Showing papers on "Polycrystalline silicon published in 2023"

MEMS Reliability: On-Chip Testing for the Characterization of the Out-of-Plane Polysilicon Strength

Abstract: Polycrystalline silicon is a brittle material, and its strength results are stochastically linked to microscale (or even nanoscale) defects, possibly dependent on the grain size and morphology. In this paper, we focus on the out-of-plane tensile strength of columnar polysilicon. The investigation has been carried out through a combination of a newly proposed setup for on-chip testing and finite element analyses to properly interpret the collected data. The experiments have aimed to provide a static loading to a stopper, exploiting electrostatic actuation to move a massive shuttle against it, up to failure. The failure mechanism observed in the tested devices has been captured by the numerical simulations. The data have been then interpreted by the Weibull theory for three different stopper sizes, leading to an estimation of the reference out-of-plane strength of polysilicon on the order of 2.8–3.0 GPa, in line with other results available in the literature.

Effect of Molybdenum Disulphide Thin Films on Enhancing the Performance of Polycrystalline Silicon Solar Cells

Abstract: This research work focuses on augmenting the power conversion efficiency of the polycrystalline silicon solar cell with the aid of antireflection coating (ARC) of synthesized molybdenum disulphide (MoS2). The sol-gel technique and electrospraying method were preferred for synthesizing and depositing MoS2 as transparent thin films on the surface of the solar cells. The optical, electrical, structural, and thermal properties of the coated solar cells were analyzed for understanding the influence of the MoS2 coating. Five different samples (A-II, A-III, A-IV, A-V, and A-VI) were coated with varying coating time. Among them, 120 min coated sample experienced a maximum power conversion efficiency (PCE) of 17.96% and 18.82% under direct sunlight and neodymium light with resistivity as low as 2.79 × 10 − 3 Ω − cm . The investigation of optical properties of the coated solar cells revealed a maximum transmittance of 93.6% and minimum reflectance of 6.3%, achieved for A-IV sample in the visible UV spectrum. Sample A-IV showed prominent results in the temperature analysis with temperatures as low as 38.9°C in uncontrolled and 43.2°C in controlled source environments. The results from various analyses proved that MoS2 was an appropriate material for an antireflection coating to enhance the performance of polycrystalline solar cell.

Editorial: Passivating contact solar cells

Abstract: In the last decade, significant attention has been given to the concept of passivating contact solar cells. Such cells are characterised by very low contact recombination and low contact resistance, a combination that is challenging to achieve with conventional diffused silicon layers. These cells demonstrate a very high open-circuit voltage and therefore higher efficiency. Passivating contacts can be classified into three main technologies according to the material used for the chargecarrier selection: (i) doped amorphous silicon; (ii) doped polycrystalline silicon; and (iii) metal compounds and organic materials. Due to the impressive progress of passivating contacts and the wide variety of technologies and approaches, Progress in Photovoltaic decided to dedicate an entire issue to reviewing the status of this concept. The issue starts with a review of the three main technologies of passivating contacts, summarising their current efficiencies and discussing their distinctive features, advantages, and limitations. While doped amorphous silicon has been used for the manufacturing of industrial heterojunction solar cells for decades, polycrystalline silicon-based solar cells have only recently entered mass production. Interestingly, this technology was introduced to bipolar transistors as early as the 1970s and adapted into silicon solar cells in the 1980s. However, because some aspects other than the contacts limited the obtainable solar cell efficiencies, this technology was not actively investigated until 2013. Nevertheless, since then, a substantial amount of research has been done by several research institutes and companies, enhancing the performance of polycrystalline silicon-based solar cells to efficiencies above 26%. More importantly, significant effort has been made to commercialise this technology with significant progress already reported by several photovoltaic companies. As doped polycrystalline silicon seems to be the most mature passivating contact technology, we review the status of the three leading approaches: The POLO of ISFH, the TOPCon of Fraunhofer ISE, and the monoPoly of SERIS. With several large manufacturers announcing their plans to transfer polycrystalline siliconbased technology into mass production, we also review the activities that have been taken to push the boundaries of this technology and enabled its integration into existing production lines. Manufacturing options, as well as necessary technological advances in cell metallisation and module integration, are discussed from the industrial perspective. We then review the progress of passivating contact technologies that employ metal compounds as the carrier-selective layer. The interest in this technology has recently increased with a few promising families of materials having demonstrated excellent results, specifically alkali/alkaline-earth metal compounds and transition-metal oxides. The number of successful demonstrations of selective-contact materials within these families is increasing fast, with the best solar cell efficiencies now exceeding 23%. The challenges of this technology to be considered for industrial adoption are then discussed, together with its prospects in the context of silicon photovoltaics. In a separate paper, we provide a detailed techno-economic analysis of the use of atomic layer deposited transition-metal oxides for the fabrication of silicon solar cells. The special issue concludes with a paper discussing the challenges and opportunities in the metallisation of industrial perovskite/silicon tandem solar cells. We want to thank all the authors for their great contributions. It was a pleasure to work with such a talented and diverse group of researchers.

