Si Structures Research Articles

An artificial synapse based on La:BiFeO3 ferroelectric memristor for pain perceptual nociceptor emulation

Recently, memristors with brain-like synaptic behavior have attracted widespread attention, offering unprecedented opportunities for constructing future artificial intelligent bio-inspired electronic systems. Herein, we report a ferroelectric memristor with a Pd/La0.1Bi0.9FeO3(LBFO)/La0.67Sr0.33MnO3/SrTiO3/P+-Si structure, which exhibits the multilevel storage capacity of 12 resistive states, each with a retention time of 2 × 104 s and 200 ns ultra-fast pulse conductance modulation. Moreover, the synaptic properties are successfully mimicked, including paired-pulse facilitation, post-tetanic potentiation, and spike rate-dependent plasticity. In addition, pattern training with high tolerance to fault disturbance and variations is realized in the LBFO memristors array, endowing with highly accurate synaptic weights update capability. More importantly, the device can emulate essential characteristics of pain perception nociceptors with fast operating pulse and low threshold level, and a piezoresistive sensor is further introduced to integrate with LBFO memristor, realistically simulating the artificial pain perception function. Overall, the proposed device provides a promising avenue for the development of electronic skins, neurorobotics, and human–computer interaction technologies.

The effect of the addition of alumina on the viscosity, surface tension, and foaming efficiency of 2.5(CaO/SiO2)-xAl2O3-yFeO-MgO melts

Viscosity and surface tension strongly influence the efficiency of slag foam in metallurgical processes. An excellent foaming slag preserves heat and lowers the cost of smelting in an electric furnace. In this study, we investigated the viscosity, surface tension, and foaming efficiency of a 2.5CaO/SiO2-xAl2O3-yFeO-MgO slag. We also investigated the different valence oxygen ions by X-ray photoelectron spectroscopy (XPS). The results showed that with a gradual increase in the content of Al2O3, the viscosity initially increased and then decreased, and the changes in surface tension followed a similar pattern. The change in viscosity was caused by the increase in the degree of polymerization of the slag, which was determined by the competitive relationship between polymerization and the reduction in the stability of the overall network structure. Adding a small amount of Al2O3 to the slag slightly increased the number of Al–O–Al structures, whereas adding a large amount of the Al2O3 led to the formation of low-strength Al–O–Si structures, which reduced the stability of the network structure, thus reducing the viscosity. Because the surface tension is related to the concentration of non-bridging oxygens (NBOs), when the NBO content increased, the instability of the surface structure caused an increase in energy, thus increasing the surface tension. In addition, the CaO–SiO2–5MgO-xAl2O3-yFeO five-element oxide in this study had the lowest surface tension at the same NBO concentration, which positively contributed to slag foaming. Finally, When the Al2O3 content in the system increased from 5.1 to 15.7 wt%, the foaming efficiency increased from 24.2 to 69.2 (minute‧centimeters), an increase of 286%.

Understanding the changes in engineering behaviors and microstructure of FA-GBFS based geopolymer paste with addition of silica fume

Geopolymers are attracting attention as a new green cementitious material. However, the severe early drying shrinkage deformation of geopolymers limits the use of geopolymer materials in construction projects. Therefore, this study investigates the effect of silica fume (SF) on the drying shrinkage behavior of geopolymer composite. Fly ash (FA) and granulated blast furnace slag (GBFS) were activated by a combination of sodium hydroxide and water glass solutions to produce geopolymer paste. The modification mechanism of SF content on the drying shrinkage and mechanical properties of FA-GBFS geopolymer paste was studied, as well as the important effect of SF on the internal geopolymerization process of geopolymer composite. The results indicate that the SF changes the binding energy and relative content of Si–O-T (T: Si or Al) structure and tetrahedral coordinated Al–OH bond in FA-GBFS geopolymer composite, delaying the early geopolymerization and calcium silicate hydration reaction in the geopolymer. It diminishes the polymerization degree of gel structure in the geopolymer, which also lowers the early strength of the geopolymer paste. In addition, when the SF content reaches 20%, it not only improves the 28d compressive strength of FA-GBFS geopolymer, but also greatly reduces the relative content of harmful pores inside the geopolymer, which reduces the early drying shrinkage strain by about 50%.

