Ly Mai - Academia.edu (original) (raw)
Papers by Ly Mai
Custom-glazed terracotta tiles Application: Rain screen facade Properties of material: The terrac... more Custom-glazed terracotta tiles Application: Rain screen facade Properties of material: The terracotta material provides a ventilated and pressure-equalized enclosure that helps keep the building dry to reduce maintenance while also saving energy.
The use of Laser Doping technology to form a selective emitter on solar cells has proven to be si... more The use of Laser Doping technology to form a selective emitter on solar cells has proven to be simple, cost effective, and suitable for commercial production. Efficiencies in excess of 18% have consistently been demonstrated on industrial grade p-type CZ wafers. One of the most important aspects of the laser doping technology is to provide localised heavily doped regions without subjecting the entire wafer to high temperature processing. This feature facilitates its suitability for fabricating multicrystalline solar cells. Multicrystalline wafer material often degrades at high processing temperature. Nevertheless, there are still several challenges in adapting the laser doping concept to multicrystalline wafers, particularly due to the presence of grain boundaries. The front anti-reflection coating must not only allow the hydrogenation effect to take place in passivating the bulk material but also protect the wafers against laser induced defects and be sufficiently dense to act as a plating mask. In this work, double stack layers of silicon oxy-nitride and silicon nitride (SiNx) are used as anti-reflection coating for the front surface. The passivation effects of these stacked layers, along with its ability to withstand laser induced defects will be discussed in this paper. Reflection properties of the silicon oxy-nitride single layer and the silicon oxy-nitride/silicon nitride double stack layers antireflection coatings are examined.
In this paper, we report on the effect of different annealing processes on rear side AlOx/SiNx st... more In this paper, we report on the effect of different annealing processes on rear side AlOx/SiNx stack passivation and the effect of AlOx thickness on implied open circuit voltage (iVoc) loss during laser doping using the AlOx layer and an additionally applied boron spin-on-dopant layer as a dopant source. Thin layers of AlOx capped by SiNx show improved iVoc after thermal annealing with slightly higher values observed after a 700oC peak temperature firing process than a conventional 400oC anneal. For thicker layers, blistering is observed after the firing process resulting in substantially lower iVoc than wafers annealed at 400oC. The improved passivation provided by thinner layers annealed at 400 oC is attributed to more effective hydrogen diffusion into the bulk of the wafers. When laser doping through the AlOx layers, thick AlOx layers result in lower voltage loss; however, the iVoc value degrade upon subsequent annealing. On the other hand, thin AlOx layers show a substantial improvement upon the same annealing process.
IEEE Journal of Photovoltaics, 2021
The integration of nanotextured black silicon (B-Si) into solar cells is often complicated by its... more The integration of nanotextured black silicon (B-Si) into solar cells is often complicated by its enhanced phosphorus doping effect, which is typically attributed to increased surface area. In this article, we show that B-Si's surface-to-volume ratio, or specific surface area (SSA), which is directly related to surface reactivity, is a better indicator of reduced sheet resistance. We investigate six B-Si conditions with varying dimensions based on two morphology types prepared using metal-catalyzed chemical etching and reactive-ion etching. We demonstrate that for a POCl 3 diffusion, B-Si sheet resistance decreases with increasing SSA, regardless of surface area. 2-D dopant contrast imaging of different textures with similar surface areas also indicates that the extent of doping is enhanced with increasing SSA. 3-D diffusion simulations of nanocones show that both the extent of radial doping within a texture feature and the metallurgical junction depth in the underlying substrate increase with increasing SSA. We suggest SSA should be considered more readily when studying B-Si and its integration into solar cells. Index Terms-Black silicon, phosphorus doping, silicon nanotexture, surface area, surface-to-volume ratio. I. INTRODUCTION N ANOTEXTURED silicon often falls under the collective label of black silicon (B-Si) which typically describes surfaces with low reflectance across a wide wavelength range (ultraviolet to near-infrared) and which appear black to the eye. B-Si can be prepared using a myriad of techniques and covers a wide range of surface morphologies and feature dimensions (from nano to micron-scale), including nanoporous layers [1],