Performance Analysis of Monocrystalline and Polycrystalline Solar Photovoltaic for Solar Water Pump (SWP) System in Indonesia

Abstract: Solar Water Pumps (SWP) systems have been widely developed, especially in remote rural areas that cannot be reached by the electricity network of the State Electricity Company. The most common obstacle is that water supply through the SWP system is still relatively expensive, especially if solar panels are combined with the use of batteries. This study aims to assess the performance of the water pumping system supplied by monocrystalline and polycrystalline solar panels without using batteries. The method used in this research is the observation method by first designing and installing the SWP system using monocrystalline and polycrystalline solar panels. The results showed that in the use of monocrystalline and polycrystalline solar panels in the SWP system, the average efficiency of the solar panels was 6.87% and 6.73%, the average pump efficiency 33.85% and 32.34%, and the global efficiency 2.30%, and 2.17%.

Массивы квазиодномерных нанокристаллов GaAs, выращенные на окисленной поверхности гетероструктуры Si/GaAs(001): влияние толщины эпитаксиального слоя Si на строение массива

Abstract: Structures with arrays of planar and tilted quasi-one-dimensional GaAs nanocrystals have been grown on GaAs(001) substrates. An epitaxial silicon layer oxidized in air was used as a passivation coating. The amount of silicon deposited varied from structure to structure and was equivalent to 1, 2, 4, and 6 atomic layers. It has been found that in the case of a passivation layer based on silicon with a thickness of 1 atomic layer, an array of planar nanocrystals is formed, and in other cases, inclined quasi-one-dimensional nanocrystals. Nanocrystals are surrounded by crystallites, the shape, size, orientation, and distribution density of which change with the amount of silicon. The lowest density of crystallites was achieved with a silicon layer 6 atomic layers thick.

Comparison of Efficiencies Using Thermal Characteristics of Different PV Materials Using ANSYS

Abstract: A photovoltaic cell converts the light energy coming from the sun into electrical energy using semiconductor materials through the photovoltaic effect. In the near future, fossil fuels are going to be exhausted, which indicates that we have to go with alternative energy. Solar energy is currently the most efficient, environmentally friendly, and renewable energy source on the planet. The major problem with solar panels is their conversion efficiency, which is severely affected by temperature. Nowadays, there are mainly four types of solar panels, namely thin film, amorphous silicon, monocrystalline silicon, and polycrystalline silicon, used to manufacture solar panels. The main aim of this paper is to give a comparison of the efficiencies of different photo voltaic cell materials based on their thermal profiles obtained from transient analysis. It focuses on the simulation of solar cells using the ANSYS software simulation tool and analysing thermal characteristics to find the efficiency.

Crystallization of Hydrogenated Amorphous Silicon Thin Films Using Combined Continuous Wave Laser and Thermal Annealing

Abstract: Abstract Hydrogenated amorphous silicon (a-Si:H) films were deposited using the plasma-enhanced chemical vapor deposition (PECVD) process on Corning glass substrates. An aluminum overcoat was deposited on the films. The specimens were irradiated with a continuous wave Ar + laser beam of varying power density and duration. The samples were then annealed at 250 o C for 15 minutes to convert the amorphous silicon into polysilicon film. The grain size of the polycrystalline silicon films varies by varying the laser power density and the exposure time. The polysilicon grains acquired diameters ranging from 0.4 to 1.25 µm when the laser power density was set between 74.7 W/cm 2 and 94.3 W/cm 2 . The grains with a size ranging between 1 and 2.5 µm showed plate-like and dendritic-like configurations when laser power densities changed between 31.4 and 74.7 W/cm 2 . The XRD analysis revealed polycrystalline silicon with expected relative strengths.