The effect of the TiC-TiB2 nanoparticles on the microstructure and mechanical properties of Al-Mn-Si strips fabricated by twin-roll casting

In this work, Al-Mn-Si and TiC-TiB2/Al-Mn-Si strips were prepared by vertical-type twin-roll casting (TRC), and the effect of TiC-TiB2 nanoparticles (NPs) on the microstructure and mechanical properties of TRC Al-Mn-Si strips were studied. The TRC strips had the characteristics of coarse grains near the surface and fine grains in the center. The introduction of NPs resulted in the formation of uniform and fine grain structures due to the grain refinement effect of NPs. The refining effect on the surface grains was much greater than that on the central grains because the larger thermal undercooling of the melt at the surface led to the improvement of the nucleation efficiency of NPs. TiC-TiB2 particles could eliminate the central segregation of TRC Al-Mn-Si strips due to the control of solute diffusion by the uniform and fine grain structures, thereby reducing α-Al(Mn, Fe)Si formation in the central region. The mechanical properties of the TRC Al-Mn-Si strips were improved with the introduction of NPs. The yield strength at room temperature was increased from 79.0 MPa to 92.9 MPa, and the uniform elongation was increased from 7.2% to 10.1%, due to the fewer eutectic α-Al(Mn, Fe)Si, refined precipitates and grain structures caused by the addition of the TiC-TiB2 particles.

In Situ Evaluation of Cellular Spheroid Stiffness by Pinching Device Composed of Piezoactuator and Strain Gauge

Mechanical characterization of cells is important for understanding their behavior. This paper reports on an in situ evaluation of the stiffness of cellular spheroids using a pinching device. The pinching device is integrated with a bimorph piezoactuator and strain gauge. It can pinch an object by combining a piezo bimorph actuator and a thin Si structure and can detect the reaction force from an elastic object using a strain gauge integrated into the thin Si structure. The strain gauge can detect the bending deformation of the device and estimate the reaction force by considering actuation. This paper presents the design of the pinching device and experimental results when used for the in situ evaluation of the stiffness of cellular spheroids. © 2023 Institute of Electrical Engineers of Japan. Published by Wiley Periodicals LLC.

MXene-Based Memristor for Artificial Optoelectronic Neuron

With high efficiency and low energy consumption, bio-inspired artificial neuromorphic systems are regarded as the next generation of computing methods and have attracted tremendous attention in recent years. In bio-inspired artificial neuromorphic systems, multi-functional artificial neurons function as processing units to process complex information with high efficiency. However, the majority of reports on artificial neurons are based on electrical stimulation, whereas light-simulated neurons receive less attention. In this work, an artificial optoelectronic neural device based on an Ag/MXene/SiO2/Si structure is demonstrated. By introducing an oxidized MXene (O-MXene) layer, photoelectric integration can be realized on a single device. Compared to pure electrical stimulation, the synergistic effect of light and electrical stimulation can efficiently accelerate the firing behavior of neurons. In addition, we successfully designed and demonstrated a <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$64\times64$ </tex-math></inline-formula> sensing array based on optoelectronic neurons to recognize and sharpen the input signal trajectory. The proposed artificial optoelectronic neural device shows great potential for optoelectronic neuromorphic systems and is expected to promote the development of multifunctional, high-performance neuromorphic systems.

Effects of direct aging treatment on microstructure, mechanical properties and residual stress of selective laser melted AlSi10Mg alloy

• The as-fabricated microstructure benefits short-circuit diffusion of Si. • Direct aging treatment promotes unique precipitation behaviors. • Direct aging removes roughly 40% of the residual stress. • Mechanisms of residual stress removal are explored. • Over-aging treatment produces better mechanical properties. Direct aging treatment is an important post-processing procedure, yet little research has been done on how it balances the mechanical properties and the stress removal for selective laser melted (SLMed) AlSi10Mg alloys. Here, we proposed a typical direct aging treatment on SLMed AlSi10Mg alloys, and studied the effects on their microstructure, properties and residual stress evolution. The results indicate that the as-built microstructure is mainly composed of fine cellular α-Al and reticulated Si phases, and some pre-existing precipitates and dislocations are found in these cells. The direct aging treatment promotes the precipitation of the nano-scaled Si phase and preserves the network-like Si structure. Therefore, the strength of the peak-aged alloy increases while the ductility decreases. As the aging temperature increases from 160 to 200°C, aging hardening behavior was accelerated significantly. Aging at 160 °C for 4-9 h removes 32.0%-43.0% of the residual stress, which is attributed to the decomposition of the supersaturated α-Al matrix, the precipitation of the nano-Si phase and the exposure of low-angle grain boundaries (LAGBs). Considering the overal alloy performance obtained, over-aging at 160°C for 4 h is the optimized heat treatment regime. Under this condition, the yield strength (YS), ultimate tensile strength (UTS) and elongation (EL) of the alloy in the transverse and longitudinal direction are 309.5 MPa, 464.4 MPa and 8.3% and 286.4 MPa, 464.9 MPa and 5.1%, respectively.

