Effect Of Chemical Passivation Research Articles

Effects of CuAlO2 on the heterojunction interface and performance of Cu2ZnSn(S,Se)4 thin-film solar cells

Carrier transportation and efficiency of Cu2ZnSn(S,Se)4 (CZTSSe) solar cells are seriously inhibited due to heterojunction interface (HEI) recombination. Herein, we firstly propose a novel HEI doping strategy to address HEI recombination issue by introducing Cu-poor (& Al-rich) CuAlO2 (CAO). Our results indicate that interfacial elements interdiffusion took place between Cu from absorber and Al from CAO during selenization. Then, occupation of Al on the Cu site leads to the absorber shallow bulk inversion from p to n-type, and thereout constructs a desirable homogeneous field passivation (HFP) for HEI. It has not only a superior photo-induced charge carrier transportation function and penalizes the probability of electron-hole recombination but also leads to the superior carrier separation capacity via enlarging depletion region. In addition, CAO itself can bring about a chemical passivation effect owing to its high resistivity. As a result, synergistic passivation effect combining common chemical passivation with novel HFP was realized. Finally, we achieved 9.34% efficiency kesterite device involving chemical and field passivation effects simultaneously despite the relatively not top efficiency. In this regard, HEI doping engineering induced with characteristic Cu-poor (& Al-rich) material for absorber shallow bulk inversion and appreciable passivation effect achieved here shine a new light on the development of kesterite device.

Dual Optimization of Back Electrode Interface and Bulk via the Synergistic Passivation Effect of Niobium Pentoxide Enables Efficient Kesterite Solar Cells

As compared to the predecessor Cu(In,Ga)Se2 device, the current efficiency of kesterite Cu2ZnSn(S,Se)4 (CZTSSe) solar cells is still much lower mainly due to the known carriers recombination issue within interface and absorber bulk. In contrast to the majority of researches concerning recombination issues that focus on either single absorber bulk or interface passivation strategy, this study is pioneering in constructing synergistic passivation effects (SPE) to address the bulk and interface recombination issue simultaneously. By introducing a novel niobium pentoxide passivation layer into the back electrode interface (BEI), it is identified that SPE can be constructed due to Nb (& O) diffusion from Nb2O5 layer to absorber bulk and BEI during high‐temperature selenization. The chemical passivation effect is fulfilled via the intrinsic high resistance characteristic of Nb2O5 layer, and also through the NbOx passivation aiming to absorber bulk benefited from Nb (& O) diffusion. Meanwhile, the occupations of Nb (& O) on the Mo (& Se) sites induce a conduction type inversion in MoSe2 interfacial layer and create a preferable interface p+‐Mo(Se,O)2:Nb/CZTSSe, achieving an interfacial field passivation effect. Ultimately, the promoted absorber quality and improved charge carrier transportation from SPE contribute to the boost of device performance beyond 10% efficiency.

Effect of Chemical Passivation of GaAs(001) Surface on Anisotropy and Orientation of Gold Nanoclusters Formed on It and Their Plasmons

Effect of Chemical Passivation of GaAs(001) Surface on Anisotropy and Orientation of Gold Nanoclusters Formed on It and Their Plasmons

Dual‐Phase Stabilized Perovskite Nanowires for Reduced Defects and Longer Carrier Lifetime

Abstract1D perovskite materials are of significant interest to build a new class of nanostructures for electronic and optoelectronic applications. However, the study of colloidal perovskite nanowires (PNWs) lags far behind those of other established perovskite materials such as perovskite quantum dots and perovskite thin films. Herein, a dual‐phase passivation strategy to synthesize all‐inorganic PNWs with minimized surface defects is reported. The local phase transition from CsPbBr3 to CsPb2Br5 in PNWs increases the photoluminescence quantum yield, carrier lifetime, and water‐resistivity, owing to the energetic and chemical passivation effect. In addition, these dual‐phase PNWs are employed as an interfacial layer in perovskite solar cells (PSCs). The enhanced surface passivation results in an efficient carrier transfer in PSCs, which is a critical enabler to increase the power conversion efficiency (PCE) to 22.87%, while the device without PNWs exhibits a PCE of 20.74%. The proposed strategy provides a surface passivation platform in 1D perovskites, which can lead to the development of novel nanostructures for future optoelectronic devices.