Size effects in the elastic properties of polycrystalline silicon

Abstract: Polycrystalline silicon has a wide range of applications in the semiconductor industry. Instead of components whose dimensions are of the same order of magnitude in all three spatial directions, thin slices are primarily used there. Deviating mechanical properties have been noticed among such thin configurations. In this work, we systematically investigate the size-dependent effective elastic properties of polycrystalline silicon. This is realized by gradually reducing the thickness of such components, starting from a structure usually referred to as representative volume element. Based on the framework of continuum mechanics, we specify unit cell problems for aggregates whose microstructures are build artificially based on first-order properties through tessellations. The effective responses of virtual material tests are determined by the aid of the finite element method. Based on a larger number of computational simulations with different but equivalent microstructures, the effective elastic properties of silicon polycrystals are evaluated statistically. The findings are examined with regard to geometrically-induced symmetries by several methods. For the unconstrained configurations examined here, results show an increase in the scattering of the results where the average stiffness decreases with decreasing structural thickness. These outcomes are also compared to analytical estimates for silicon bulk configurations. This comparison indicates that the average stiffness varies in between a reasonable mean and the isotropic first-order lower bound of the silicon bulk. Compared to experimental findings, admissible bounds of the stiffnesses are clearly outlined.

Efficiency Improvement of Industrial Silicon Solar Cells by the POCl3 Diffusion Process

Abstract: To improve the efficiency of polycrystalline silicon solar cells, process optimization is a key technology in the photovoltaic industry. Despite the efficiency of this technique to be reproducible, economic, and simple, it presents a major inconvenience to have a heavily doped region near the surface which induces a high minority carrier recombination. To limit this effect, an optimization of diffused phosphorous profiles is required. A “low-high-low” temperature step of the POCl3 diffusion process was developed to improve the efficiency of industrial-type polycrystalline silicon solar cells. The low surface concentration of phosphorus doping of 4.54 × 1020 atoms/cm3 and junction depth of 0.31 μm at a dopant concentration of N = 1017 atoms/cm3 were obtained. The open-circuit voltage and fill factor of solar cells increased up to 1 mV and 0.30%, compared with the online low-temperature diffusion process, respectively. The efficiency of solar cells and the power of PV cells were increased by 0.1% and 1 W, respectively. This POCl3 diffusion process effectively improved the overall efficiency of industrial-type polycrystalline silicon solar cells in this solar field.

Thermal conductivity of doped polysilicon layers

Abstract: Polycrystalline silicon is common in microdevices for which thermal design is important. This study measures the lateral thermal conductivity of a boron-doped polysilicon layer at temperatures ranging from 20 to 320 K. The polysilicon layer is 1 µm thick with a doping concentration of l×lO¹⁹ cm^-3, and the measurements are performed using electrical-resistance thermometry in a suspended membrane structure. The room temperature thermal conductivity of the doped polysilicon layer is 45.3 W/m K, which is nearly an order of magnitude lower than that for a single-crystal silicon layer with the same dopant concentration. Phonon transport modeling and AFM grain size measurements suggest that annealing in this sample strongly reduces the importance of grain-boundary scattering.