Carbon-fibre-reinforced-PEEK and silicon doped amorphous carbon as a potential tribopair for implant application

ABSTRACT Studies pertaining to the evaluation of temperature rise in bio-tribopairs are scarce. The present work analyses the application of Si-doped amorphous carbon (Si:a-C) and carbon-fibre-reinforced-PEEK (CFRPEEK) as a potential metal-on-polymer acetabular articulation. The structure of the materials was studied using XRD and Raman spectroscopy and the mechanical behaviour of the Si:a-C film was evaluated using nanoindentation test and Rockwell-C indentation test. Si incorporation resulted in improved hardness and elastic modulus of a-C film along with appreciable H/E and H3/E2 attributes. The structure of Si:a-C film presented SiC phase with reduced sp2 clustering which results in lower graphitisation. CFRPEEK showcased crystalline structure with disorderness induced due to the introduction of carbon fibre. What is more, during lubricated sliding, the temperature rise in the sliding interface was obtained using thermocouple installed in the CFRPEEK counterbody near the sliding vicinity. The results showed low friction coefficient due to the formation of SiOx phase during sliding with low temperature rise having coefficient of 2.1. Si:a-C film underwent low fracture with patches of delamination and CFRPEEK suffered fibre pull-out and tearing. Further studies on the biological activities such as cell adhesion and bacterial adhesion can mainstream the application of these materials for implants.

Thermal annealing effects on the physical properties of GaAsBi/GaAs/GaAs:Si structure

GaAsBi is a new material called a highly mismatched alloy that has drawn attention regarding its special physical properties. The alloying of the GaAs matrix by Bi atom gives rise to a huge restructuring of the band structure. A rapid shrinkage in the bandgap energy and a splitting of the spin–orbit interaction band are noted. But the synthesis of this material requires unusual growth conditions in order to avoid the appearance of droplets on the surface and a native defects due to the non-stoichiometry. Consequently, an improvement of the physical properties is required to be used in device applications. In this perspective, we report an investigation of the effect of thermal annealing on the GaAsBi/GaAs/GaAs:Si structure. Photoreflectance, Spectroscopic ellipsometry are used to study the optical characteristics of this structure. High Resolution X-Ray Diffraction and Atomic Force Microscopy are employed as structural techniques for investigation.

X-Ray Diffraction of Ramp-Compressed Silicon to 390GPa.

Silicon (Si) exhibits a rich collection of phase transitions under ambient-temperature isothermal and shock compression. This report describes insitu diffraction measurements of ramp-compressed Si between 40 and 389GPa. Angle-dispersive x-ray scattering reveals that Si assumes an hexagonal close-packed (hcp) structure between 40 and 93GPa and, at higher pressure, a face-centered cubic structure that persists to at least 389GPa, the highest pressure for which the crystal structure of Si has been investigated. The range of hcp stability extends to higher pressures and temperatures than predicted by theory.

A 3D biomimetic optoelectronic scaffold repairs cranial defects.

Bone fractures and defects pose serious health-related issues on patients. For clinical therapeutics, synthetic scaffolds have been actively explored to promote critical-sized bone regeneration, and electrical stimulations are recognized as an effective auxiliary to facilitate the process. Here, we develop a three-dimensional (3D) biomimetic scaffold integrated with thin-film silicon (Si)-based microstructures. This Si-based hybrid scaffold not only provides a 3D hierarchical structure for guiding cell growth but also regulates cell behaviors via photo-induced electrical signals. Remotely controlled by infrared illumination, these Si structures electrically modulate membrane potentials and intracellular calcium dynamics of stem cells and potentiate cell proliferation and differentiation. In a rodent model, the Si-integrated scaffold demonstrates improved osteogenesis under optical stimulations. Such a wirelessly powered optoelectronic scaffold eliminates tethered electrical implants and fully degrades in a biological environment. The Si-based 3D scaffold combines topographical and optoelectronic stimuli for effective biological modulations, offering broad potential for biomedicine.