Zwitterionic ionic liquid synergistically induces interfacial dipole formation and traps state passivation for high-performance perovskite solar cells

Defects at the interface and grain boundaries of perovskite solar cells (PSCs) will result in severe non-radiative recombination and open-circuit voltage (Voc) loss. Herein, we reported a zwitterionic ionic liquid imidazolium tetrafluoroborate (IMBF4) to passivate the defects at tin dioxide (SnO2)/perovskite interface. The results showed that the electron-rich nitrogen atom contained IM+ could diffuse into the buried perovskite to exhibit a strong chemical passivation effect on the organic vacancy defect by interacting with uncoordinated Pb2+. The F– in BF4- has a strong coordination effect with Pb2+in perovskite and Sn2+ in SnO2 synchronously to fill the anion vacancy defect. Also, the BF4- anions could help to form an interface dipole layer to increase the charge transfer rate and reduce the work function. The IMBF4 modified device could achieve an efficiency enhancement from 20.18% to 23.05% by vacuum flash-assisted solution-processed, with the increased Voc from 1.09 V to 1.15 V. The unencapsulated IMBF4 modified device could maintain 93% of the initial efficiency after ageing for 2000 h under ambient conditions by the ISOS-D-1 stability-testing protocols. This work emphasizes the importance of multifunctional additives in passivating defects and improving interface contact for achieving efficient and stable perovskite solar cells.

XXVI International Symposium Nanophysics and Nanoelectronics", Nizhny Novgorod, March 14-March 17, 2022 Effect of chemical passivation of GaAs(001) surface on anisotropy and orientation of gold nanoclusters formed on it and their plasmons

The principal role of chemical passivation of GaAs surface in the formation on it of oriented anisotropic nanoclusters of gold is discussed. The nanoclusters are fabricated by thermal annealing of a gold film deposited onto GaAs(001) surface passivated as a preliminary by a monolayer of nitrogen or sulfur atoms. These atoms, bonded chemically to gallium atoms of the crystal surface, form a crystal lattice and prevent the chemical interaction of Au with GaAs. As a result of annealing, the arrays of anisotropic (elongated) nanoclusters of chemically pure Au oriented preferably in crystal [110] direction are formed on passivated GaAs(001) surface. The presence of strong anisotropy and orientation of Au clusters on passivated GaAs surfaces is established by the methods of probe diagnostics and of optical reflectance anisotropy spectroscopy and polarized reflection spectroscopy. Using an optical model of plasmonic polarizability of elongated Au spheroids, it is shown that the spectral features observed in polarized reflection originate from anisotropic plasmons of Au nanoclusters polarized mainly in direction [110] of crystal. Keywords: semiconductor surface, nitride passivation, gold nanoclusters, anisotropic plasmons, polarized reflectance.

Оптические и электронные свойства пассивированных поверхностей InP(001)

The effect of chemical passivation in solutions of ammonium sulfide (NH4)2S on the optical and electronic properties of the n-InP (001) surface has been studied. It has been shown that treatment in a 4% aqueous solution of (NH4)2S leads to a decrease of surface band bending and localized charges in near-surface region in the 2 times. Processing in a 4% alcoholic solution of (NH4)2S leads to a decrease in these parameters in 3 times, and moreover, the barrier photovoltage and also reduces in three times.

Design and optimization of passivation layers and emitter layers in silicon heterojunction solar cells