Progress in Photovoltaics: Research and Applications, 2018
A common concern regarding plated contacts to solar cells is the adhesion strength. In this work,... more A common concern regarding plated contacts to solar cells is the adhesion strength. In this work, laser-formed anchor points have been applied to Suntech Power's PLUTO passivated emitter and rear cells. Voltages as high as 696 mV have been achieved, showing the ability of a laser-doped selective emitter at the front surface and localized contacts at the rear when combined with the hydrogenation of defects to reduce the device dark saturation current to well below current norms for commercial passivated emitter and rear cells. The simple hydrogen passivation process applied during sintering appears to facilitate the high voltages by significantly reducing recombination associated with the p-type Cz wafer and laser-induced defects formed during laser doping. The same hydrogenation process almost entirely eliminates the damage caused by laser ablation in forming the anchor points. With 50% anchor point coverage (more than necessary for adhesion equivalent to or stronger than screen-printed contacts), an average V OC of 693 mV was achieved, with an average current of 40.5 mA/cm 2 , average device efficiency of 20.2%, and a single best cell of 20.5% efficiency. These cells also exhibit excellent contact adhesion and pass all thermal cycling and damp-heat testing according to IEC 61215.
Solar Energy Materials and Solar Cells, 2019
In this work, we investigate the use of advanced hydrogenation and low-temperature diffusion proc... more In this work, we investigate the use of advanced hydrogenation and low-temperature diffusion processes (a 3 h 700°C process after emitter diffusion) for the electrical neutralization of laser-induced defects for laser doped and grooved solar cells. Despite the laser doping and grooving (LDG) process being performed before silicon nitride passivation to avoid thermal expansion mismatch between the silicon and the silicon nitride layer, some crystallographic defects are still formed during the process. The application of a low-temperature diffusion process increases implied open circuit voltages by 14 mV, potentially due to phosphorus diffusion of dislocated regions induced during laser processing. Laser hydrogenation is shown to be capable of passivating the majority of the remaining laser-induced defects. Over 1% absolute improvement in efficiency is achieved on cells with a full area aluminum back surface field. Preliminary results with minimal optimization demonstrate efficiencies of over 19% with a full area Al back contact cell. The potential to achieve much higher voltages when used with a passivated rear is also demonstrated.
Japanese Journal of Applied Physics, 2017
We report on the progress for the understanding of carrier-induced degradation (CID) in p-type mo... more We report on the progress for the understanding of carrier-induced degradation (CID) in p-type mono and multi-crystalline silicon (mc-Si) solar cells, and methods of mitigation. Defect formation is a key aspect to mitigating CID. Illuminated annealing can be used for both mono and mc-Si solar cells to reduce CID. The latest results of an 8-s UNSW advanced hydrogenation process applied to industrial p-type Czochralski PERC solar cells are shown with average efficiency enhancements of 1.1% absolute from eight different solar cell manufacturers. Results from three new industrial CID mitigation tools are presented, reducing CID to 0.8-1.1% relative, compared to 4.2% relative on control cells. Similar advanced hydrogenation processes can also be applied to multi-crystalline silicon passivated emitter with rear local contact (PERC) cells, however to date, the processes take longer and are less effective. Modifications to the firing processes can also suppress CID in multi-crystalline cells during subsequent illumination. The most stable results are achieved with a multi-stage process consisting of a second firing process at a reduced firing temperature, followed by extended illuminated annealing.
