Showing papers on "Polysilicon depletion effect published in 2022"

A Polysilicon Learning Curve and the Material Requirements for Broad Electrification with Photovoltaics by 2050

Abstract: Herein, the current and future projected polysilicon demand for the photovoltaic (PV) industry toward broad electrification scenarios with 63.4 TW of PV installed by 2050 is studied. The current polysilicon demand by the PV industry in 2021 is equivalent to the consumption of 2.9–3.3 kt GW−1. Depending on the physical constraints determining the lower limit for future polysilicon consumption, the annual demand can be 6–7 Mt year−1 in 2050 under broad electrification, which requires 10–12 times more of the current production capacity. To achieve broad electrification by 2050, cumulative demand of 46–87 Mt is required. An electricity requirement for purification, ingot pulling, and wafering of ≈360–380 kWh kg−1 for silicon wafers and carbon intensity can lead to a cumulative amount of ≈16.4–58.8 Gt of CO2‐eq emissions by 2050. To reduce the environmental impact, efficiencies are increased, thinner wafers are used, kerf loss reduced, alternative purification methods with low emission intensities are explored, and opportunities for polysilicon production with decarbonized electricity are explored.

Comparing the Gettering Effect of Heavily Doped Polysilicon Films and Its Implications for Tunnel Oxide‐Passivated Contact Solar Cells

Abstract: In addition to excellent surface passivation and carrier selectivity, the structure based on the heavily doped polysilicon layer on an ultrathin silicon oxide interlayer also demonstrates strong impurity gettering effects. Herein, the gettering strength of a range of phosphorus‐ or boron‐doped polysilicon films from different fabrication techniques is assessed and compared. Iron, one of the most common metallic impurities in silicon, is used as a tracer impurity to quantify the gettering strength (segregation coefficient). A comparison of the experimental results to the literature, combined with measurements of the electrically active and inactive dopant concentrations, enables us to suggest the main gettering mechanisms in different polysilicon films. The differences in the segregation coefficients of the phosphorus‐doped polysilicon films for iron are within one order of magnitude, in spite of their different combinations of gettering mechanisms. On the other hand, boron‐doped polysilicon films show a large variation in their gettering effects, although the predominant gettering mechanisms are all attributed to electrically inactive boron, according to the current understanding of the gettering mechanisms from the literature. Finally, the impact of different polysilicon gettering effects on the efficiency of tunnel oxide‐passivated contact (TOPCon) cells is simulated and discussed.

Low doping in-situ strategy leading to polysilicon based TFTs exhibiting high stability under stress effects and enhanced electrical performances

Abstract: In the present work, we investigate the effect of low phosphorus doped polysilicon thin films. These later are deposited on glass substrates by low pressure chemical vapor Deposition (LPCVD) technique and are in situ doped with phosphine adjunction to silane. Doping levels are reported by the phosphine to silane ratio Γ varying from 0 (undoped layer) to heavily doped layer almost 1.2 × 10–3. Films are characterized by different techniques as Photothermal Deflection Spectroscopy (PDS), photoluminescence measurements and x-ray diffraction of polycrystalline layers. The last one reveals that doping concentration giving modification in crystallite size and presence of microstrain, so a clear reduction in the Eg value was observed for the slightest doped layer (Γ = 3.7 × 10–7) by comparaison with the undoped one ((Γ = 0). Results give evidence of an optimum doping level to obtain higher polysilicon films quality. Polysilicon film quality has been correlated to phosphorus doping levels. Thin film transistors (TFTs) are fabricated on glass substrate using a top gate four mask process at low temperature (<600 °C). Electrical characterizations highlight significant improvements in the TFTs performances using slightly doped film instead of undoped one as active layer. Based on Levinson’s model, density of states within the grain boundaries is also found to be the lowest. Stability under stress is enhanced too. For slightly doped films, electrical characterizations indicate that both threshold voltage Vth and density of states NT within the grain boundaries have their lowest values. Although, the field effect mobility μ records its highest values. Additionally, low doping levels enhances the TFT stability under stress. As a result, the in situ low doping strategy opens the way to manufacture polysilicon electronic devices exhibiting high electrical performances and a rather high stability under stress effects.

Mass production of crystalline silicon solar cells with polysilicon‐based passivating contacts: An industrial perspective

Abstract: Silicon solar cells that employ passivating contacts featuring a heavily doped polysilicon layer on a thin silicon oxide (TOPCon) have been demonstrated to facilitate remarkably high cell efficiencies, amongst the highest achieved to date using a single junction on a silicon substrate. Importantly, it has been shown that the polysilicon‐based passivating contacts have a high degree of compatibility with existing mass production processes and toolsets, making them an attractive choice for photovoltaic (PV) cell manufacturers to increase the efficiency of their products. With several large PV manufacturers recently announcing plans to push the TOPCon technology into mass production, we review the significant industrial research and development activities that have been undertaken to push the boundaries of the technology and optimise its integration into the existing mass production pipeline. From an industrial perspective, TOPCon fabrication methodology options as well as necessary technological advances in front‐side fabrication, cell metallisation and module integration are discussed. The TOPCon technology development is contextualised in terms of larger trends in PV manufacturing, and we look towards the direction of future industrial development.

Simplified EKV model parameter extraction in polysilicon MOSFETs

Abstract: We present an easy but effective method to extract the four parameters of the simplified Enz–Krummenacher–Vittoz (sEKV) MOSFET model. The procedure, which is based on direct lateral optimization, is tested using measurements from experimental polycrystalline silicon Thin Film Transistors (TFTs) of various channel lengths and widths. We demonstrate that this basic MOSFET model is able to reasonably describe the saturation transfer characteristics of these polysilicon TFTs. Furthermore, we evaluate the computational adeptness for extracting the four sEKV parameters of the lateral optimization fitting procedure as compared to the more traditional vertical optimization one.