<sec>Silicon heterojunction (SHJ) solar cells have attracted much attention in the international photovoltaic market due to their high efficiencies and low costs. The quality of amorphous silicon/crystalline silicon (a-Si:H/c-Si) interfaces of SHJ solar cells has a key influence on the device performance. Therefore, the carrier recombination rate of a-Si:H/c-Si interface needs to be effectively controlled. In addition, as the important component of SHJ solar cells, the p-type emitter must meet the requirements for high conductivity, high light transmittance, and energy band matching with c-Si. The research contents and the relevant achievements of this paper include the following aspects. </sec><sec>Firstly, in order to reduce the surface defects and realize the energy band alignment of a-Si:H/c-Si interface, the effect of passivation layer on passivation effect is studied. An ultra-thin buffer layer deposited by a low power and a high hydrogen dilution ratio is inserted between the conventional passivation layer and c-Si to improve the passivation effect and broaden the process window of passivation layer. The effects of the buffer layer thickness and hydrogen dilution ratio on passivation quality are further studied, and the best experimental conditions of buffer layer are obtained. The experimental results show that the sample with double-layered passivation layer is more stable than the conventional passivation layer. The minority carrier lifetime of the sample with single conventional passivation layer is 3.8 ms and the <i>iV</i><sub>OC</sub> is 712 mV, while the minority carrier lifetime of the sample with double-layered passivation layer is 4.197 ms and the <i>iV</i><sub>OC</sub> is 726 mV.</sec><sec>Secondly, for the p-type emitters of silicon heterojunction solar cells, the effects of doping level on the photoelectric properties of p-type hydrogenated nanocrystalline silicon (nc-Si:H) thin films are studied. On this basis, the p<sup>++</sup>-nc-Si:H/p-nc-Si:H double-layer emitter with wide band gap and high conductivity is designed and fabricated. By analyzing the optical and electrical properties of different emitters, it is found that p-nc-Si:H has good electrical and optical properties. Owing to the high doping efficiency of nc-Si, a small amount of doping can obtain high conductivity. Lightly doped p-nc-Si:H provides a better contact with the passivation layer, while heavily doped p<sup>++</sup>-nc-Si:H can not only provide enough built-in electric field, but also improve the contact characteristics of p/ITO, thus enhancing the output characteristics of the cell. At the same time, the deposition of p-nc-Si:H layer with high hydrogen dilution ratio can also implement the hydrogen plasma treatment on the passivation layer, the reduction of the dangling bonds on the surface of the c-Si, the enhancement of the chemical passivation effect, and thus improving the open circuit voltage of the cell. </sec><sec>Finally, a silicon heterojunction solar cell with an efficiency of 20.96% is obtained based on the commercial czochralski silicon wafer, with an open circuit voltage of 710 mV, a short circuit current density of 39.88 mA/cm<sup>2</sup> and filling factor of 74.02%.</sec>

Chemical passivation of the perovskite layer and its real-time effect on the device performance in back-contact perovskite solar cells

The back-contact architecture for perovskite solar cells (PSCs) offers the possibility of positioning both electrodes on one side of the absorber layer and shining light directly on the perovskite photoactive layer. This helps us to avoid the occurrence of transmission losses caused by the charge collecting transparent conductive oxide electrode in the conventional sandwich structure for PSCs. The back-contact device architecture is also useful for conducting fundamental studies as it has an exposed photoactive area, permitting in situ measurements on the effects of chemical treatment, passivation, and annealing. A successful application of back-contact PSCs in studying the effect of chemical passivation of the perovskite photo-absorber layer trap states with pyridine and its influence on the device performance have been studied. The real-time effect of pyridine vapor treatment on the device performance is visualized by monitoring the maximum power output of the devices under operation conditions. The device performance enhancement by ∼12% owing to the surface passivating effect of pyridine is demonstrated.

Effect of chemical passivation on corrosion behavior and ion release of a commercial chromium-cobalt alloy.

Background. Corrosion resistance and ion release of alloys play a crucial role in biomedical applications. The present study aimed to investigate an increase in corrosion resistance and reduction in ion release in a commercial Co-Cr-Mo alloy by the chemical passivation method. Methods. Based on ADA97, 20 samples of Flexicast alloy were cast, surface-polished, and electrolytically passivated at room temperature for 24 h in a sodium sulfate solution. Corrosion and ion release of the alloys before and after passivation were studied in normal saline solution. Corrosion resistance and the ion release rates were measured by the weight loss method and atomic absorption spectroscopy, respectively, before and after passivation after 1, 2, 3, and 4 weeks. The surface morphology of the samples was examined using scanning electron microscopy (SEM). The results were analyzed with Kruskal-Wallis and Mann-Whitney tests using SPSS 20 at a significance level of <0.05. Results. The corrosion rate in the passivated samples was significantly lower than the non-passivated samples at the intervals (1, 2, 3, and 4 weeks) (P<0.05). The passivation of the alloy significantly reduced Co and Cr ion release in the first and fourth weeks, and in the first, second, and fourth weeks, respectively (P<0.05). SEM images revealed localized pitting associated with the corrosion, which was less significant in passivated samples. Conclusion. Chemical passivation of the CR-Co alloy significantly reduced corrosion and ionic release of Cr and Co over time.