Zhonghua liu xing bing xue za zhi = Zhonghua liuxingbingxue zazhi, Jan 10, 2018
To understand the acceptance and personal demand for cancer screening service among the urban res... more To understand the acceptance and personal demand for cancer screening service among the urban residents who had never been involved in any national level cancer screening programs in China and identify the key factors influencing the sustainability of cancer screening. A questionnaire survey was conducted among the local people aged 40-69 years selected through convenience sampling in 16 provinces of China to collect the general information about their demands for the screening service and others. A total of 16 394 qualified questionnaires were completed. The average age of the people surveyed was (53.8±8.0) years, and men accounted for 44.6%. Without concerning the cost, 4 831 people (29.5%) had no demands for cancer screening services, the reasons are as follow: they would like to go to see doctors only when they were ill (61.8%); they had already received similar medical examinations (36.8%) and they would like to receive cancer screening directly without pre-health risk assessme...
2016 IEEE 43rd Photovoltaic Specialists Conference (PVSC), 2016
The refractive index at 633 nm is often used to characterize silicon nitride films. Besides provi... more The refractive index at 633 nm is often used to characterize silicon nitride films. Besides providing information about the reflection at this particular wavelength, it is frequently used to indicate additional information regarding the film's absorption and even regarding its surface passivation quality. In this study, we compare nine different silicon nitride films, all with a similar refractive index at 633 nm (2.09±0.01). We demonstrate that these films exhibit very different electrical, chemical and optical properties despite their similar refractive index values. As a result of this investigation, we have developed industrial low-absorption silicon nitride films that provide excellent surface passivation, with saturation current density of 7 fA/cm2 on both n- and p-type wafers. This surface passivation quality is equal to that obtained by industrial silicon-rich silicon nitride films. All the films developed in this study were fabricated using industrial equipment and are thermally stable.
2016 IEEE 43rd Photovoltaic Specialists Conference (PVSC), 2016
Copper plated contacts have the potential to become the dominant front metallization technology o... more Copper plated contacts have the potential to become the dominant front metallization technology over silver contacts if several key issues can be solved. These are addressed in this work. Through large batches of cells produced at Suntech on Pluto's 0.5 GW production line, it is shown that: adhesion concerns can be over come by optimized nickel seed layers or laser formed anchor points; long-term reliability can also be solved by an optimized nickel seed layer in conjunction with deep laser doping; and an absence of large-scale high-throughput in-line plating equipment is no longer an issue. Average device efficiencies are 19–20% for Al-BSF and over 20% for PERC structures with record open circuit voltages but with a small efficiency loss when anchor points are applied.
Energy Procedia, 2015
Advanced hydrogenation processes targeting the generation of neutrally charged hydrogen (H 0) are... more Advanced hydrogenation processes targeting the generation of neutrally charged hydrogen (H 0) are applied to passivate structural defects in seeded-cast quasi mono-crystalline silicon wafers and boron-oxygen defects in Czochralski silicon. The application of a one minute laser hydrogenation process onto a finished screen printed solar cell fabricated on the dislocation-rich seeded-cast material resulted in efficiency enhancements of 0.6% absolute through improvements in the implied open circuit voltage and internal quantum efficiency in the vicinity of the dislocated regions. A new insight is presented on the formation of boron-oxygen defects with a strong dependence on illumination intensity. An advanced laser hydrogenation process is presented to rapidly form and hydrogenate boron-oxygen defects simultaneously, in an 8 s process applied directly after belt furnace firing, with the hydrogenation of more than 95% of boron-oxygen defects at a peak temperature of approximately 360 °C on lifetime test structures. The same 8 s process is also demonstrated on standard screen-printed solar cells applied directly after belt furnace firing to simultaneously form-and hydrogenate the boron-oxygen defects, with no subsequent loss in electrical performance, hence avoiding a 0.7% absolute loss in efficiency due to light-induced degradation.
International Journal of Photoenergy, 2015
The application of lasers to enable advanced hydrogenation processes with charge state control is... more The application of lasers to enable advanced hydrogenation processes with charge state control is explored. Localised hydrogenation is realised through the use of lasers to achieve localised illumination and heating of the silicon material and hence spatially control the hydrogenation process. Improvements in minority carrier lifetime are confirmed in the laser hydrogenated regions using photoluminescence (PL) imaging. However with inappropriate laser settings a localised reduction in minority carrier lifetime can result. It is observed that high illumination intensities and rapid cooling are beneficial for achieving improvements in minority carrier lifetimes through laser hydrogenation. The laser hydrogenation process is then applied to finished screen-printed solar cells fabricated on seeded-cast quasi monocrystalline silicon wafers. The passivation of dislocation clusters is observed with clear improvements in quantum efficiency, open circuit voltage, and short circuit current de...