Ferroelectric Tunnel Thin-Film Transistor for Synaptic Applications

Abstract: A ferroelectric tunnel thin-film transistor (FeT-TFT) with polycrystalline-silicon (poly-Si) channel and ferroelectric HfZrOx gate dielectric is demonstrated with analog memory characteristics for the application of synaptic devices. The FeT-TFT exhibits a much lower conduction current of ~0.032 times in transfer characteristics and maximum conductance (Gd) of ~0.14 to 0.2 times in potentiation and depression operation than the FeTFT due to FeT-TFT’s carrier transport mechanism: interband tunneling. This work employed pulse widths of 75, 150, and 300 ns to modulate Gd, and it was found that using a pulse width of 75 ns could achieve low asymmetry ~1 and high Gd ratio ~20.63 under consideration of operation speed. When the pulse time is increased, the potentiation and depression voltages can be significantly decreased to maintain the low asymmetry, but the Gd ratio is also reduced. In addition, the endurance characteristic of poly-Si FeT-TFT is found to be strongly related to the degradation effect of subthreshold swing due to the dynamic stress effect in the endurance measurement. This result reveals that the reliability of ferroelectric devices is not only owing to the degradation of the remanent polarization.

Characterization of tunnel oxide passivated contact fabricated by sputtering and ion implantation technique

Abstract: Tunnel oxide passivated contact (TOPCon) structures using highly doped n-type polycrystalline silicon were fabricated using facing target sputtering and ion implantation techniques for a SiH4-free fabrication process of high-efficiency silicon solar cells. We investigated the structural and electrical properties of the highly doped n-type poly-Si layers to optimize the ion implantation process. We also investigated the surface passivation quality of our TOPCon structure. An effective carrier lifetime of 2.01 ms and an implied open circuit voltage of 704 mV were obtained for our sample annealed at 950 °C. The sample also exhibits a low contact resistance of 3.22 × 10−3 Ω cm−2. Our results open the way for SiH4-free fabrication of silicon solar cells with a TOPCon structure.

Abnormal Degradation Behaviors Under Negative Bias Stress in Flexible p-Channel Low-Temperature Polycrystalline Silicon Thin-Film Transistors After Laser Lift-Off Process

Abstract: This work investigates the abnormal phenomena that are observed in electrical characteristics under negative bias stress (NBS) in flexible p-channel low-temperature polycrystalline silicon thin-film transistors (p-channel LTPS TFTs) after TFTs being lifted off from a rigid substrate. During the lift-off process, mechanical strain accumulates in the buffer layer due to the unilateral force, thus resulting in the generation of defects in the buffer layer. Therefore, abnormal degradation behaviors in electrical characteristics of the lifted-off TFTs were observed during negative gate bias stress. A study on physical mechanisms is introduced to describe such abnormal phenomena, and it is confirmed that defects are produced in the buffer layer when the LTPS TFTs are lifted off. In addition, different device dimensions were discussed to support our proposed model. The findings in this work are supported by the discussion of electrical characteristics, trap state extraction, and COMSOL simulation.

Design and comparative analysis of grid-connected BIPV system with monocrystalline silicon and polycrystalline silicon in Kandahar climate

Abstract: Building integrated photovoltaic (BIPV) system is a new and modern technique for solar energy production in Kandahar. Due to its location, Kandahar has abundant sources of solar energy. People use both monocrystalline and polycrystalline silicon solar PV modules for the grid-connected solar PV system, and they don’t know that which technology performs better for BIPV system. This paper analysis the parameters, described by IEC61724 “Photovoltaic System Performance Monitoring Guidelines for Measurement, Data Exchange and Analysis” to evaluate which technology shows better performance for the BIPV system. The monocrystalline silicon BIPV system has a 3.1% higher array yield than the polycrystalline silicon BIPV system. The final yield is 0.2% somewhat higher for monocrystalline silicon than polycrystalline silicon. Monocrystalline silicon has 0.2% and 4.5% greater yearly yield factor and capacity factors than polycrystalline silicon respectively. Monocrystalline silicon shows 0.3% better performance than polycrystalline silicon. With 1.7% reduction and 0.4% addition in collection losses and useful energy produced respectively, monocrystalline silicon solar PV system shows good performance than polycrystalline silicon solar PV system. But system losses are the same for both technologies. The monocrystalline silicon BIPV system injects 0.2% more energy to the grid than the polycrystalline silicon BIPV system.