Passivation Mechanisms of Atomic Layer-deposited AlOx Films and AlOx/SiOx Stack

A new passivation layer of AlOx/SiOx were prepared, in which 80 nm SiOx was prepared by spin-coating perhydropolysilazane (PHPS) and annealed at 450°C. In order to compare the passivation effect of single AlOx layers and the SiOx/AlOx stack on silicon surface, the fixed charge (Qf) in the passivated layers and chemical passivation effect were obtained by corona charge method. Fourier transform infrared spectroscopy (FTIR) and Time-of-flight secondary ion mass spectrometry (TOF-SIMS) was used to investigate the Si-H, Si-O bonds and the hydrogen profile in the passivation layer, respectively. The result reveals that the single layer of AlOx provides good field effect with a large amount of negative Qf. Furthermore, SiOx capping on AlOx have more excellent chemical passivation because of amount of H saturate the dangling bonds on the silicon surface.

Simple method for significant improvement of minority-carrier lifetime of evaporated BaSi2 thin film by sputtered-AlOx passivation

A novel surface passivation of AlOx on BaSi2 thin films fabricated by vacuum evaporation for solar cell application has been developed. The minority-carrier lifetime of evaporated BaSi2 film is shorter than that of epitaxial film. This lifetime has been improved by forming AlOx passivation layer on the BaSi2 surface by RF sputtering of Al followed by oxidation in air. A drastic improvement of the lifetime upon the passivation of AlOx was observed up to 15μs with 3-nm of AlOx layer after rapid thermal annealing at 475°C for 15min. The dependence of lifetime on passivation layer thickness disappeared for thickness higher than 9nm, especially after annealing, showing the chemical passivation effect of AlOx. The result confirmed that AlOx is a promising passivation-layer for improving properties of BaSi2 film.

Hydrogen passivation of silicon/silicon oxide interface by atomic layer deposited hafnium oxide and impact of silicon oxide underlayer

HfO2 synthesized by atomic layer deposition (ALD) can be used as a passivation material for photodetectors. This paper shows a significant reduction of density of interface traps at the Si/SiO2 interface using ALD HfO2. This is explained by a chemical passivation effect due to presence of hydrogen from water used in the ALD process. Furthermore, ALD HfO2 layers appear negatively charged which generate an additional field effect passivation. The impact of the SiO2 underlayer is also discussed by comparing a chemical silicon oxide to a standard thermal silicon oxide. It is shown that chemical silicon oxide can act as a reservoir of hydrogen atoms which helps to reduce the density of defects close to the Si/SiO2 interface. This result demonstrates the importance of the surface preparation before the ALD of HfO2 in the passivation scheme. Finally, this work shows the correlation between negatively charged defects and Si–O–Hf bonds at the SiO2/HfO2 interface. A passivation stack composed of chemical oxide permits to reach both a low density of interface traps (∼1.0 × 1011 cm−2 eV−1) and a negative charge density (∼−1.0 × 1011 cm−2). This stack provides both chemical and field effect passivation of the silicon surface.

Optical and electrical properties of nanostructured implanted silicon n+-p junction passivated by atomic layer deposited Al2O3

This paper investigates the optical and electrical properties of nanostructured implanted silicon junctions passivated by Al2O3 layers. A two-step ion implantation method has been developed to fabricate the nanostructured n+-p junctions with theoretical support of two dimensional Monte Carlo simulations to predict and optimize the junction profile. Dense and uniform arrays of silicon nanopillars and nanocones were formed by combining nanosphere lithography and dry etching, exhibiting a low reflectance in a broad spectrum from 300 to 800nm. A conformal Al2O3 layer was deposited on the array by using thermal atomic layer deposition (ALD) to achieve chemical passivation effect. External quantum efficiency and power conversion efficiency of the junctions were measured versus nanostructuration and Al2O3 passivation. The results showed that significant enhancement of efficiency can be achieved on the passivated nanopillar-based junctions.

