 0 1). Incubation in low-dielectric constant solvents is not offering advantageous conditions for growing HDT SAM on GaAs. The chloroform environment, while weakening the thiol–thiol interaction, induces the oxidation of the GaAs surface and, in particular, formation of Ga2O3. This reduces the concentration of surface defects responsible for non radiative recombination and leads to an enhanced photoluminescence emission, despite the fact that HDT SAM formed in chloroform are highly disordered, exhibiting the worst chemical passivation among the investigated samples.
M anaging trap states and understanding their role in ultrafast charge-carrier dynamics, particularly at surface and interfaces, remains a major bottleneck preventing further advancements and commercial exploitation of nanowire (NW)-based... more
M anaging trap states and understanding their role in ultrafast charge-carrier dynamics, particularly at surface and interfaces, remains a major bottleneck preventing further advancements and commercial exploitation of nanowire (NW)-based devices. A key challenge is to selectively map such ultrafast dynamical processes on the surfaces of NWs, a capability so far out of reach of time-resolved laser techniques. Selective mapping of surface dynamics in real space and time can only be achieved by applying four-dimensional scanning ultrafast electron microscopy (4D S-UEM). Charge carrier dynamics are spatially and temporally visualized on the surface of InGaN NW arrays before and after surface passivation with octadecylthiol (ODT). The time-resolved secondary electron images clearly demonstrate that carrier recombination on the NW surface is signifi cantly slowed down after ODT treatment. This observation is fully supported by enhancement of the performance of the light emitting device. Direct observation of surface dynamics provides a profound understanding of the photophysical mechanisms on materials’ surfaces and enables the formulation of effective surface trap state management strategies for the next generation of high-performance NW-based optoelectronic devices.
Abstract: The microstructure and stoichiometry of nitrides formed by direct low-energy ion beam nitridation has been investigated as a function of ion energy and substrate temperature for Si(100) and SiGe/Si(100) films. Cross-sectional... more
Abstract: The microstructure and stoichiometry of nitrides formed by direct low-energy ion beam nitridation has been investigated as a function of ion energy and substrate temperature for Si(100) and SiGe/Si(100) films. Cross-sectional transmission electron microscopy, Rutherford backscattering spectroscopy combined with ion channeling and in situ x-ray photoelectron spectroscopy were used. It was established that a substrate temperature of 700 K produces a homogeneous amorphous nitride layer, whereas lower substrate temperatures decrease the incorporation of nitrogen in the film, while causing the formation of a nitrogen-poor amorphous layer beneath the nitride film. The N-to-Si or N-to-(Si + Ge) atomic ratio is found be close to 1.33 at 1 keV and decreases with ion energy. Effects due to chemically enhanced physical sputtering of germanium are observed.
Biosafety of AZ31B magnesium (Mg) alloy and the effect of its degradation products on tissues, organs, and whole systems are highly needed to be evaluated before clinical application. This study serves a wide variety of safety evaluations... more
Biosafety of AZ31B magnesium (Mg) alloy and the effect of its degradation products on tissues, organs, and whole systems are highly needed to be evaluated before clinical application. This study serves a wide variety of safety evaluations of biodegradable AZ31B alloy on nerve cells. As a result of this in vitro study, the maximum aluminum (Al) ion and Mg ion concentrations in the medium were estimated to be 22 μmol/L and 2.75 mmol/L, respectively, during degradation. In addition, the corresponding cell mortality was observed to be 36% and lower than 5% according to the resistance curves of the cell to Mg and Al ions. Furthermore, the maximum Al ion and Mg ion concentrations in serum and cerebrospinal fluid were detected to be 26.1 μmol/L and 1.2 mmol/L, respectively, for 5 months implantation. Combining the result of in vivo dialysis with the result of ion tolerance assay experiments, the actual death rate of nerve cells is estimated between 4 and 10% in vivo, which is lower than the result of in vitro cytotoxicity evaluation. Moreover, no psychomotor disability during clinical studies is observed. Consequently, stent made of AZ31B alloy with surface treatment is feasible for carotid artery stenosis, and it is safe in terms of cell viability on the nervous system.