2014 IEEE 40th Photovoltaic Specialist Conference (PVSC), 2014
The formation of heavily doped p<sup>+</sup> region on p-type silicon substrates usin... more The formation of heavily doped p<sup>+</sup> region on p-type silicon substrates using laser doping through a layer of ALD AlO<sub>x</sub> is studied. A 532 nm continuous wave (CW) laser is used to incorporate Al atoms from the AlO<sub>x</sub> layers to form p<sup>+</sup> silicon. The p<sup>+</sup> regions formed through laser doping are found to be affected by various parameters such as laser speed and power. Sheet resistances as low as 10 Ω/□ were achieved using a power of 15 W and laser scanning speed of 0.5 m/s. The impact of the laser doping process on effective minority carrier lifetime is investigated using only the AlO<sub>x</sub> layer as a dopant source, as well as with the addition of a Boron dopant source. Laser doping boron have better protection by introducing a lifetime drop from 67 μs to 57.7 μs after laser doping comparing to the lifetime drop of laser doping AlO<sub>x</sub> from 62.5 μs to 46.1 μs. However, the addition of a boron spin on dopant source may induce voids in the laser doped region.
2012 38th IEEE Photovoltaic Specialists Conference, 2012
ABSTRACT The practical realization of high efficiency laser-doped semiconductor fingers (SCF) sil... more ABSTRACT The practical realization of high efficiency laser-doped semiconductor fingers (SCF) silicon solar cell is inhibited by high contact resistance. By plating the SCF with metal, a new SCF cell concept known as the “Advanced SCF” (AdvSCF) cell that can resolve the contact resistance problem is presented. In the first AdvSCF cells demonstrated in this work, the nickel (Ni) plating coverage across the cell was found to be non-uniform with Ni voids mostly concentrated around the busbar. This was found to be avoidable by ensuring that the spin-on phosphoric acid dopant layer was uniformly thick across the whole cell area and especially at the busbar. With uniform Ni plating coverage achieved, in a batch of 6 AdvSCF cells, an average batch efficiency of 18.40 % was achieved with the highest at 18.82 %. This was achieved without any experimental optimization of the front grid design or other cell properties, implying that there is potential to achieve significantly higher efficiency levels.
2011 37th IEEE Photovoltaic Specialists Conference, 2011
A record independently confirmed production cell efficiency of 19.3% is presented for a large-are... more A record independently confirmed production cell efficiency of 19.3% is presented for a large-area p-type Czochralski (CZ) silicon solar cell, based on the University of New South Wales (UNSW) laser-doped selective emitter technology. In this paper, the innovative and patented laser-doping technology is simply added to a standard Centrotherm turnkey line, operating with a modified process and the addition of the laser-doping and light-induced plating steps. Impressively, this record efficiency is achieved by using standard commercial grade p-type CZ-grown silicon wafers on standard production equipment and exceeds the previous independently confirmed record for any technology of 19.2% using a standard aluminum back-surface field with full rear coverage. The avoidance of laser-induced defects is discussed in this paper to overcome previous limitations of the laser-doping technology using conventional Q-switched lasers or the laser chemical processing method. It is demonstrated that the use of appropriate lasers can avoid defect formation through thermal cycling while still allowing for the sufficient mixing of dopants and allow laser doping to be performed through a standard SiN layer with contacts formed through a self-aligning metallization scheme.