Effects of Polycrystalline Silicon Plug Defect on DRAM Characteristics

Abstract: This study first demonstrates the effect of polycrystalline silicon plug defects, including voids and seams in dynamic random access memory (DRAM) storage node contact (SNC), on product characteristics. The defect portion of SNC has increased continually due to a reduction in the contact area, an increase in the doping concentration, and low-pressure chemical vapor deposition (LPCVD) process limitations. We validate the effect through defect removal experiments. Numerous methods, such as the cyclic deposition/etch/deposition process of silicon, ion implantation, and laser annealing, are used. The experiments are successful without any side effects using a high-density laser annealing process. The contact resistance of the sample-removed polysilicon defect decreases by 59% and the cell drain current increases by 6%. In addition, the overlap capacitance of the drain node and cell gate edge (Cov) variations by the SNC dopant diffusion forming the source and drain junction of the cell transistor is improved by 6%. Finally, we conduct the row precharge delay from the last data-in (tRDL) time delay reliability test using mass production test technology and it was confirmed that the contact area standard that satisfies the product quality target is improved by 10%. We propose a new direction for polycrystalline silicon SNC development for a sub-20-nm DRAM device based on this experiment.

Crystalline silicon solar cells with thin poly-SiO x carrier-selective passivating contacts for perovskite/c-Si tandem applications

Abstract: Single junction crystalline silicon (c-Si) solar cells are reaching their practical efficiency limit while perovskite/c-Si tandem solar cells have achieved efficiencies above the theoretical limit of single junction c-Si solar cells. Next to low-thermal budget silicon heterojunction architecture, high-thermal budget carrier-selective passivating contacts (CSPCs) based on polycrystalline-SiO (poly-SiO ) also constitute a promising architecture for high efficiency perovskite/c-Si tandem solar cells. In this work, we present the development of c-Si bottom cells based on high-temperature poly-SiO CSPCs and demonstrate novel high-efficiency four-terminal (4T) and two-terminal (2T) perovskite/c-Si tandem solar cells. First, we tuned the ultra-thin, thermally grown SiO . Then we optimized the passivation properties of p-type and n-type doped poly-SiO CSPCs. Here, we have optimized the p-type doped poly-SiO CSPC on textured interfaces via a two-step annealing process. Finally, we integrated such bottom solar cells in both 4T and 2T tandems, achieving 28.1% and 23.2% conversion efficiency, respectively.

Technology of Secondary Cast Polycrystalline Silicon and Its Application in the Production of Solar Cells

Abstract: The technology of smelting one of the well-known modifications of multisilicon, namely, secondary cast polycrystalline silicon, is described, and options for its application for the production of a solar cell and the manufacture of heavily doped silicon substrates are described. The proposed multisilicon seems to be intentionally subjected to overdoping, which must be carried out by one or a group of impurities to the solubility limit and at the same time use a charge from a mixture of technical silicon of the highest grades. It is emphasized that the film growth as the base region of solar cells should be carried out under conditions of guaranteed suppression of autodoping by known methods. The requirements for the use of reverse technologies in the operations of obtaining raw Si during the buildup of the film base of solar cells are stated. The importance of using advanced techniques to control the process of the gas phase epitaxy of mathematical regression models has been studied.

Thickness-dependent carrier transport of PdSe2 films grown by plasma-assisted metal selenization

Abstract: Atomically thin narrow-bandgap layered PdSe2 has attracted much attention due to its rich and unique electrical properties. For silicon-compatible device integration, direct wafer-scale preparation of high-quality PdSe2 thin film on a silicon substrate is highly desired. Here, we present the low-temperature synthesis of large-area polycrystalline PdSe2 films grown on SiO2/Si substrates by plasma-assisted metal selenization and investigate their charge carrier transport behaviors. Raman analysis, depth-dependent x-ray photoelectron spectroscopy, and cross-sectional transmission electron microscopy were used to reveal the selenization process. The results indicate a structural evolution from initial Pd to intermediate PdSe2–x phase and eventually to PdSe2. The field-effect transistors fabricated from these ultrathin PdSe2 films exhibit strong thickness-dependent transport behaviors. For thinner films (4.5 nm), a record high on/off ratio of 104 was obtained. While for thick ones (11 nm), the maximum hole mobility is about 0.93 cm2 V−1 S−1, which is the record high value ever reported for polycrystalline films. These findings suggest that our low-temperature-metal-selenized PdSe2 films have high quality and show great potential for applications in electrical devices.