An analytical model for the position-dependent collection probability in uniformly doped one-dimensional layers with abrupt compositional and bandgap changes is presented. The collection probability is derived from coupled system of... more
An analytical model for the position-dependent collection probability in uniformly doped one-dimensional layers with abrupt compositional and bandgap changes is presented. The collection probability is derived from coupled system of diffusion equations for lowlevel injection of photo-generated minority carriers in a stack of isotype heterolayers. Collection probability maintained continuity across isotype heterojunctions despite discontinuities of excess minority carrier concentration. An estimate for window and BSF passivation showed that the effective surface recombination velocity exponentially depended on the energygap difference, and linearly depended on increased doping, reduced mobility and increased thickness of sub-diffusion length passivation layers. Analytical expressions for the photo-generated current, and the internal quantum efficiency from each heterolayer were developed, and applied to the analysis of reported spectral response of a dual junction GaInP/GaAs tandem solar cell. Calculated internal quantum efficiencies closely matched reported experimental results, with the exception of sub-band absorption due to sub-bandgap deficiencies in the optical models and photon recycling. Calculated spectral response showed that upper AlInP 2 window, quasi-neutral emitter, and SCR layers dominated collection of photo-generated carriers in the top GaInP 2 cell, whereas, the base dominated collection of photo-generated carriers in the bottom GaAs cell. Results show that augmenting Hovel's three layers (emitter, SCR, and base) analysis with the response from the top window layer should be sufficient to capture the spectral response of solar cells with thin passivation layers.
ABSTRACTThe electronic properties of diamond, e.g. a high band-gap and high carrier mobilities, together with material properties such as a very high thermal conductivity, chemical inertness and a high radiation resistance makes diamond a... more
ABSTRACTThe electronic properties of diamond, e.g. a high band-gap and high carrier mobilities, together with material properties such as a very high thermal conductivity, chemical inertness and a high radiation resistance makes diamond a unique material for many extreme electronic applications out of reach for silicon devices. This includes, e.g. microwave power devices, power devices and high temperature electronics. It is important to have an effective passivation of the surface of such devices since the passivation determines the ability of the device to withstand high surface electric fields. In addition, the passivation is used to control the surface charge which can strongly influence the electric field in the bulk of the device. It is possible to measure sample parameters such as electron and hole drift mobilities, charge carrier lifetimes or saturation velocities using Time-of-flight (ToF) method. The ToF technique has also been adapted for probing the electric field distri...
ABSTRACT In this work, quartz crystal microbalance (QCM) crystal surfaces were analyzed in order to study the behavior of protein attachment on fouling substrates. In this context, covalent and noncovalent immobilization of different... more
Recently, Cu(In,Ga)Se2 (CIGS) solar cells have achieved 21% world-record efficiency, partly due to the introduction of a postdeposition potassium treatment to improve the front interface of CIGS absorber layers. However, as... more
Recently, Cu(In,Ga)Se2 (CIGS) solar cells have achieved 21% world-record efficiency, partly due to the introduction of a postdeposition potassium treatment to improve the front interface of CIGS absorber layers. However, as high-efficiency CIGS solar cells essentially require long diffusion lengths, the highly recombinative rear of these devices also deserves attention. In this paper, an Al2O3 rear surface passivation layer with nanosized local point contacts is studied to reduce recombination at the standard Mo/CIGS rear interface. First, passivation layers with well-controlled grids of nanosized point openings are established by use of electron beam lithography. Next, rear-passivated CIGS solar cells with 240-nm-thick absorber layers are fabricated as study devices. These cells show an increase in open-circuit voltage (+57 mV), short-circuit current (+3.8 mA/cm2), and fill factor [9.5% (abs.)], compared with corresponding unpassivated reference cells, mainly due to improvements in rear surface passivation and rear internal reflection. Finally, solar cell capacitance simulator (SCAPS) modeling is used to calculate the effect of reduced back contact recombination on high-efficiency solar cells with standard absorber layer thickness. The modeling shows that up to 50-mV increase in open-circuit voltage is anticipated.