Preparation and evaluation of high-transparent scratch-resistant thin films on plasma treated polycarbonate substrate

New simple aqueous sol–gel procedure has been used for producing hard transparent organic–inorganic coatings on polycarbonate (PC). Sol-gel thins films were prepared by mixing Si and Al aqueous alkoxides and applied on the plasma treated PC. Tetraethyl orthosilicate (TEOS), 3-glycidoxypropyltrimethoxysilane (GPTMS) and aluminum tri sec-butoxide were used as main precursors. Before applying coatings PC were treated by Dielectric Barrier Discharge (DBD) system being conducted at atmosphere pressure. The effects of temperature, sols volume ratios and aging time on the coatings properties were scrutinized. Chemical, structural, morphological, optical and mechanical analyses of the samples were done by ATR-FTIR, EDS, XRD, FE-SEM, TEM, UV/vis spectroscopy, ellipsometry, pencil hardness and eraser scratch methods. TEM results showed well-dispersed nano-particles in the liquid sol. All of the films showed higher average transmittance (89 %) than the raw PC (86 %) that was stemmed from the lower refractive index (1.481) than raw PC (1.58). Films indicated good adhesion onto the plasma treated substrates (5B). The pencil hardness of the PC substrate (4B) improved to 3H (8 pencil grade increment) with just a single layer coating (775 nm thickness) due to the preparation of new hard structures of interlocked Si and Al atoms.

Evaluation of chemical structure and Si segregation of Al/Si(111)

Control of diffusion and segregation of Si atoms through a thin metal layer from a stacked Si structure is one of the effective techniques to grow two-dimensional (2D) or ultrathin Si crystals. We have studied the formation of the Al layer with a flat surface and high crystallinity on a wet-cleaned Si(111) wafer by thermal evaporation in order to use it as a growth template for ultrathin Si crystals. Then, the impacts of the annealing in N2 ambient on the surface flatness, the Al crystallinity, and the chemical bonding features for the Al/Si(111) structure were investigated. A formation of a sub-nanometer Si layer on the Al(111) surface using Si segregation with keeping surface flatness was demonstrated by the control of annealing temperature.

Improvement of metallurgical properties of A356 aluminium alloy by AlCrFeSrTiBSi master alloy

Abstract A new AlCrFeSrTiBSi master alloy was manufactured by in situ synthesis in Al melt, and compared with AlBSr master alloy. Microstructures of A356 alloy modified with AlCrFeSrTiBSi master alloy were investigated, and the structural details of the new cast A356 alloy were evaluated by X-ray diffraction (XRD), optical microscopy (OM), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), microhardness and differential thermal analysis (DTA). AlBSr master alloy typically formed α-Al and granular SrB6 phases in A356, and the samples inoculated with AlCrFeSrTiBSi master alloy consisted of additionally AlCrFeSi phase with irregular blocks. The addition of 0.1 wt%AlCrFeSrTiBSi alloy to the A356 alloy significantly refined and modified the grain structure together. The structure of eutectic Si converted from acicular form to fibrous. The size of α-Al dendrites declined from ∼1000 μm to ∼100 μm. The strength values of the A356 alloy were developed by ∼70% with the addition of 0.1 wt%AlCrFeSrTiBSi master alloy.

Homogeneous nucleation of crystalline methane hydrate in molecular dynamics transition paths sampled under realistic conditions.