Impact of front-side point contact/passivation geometry on thin-film solar cell performance

In this work, we perform an extensive campaign of three-dimensional numerical simulations of CIGS solar cell structures to investigate the effect of a surface-passivated CIGS with point contacts openings on the cell performance parameters (Jsc, Voc, FF and η). Detailed analysis of the combination of passivation thickness, point contact size and pitch is performed under the hypothesis of highly defective CIGS front surface and ideal chemical passivation: efficiencies close to the case of ideal (i.e., defect-free) CdS/CIGS interface can be achieved by optimized nanometer-scale point contact arrays. To account for field-effect passivation due to positive residual charge density, Qf, within the passivation layer, we vary Qf in the range 1010–1013cm−2 under the two extreme scenarios of ideal or ineffective chemical passivation. Several examples of CIGS cells with different buffer layers (CdS, ZnO, ZnMgO, In2S3, Zn(O, S)) are also analyzed. We find that a positive Qf in the interval 1012– 5·1012cm−2 can help completely recover the ideal cell efficiency, irrespective of the chemical passivation effect and even in the presence of unfavorable conduction band alignment at the buffer/CIGS heterojunction. This may help devising solutions with buffer materials alternative to CdS, boosting the performance of otherwise surface-limited cells. The effect of grain boundary defect density and position with respect to point contacts is also addressed, with a grain dimension of 750nm.

Surface studies of high voltage lithium rich composition: Li1.2Mn0.525Ni0.175Co0.1O2

This article reports the evidence of surface film formation due to the oxidation of electrolyte upon high voltage cycling (4.9 V) of the lithium rich cathode, Li1.2Mn0.525Ni0.175Co0.1O2. We have studied the chemical composition of this surface film using electrochemical impedance, X-ray Photoelectron and micro-Raman spectroscopies and the results are compared against the pristine electrode. In order to distinguish the changes in the surface film composition induced by prolonged electrochemical cycling versus chemical passivation effect, we studied the surface composition of cathode powders aged with electrolytes at 60 °C. Our results show that after 150 cycles, the electrodes showed a rapid drop in capacity due to increase in the surface film resistance resulting in limited capacity utilization.

A Brillouin scattering study of the effect of chemical passivation on the elastic properties of porous silicon

Brillouin scattering has been performed to probe acoustic waves in porous silicon films that have been chemically modified with either 1-decene, decyl aldehyde, undecylenic acid, or ethyl undecylenate. The shift in the frequencies of acoustic modes in the passivated porous silicon samples, relative to those in freshly prepared porous silicon, is different for different chemical modifiers. The magnitude of the frequency shift is qualitatively correlated with the change, caused by the passivation, in the average densities and elastic constants of the samples.

Quality evaluation and improvement of iron-doped electromagnetic multycrystalline silicon wafers

The effect of iron doping in electromagnetic cast (EMC) Si wafers on minority carrier recombination lifetime has been extensively investigated by means of microwave detected photo-conductivity decay (μ-PCD) and surface photo-voltage (SPV) to discriminate impurities and defects for the lower crystal quality. Optical and thermal activations of doped iron are investigated to study the difference between the two techniques in obtaining iron concentration. Minority carrier lifetimes increase or decrease after activation due to the different optical injection levels of both the SPV and μ-PCD techniques. No noticeable effect of chemical passivation in obtained iron concentration is observed. Boron and phosphorus gettering and hydrogen passivation techniques are applied to improve minority carrier recombination lifetime. As a result, the crystal quality of the EMC Si wafers depends on defect centers rather than on iron impurities.

Epitaxial growth of ZnS on bare and arsenic-passivated vicinal Si(100) surfaces

We report a detailed study of molecular beam epitaxial growth of ZnS films on bare and arsenic-passivated vicinal Si(100) surfaces. This study elucidates the initiation of microtwinning and stacking-fault defects on double-stepped substrate surfaces. The study also sheds light on the function of arsenic passivation in reducing crystal defects in ZnS epitaxial layers. Three substrate surfaces, Si(100) 2×1, Si(100):As 2×1, and Si(100):As 1×2, were used for the ZnS epitaxial growth studies. Adsorption experiments were performed to demonstrate the chemical passivation effect of an arsenic overlayer. Reflection high-energy electron diffraction was used to study growth modes and the epitaxial relationship of the ZnS layers to the substrates. Transmission electron microscopy was used to study the crystal-defect structures. Secondary ion mass spectroscopy was used to determine the chemical profiles of the heteroepitaxial interfaces of ZnS layers grown on arsenic-passivated surfaces. One of the main results demonstrated by this work is that thin ZnS films can be grown epitaxially with much better crystal quality on As-passivated Si surfaces than on bare Si surfaces.