The electronic properties of diamond, e.g. a high band-gap and high carrier mobilities, together with material properties such as a very high thermal conductivity, chemical inertness and a high radiation resistance makes diamond a unique... more
The electronic properties of diamond, e.g. a high band-gap and high carrier mobilities, together with material properties such as a very high thermal conductivity, chemical inertness and a high radiation resistance makes diamond a unique material for many extreme electronic applications out of reach for silicon devices. This includes, e.g. microwave power devices, power devices and high temperature electronics. It is important to have an effective passivation of the surface of such devices since the passivation determines the ability of the device to withstand high surface electric fields. In addition, the passivation is used to control the surface charge which can strongly influence the electric field in the bulk of the device. It is possible to measure sample parameters such as electron and hole drift mobilities, charge carrier lifetimes or saturation velocities using Time-of-flight (ToF) method. The ToF technique has also been adapted for probing the electric field distribution and the distribution of trapped charge. In this paper we present new data from lateral ToF studies of high-purity single crystalline diamond with different surface passivations. Silicon oxide and silicon nitride are used as passivation layers in the current study. The effect of the passivation on charge transport is studied, and the results of different passivation materials are compared experimentally.
Epitaxial growth requires an initial surface that is ordered and as free as possible of contaminants such as C, 0, or metallic impurities. Wet chemical etching of Si( 111) wafers by a solution of HF in alcohol after a modified RCA clean,... more
Epitaxial growth requires an initial surface that is ordered and as free as possible of contaminants such as C, 0, or
metallic impurities. Wet chemical etching of Si( 111) wafers by a solution of HF in alcohol after a modified RCA clean, has
been shown to produce (1 X 1) H-terminated hydrophobic Si surfaces that are ordered at room temperature and can be
desorbed at 200°C in UHV. Less is known about a similar treatment on Si(lO0) wafers, more commonly used in
semiconductor technology. However, high temperature (T> 800°C) thermal desorption of the native oxide on Si(lO0) is
known to induce detrimental effects such as surface roughness, precipitation and dopant segregation. Therefore, this study is
motivated by the development of a low-temperature (T < 600°C) surface cleaning method for Sit 100). RBS combined with
ion channeling and nuclear reaction analysis is conducted to measure the coverage of C, 0, and H as well as the residual
disorder at the surface at different steps of wet chemical cleaning prior to low temperature desorption. Hydrogen is detected
by the forward elastic recoil of H by 4He2+ at 2.8 MeV. 0 and C are detected by nuclear reaction analysis (NRA) at 3.05
and 4.265 MeV, respectively, in combination with ion channeling along the Si( 111) direction to increase the detection
sensitivity for C and 0 as well as to measure the Si surface peak to correlate it to surface disorder. Atomic force microscopy
of these surfaces has shown different degrees of roughness in addition to defect formation and is correlated to the ion beam
analysis results. Our results indicate a strong dependence of final H-passivation on the pretreatment of the Si surfaces before
the final dip in the HE/alcohol solution.
Atomic-layer-deposited (ALD) aluminum oxide (Al2O3) has recently demonstrated an excellent surface passivation for both n- and p-type c-Si solar cells thanks to the presence of high negative fixed charges (Qf ∼ 1012−1013 cm−2) in... more
Atomic-layer-deposited (ALD) aluminum oxide (Al2O3) has recently demonstrated an excellent surface passivation for both n- and p-type c-Si solar cells thanks to the presence of high negative fixed charges (Qf ∼ 1012−1013 cm−2) in combination with a low density of interface states (Dit). This paper in- vestigates the passivation quality of thin (15 nm) Al2O3 films deposited by two different techniques: plasma- enhanced atomic layer deposition (PE-ALD) and Thermal atomic layer deposition (T -ALD). Other dielec- tric materials taken into account for comparison include: thermally-grown silicon dioxide (SiO2) (20 nm), SiO2 (20 nm) deposited by plasma-enhanced chemical vapour deposition (PECVD) and hydrogenated amorphous silicon nitride (a-SiNx:H) (20 nm) also deposited by PECVD. With the above-mentioned di- electric layers, Metal Insulator Semiconductor (MIS) capacitors were fabricated for Qf and Dit extraction through Capacitance-Voltage-Conductance (C-V-G) measurements. In addition, lifetime measurements were carried out to evaluate the effective surface recombination velocity (SRV). The influence of extracted C-V-G parameters (Qf,Dit) on the injection dependent lifetime measurements τ(Δn), and the dominant passivation mechanism involved have been discussed. Furthermore we have also studied the influence of the SiO2 interfacial layer thickness between the Al2O3 and silicon surface on the field-effect passivation mechanism. It is shown that the field effect passivation in accumulation mode is more predominant when compared to surface defect passivation.