Methane hydrates are important from a scientific and industrial perspective, and form by nucleation and growth from a supersaturated aqueous solution of methane. Molecular simulation is able to shed light on the process of homogeneous nucleation of hydrates, using straightforward molecular dynamics or rare event enhanced sampling techniques with atomistic and coarse grained force fields. In our previous work [Arjun, T. A. Berendsen, and P. G. Bolhuis, Proc. Natl. Acad. Sci. U. S. A. 116, 19305 (2019)], we performed transition path sampling (TPS) simulations using all atom force fields under moderate driving forces at high pressure, which enabled unbiased atomistic insight into the formation of methane hydrates. The supersaturation in these simulations was influenced by the Laplace pressure induced by the spherical gas reservoir. Here, we investigate the effect of removing this influence. Focusing on the supercooled, supersaturated regime to keep the system size tractable, our TPS simulations indicate that nuclei form amorphous structures below roughly 260K and crystalline sI structures above 260K. For these temperatures, the average transition path lengths are significantly longer than in our previous study, pushing the boundaries of what can be achieved with TPS. The temperature to observe a critical nucleus of certain size was roughly 20K lower compared to a spherical reservoir due to the lower concentration of methane in the solution, yielding a reduced driving force. We analyze the TPS results using a model based on classical nucleation theory. The corresponding free energy barriers are estimated and found to be consistent with previous predictions, thus adding to the overall picture of the hydrate formation process.

Second harmonic generation and simplified bond hyperpolarizability model analyses on the intermixing of Si/SiGe stacked multilayers for gate-all-around structure

Si/SiGe stacked multilayers are key elements in fabrication of gate-all-around (GAA) structures and improvement of electrical properties, with the evolution of the Si/SiGe interfaces playing a crucial role. In this work, a model is developed based on the simplified bond hyperpolarizability model (SBHM) to analysis the anisotropic reflective second harmonic generation (Ani-RSHG) on a three-period stacked Si/Si1−x Ge x multilayer, which builds on Si(100) diamond structures. The C 4v symmetry of the Si(100) structure enables the second harmonic generation (SHG) contribution from the bonds to be simplified and the effective hyperpolarizabilities of the interfacial and bulk sources to be obtained. The effective interface dipolar and bulk quadrupolar SHG hyperpolarizabilities in the Si1−x Ge x sample with various Ge concentration profiles are modeled by interpreting the concentration of a component element as the probability of the element occupying an atomic site. On the basis of the developed model, the Ani-RSHG spectra of the as-grown samples with various Ge ratios for each layer and the samples annealed at 850 °C and 950 °C are analyzed to inspect the change in Ge distribution and its gradient in depth. The ani-RSHG analysis on as-grown samples showed difference in Ge distribution in samples with the multi Si/SiGe structure, which is not well observed in synchrotron x-ray diffraction (XRD) spectra. For the annealed samples, the response to changes in Ge concentration and its gradient in depth reveal the Si/Si1−x Ge x interface intermixing. Results of high-angle annular dark-field scanning transmission electron microscopy and energy dispersive x-ray spectroscopy agree well with the Ani-RSHG with SBHM findings. Compared with the Raman and synchrotron XRD spectra, the Ani-RSHG with SBHM simulation result demonstrates much better response to changes in compositions of the Si/Si1−x Ge x stacked multilayered structures, verifying the potential for characterizing the concentration distribution in stacked multilayered thin films for GAA structures.

Optical study on mesa structures with adjustable absorption based on Mn1.56Co0.96Ni0.48O4 thin films

In order to improve the infrared detection performance, mesa structures of Mn1.56Co0.96Ni0.48O4/Aluminum/Silicon dioxide/Silicon (MCN/Al/SiO2/Si) were prepared by chemical solution deposition method. Raman spectroscopy results indicate that increasing the thickness causes a change in the Mn3+–O band stretching vibration and the Mn4+–O band bending vibration. Spectroscopic elllipsometry was used to obtain the dielectric function of the films by fitting the experiment data using the classical middle-infrared dispersion formula. The evaluated real part of the dielectric constants ε1 and refractive index n decreased as the wavelength increase, the imaginary part ε2 and extinction coefficient k monotonically increased as the wavelength increase in the entire measuring range of 2–10 μm. The calculated absorption spectra of the MCN/Al/SiO2/Si structure showed that the absorption peak position could be adjusted by varying the thickness of the MCN films. Our results are important in the design and application of MCN film infrared detectors.

Lead-Free Piezoelectric Ceramic Micro-Pressure Thick Films

In this study, non-stoichiometry lead-free piezoelectric ceramic Li0.058(K0.48Na0.535)0.966(Nb0.9Ta0.1)O3 (LKNNT) thick films were deposited on Pt/Ti/Si substrates using spin-coating method technology to form a LKNNT/Pt/Ti/Si structure of the micro-pressure thick films. Additionally, the influence on the crystalline properties, surface microstructure images, and mechanical properties, and the piezoelectric properties of the non-stoichiometry lead-free piezoelectric ceramic Li0.058(K0.48Na0.535)0.966(Nb0.9Ta0.1)O3 (LKNNT) thick films were observed, analyzed, and calculated using X-ray diffraction (XRD), field-emission scanning electron microscopy (FE-SEM), focused ion beam (FIB) microscopy, nano-indention technology, and other instruments. This study was divided into two parts: The first part was the investigation into the fabrication parameters and properties of the bottom layer (Pt) and buffer layer (Ti). The Pt/Ti/Si structures were achieved by the DC sputtering method, and then the rapid thermal annealing (RTA) post-treatment process was used to re-arrange the grains and reduce defects in the lead-free Li0.058(K0.48Na0.535)0.966(Nb0.9Ta0.1)O3 (LKNNT) thick films. In the second part, lead-free Li0.058(K0.48Na0.535)0.966(Nb0.9Ta0.1)O3 (LKNNT) powder was prepared by the solid-state reaction method, and then acetic acid (C2H4O2) solvent was added to form a slurry for spin-coating technology processing. The fabrication parameters, thick film micro-structure, crystalline properties, nano-indention technology, and the piezoelectric coefficient characteristics of the developed lead-free Li0.058(K0.48Na0.535)0.966(Nb0.9Ta0.1)O3 (LKNNT)/Pt/Ti/Si structure of the micro-pressure thick film devices a were investigated. According to the experimental results, the optimal fabrication processing parameters of the lead-free Li0.058(K0.48Na0.535)0.966(Nb0.9Ta0.1)O3 (LKNNT) were an RTA temperature of 500 °C, a Ti buffer-layer thickness of 273.9 nm, a Pt bottom electrode-layer thickness of 376.6 nm, a theoretical density of LKNNT of 4.789 g/cm3, a lattice constant of 3.968 × 10−8 cm, and a d33 value of 150 pm/V. Finally, regarding the mechanical properties of the micro-pressure devices for when a microforce of 3 mN was applied, the thick film revealed a hardness of 60 MPa, a Young’s modulus of 13 GPa, and an elasticity interval of 1.25 μm, which are suitable for future applications of micro-pressure devices.

Diverse Reactions of o-Carborane-Fused Silylenes with C≡E (E = C, P) Triple Bonds.

The reactivities of o-carborane-fused silylenes toward molecules with C≡E (E = C, P) bonds are reported. The reactions of bis(silylene) [(LSi:)C]2B10H10 (1a, L = PhC(NtBu)2) with arylalkynes afforded bis(silylium) carborane adducts 2 and 3, showing a Si(μ-C2)Si structure with an open-cage nido-carborane backbone. In contrast, the reaction of 1a with a phosphaalkyne AdC≡P (Ad = 1-adamantyl) smoothly furnished compound 4, comprising fused CPSi rings with a C=Si double bond and Si-Si single bond, and the related formation mechanism was investigated by DFT calculations. Furthermore, when monosilylene [(LSi:)C]CHB10H10 (1b) was employed to react with AdC≡P, compound 5 was isolated. The structure of 5 features a 1,2,3-triphosphetene core. All products were characterized by NMR spectroscopy and/or X-ray crystallography.

Simulation of CdS/p-Si/p+-Si and ZnO/CdS/p-Si/p+-Si heterojunction solar cells

In this study, the antireflection effect of CdS and ZnO/CdS layers was investigated via computing and solar cell I-V graphs and efficiency of the solar cell is simulated using the SCAPS. The lowest average reflectance value for single layer CdS was calculated as 13.43 %, for ZnO/CdS double layer 9.46 %. The efficiency values of CdS/p-Si/p+-Si and ZnO/CdS/p-Si/p+-Si heterojunction solar cells were calculated by changing the CdS and ZnO thicknesses from 40 nm to 80 nm. The highest efficiency value for the CdS/p-Si/p+-Si structure was calculated as 20.30 %. The efficiency value for the ZnO/CdS/p-Si/p+-Si heterojunction solar cell was increased to 21.82 % with the effect of the ZnO layer.