2009 34th IEEE Photovoltaic Specialists Conference (PVSC), 2009
Page 1. REAR JUNCTION LASER DOPED SOLAR CELLS ON CZ N-TYPE SILICON Ly Mai, Ziv Hameiri, Budi s.Tj... more Page 1. REAR JUNCTION LASER DOPED SOLAR CELLS ON CZ N-TYPE SILICON Ly Mai, Ziv Hameiri, Budi s.Tjahjono, Stuart R. Wenham, Adeline Sugianto, Matt B.Edwards ARC Photovoltaics Centre of Excellence The University ...
Solar Energy Materials and Solar Cells, 2009
N-type silicon wafers have been found to offer numerous advantages over p-type silicon wafers, su... more N-type silicon wafers have been found to offer numerous advantages over p-type silicon wafers, such that they are becoming more widely used for manufacturing high-efficiency commercial solar cells. This paper focuses on work done on n-type cell structures with a screen-printed aluminum-alloyed rear junction, laser-doped selective emitter and light-induced plated front contacts to suit large-scale commercial production. However, with such a cell structure we report unusual linear shunting behavior that is only present under illumination but disappears under dark conditions. It was shown that such a phenomenon can be represented by a phototransistor model. In fact, such shunting effects are found to have detrimental impacts on the cell short-circuit current density (J sc) and fill factor (FF), which limits the efficiency of cells in this work to 12%.
Solar Energy Materials and Solar Cells, 2012
ABSTRACT Effective self-aligned metallisation schemes, such as the electroless and light induced ... more ABSTRACT Effective self-aligned metallisation schemes, such as the electroless and light induced plating techniques have been well-characterised and used in photovoltaic devices for many decades. However, application of these plating techniques to standard acid-textured, phosphorus-diffused, p-type multi-crystalline silicon (Si) wafers with a plasma enhanced chemical vapour deposition (PECVD) silicon nitride (SiN x) coated surface can be problematic due to over-plating. In this paper, we identify the two main causes of over-plating on these wafers: the physical properties of the deposited SiN x layer and the topology of the acid-textured multi-crystalline wafer surfaces. It is shown that the implementation of an innovative acid rounding or alkali etch process prior to the PECVD process can eliminate over-plating problems and, thus, improve the performance of the final cell devices resulting in an average efficiency of 16.8% and an average fill factor (FF) of 78% for laser-doped selective emitter cells fabricated on commercial grade wafers with nominal resistivity of 1 O cm.
Custom-glazed terracotta tiles Application: Rain screen facade Properties of material: The terrac... more Custom-glazed terracotta tiles Application: Rain screen facade Properties of material: The terracotta material provides a ventilated and pressure-equalized enclosure that helps keep the building dry to reduce maintenance while also saving energy.
The use of Laser Doping technology to form a selective emitter on solar cells has proven to be si... more The use of Laser Doping technology to form a selective emitter on solar cells has proven to be simple, cost effective, and suitable for commercial production. Efficiencies in excess of 18% have consistently been demonstrated on industrial grade p-type CZ wafers. One of the most important aspects of the laser doping technology is to provide localised heavily doped regions without subjecting the entire wafer to high temperature processing. This feature facilitates its suitability for fabricating multicrystalline solar cells. Multicrystalline wafer material often degrades at high processing temperature. Nevertheless, there are still several challenges in adapting the laser doping concept to multicrystalline wafers, particularly due to the presence of grain boundaries. The front anti-reflection coating must not only allow the hydrogenation effect to take place in passivating the bulk material but also protect the wafers against laser induced defects and be sufficiently dense to act as a plating mask. In this work, double stack layers of silicon oxy-nitride and silicon nitride (SiNx) are used as anti-reflection coating for the front surface. The passivation effects of these stacked layers, along with its ability to withstand laser induced defects will be discussed in this paper. Reflection properties of the silicon oxy-nitride single layer and the silicon oxy-nitride/silicon nitride double stack layers antireflection coatings are examined.
In this paper, we report on the effect of different annealing processes on rear side AlOx/SiNx st... more In this paper, we report on the effect of different annealing processes on rear side AlOx/SiNx stack passivation and the effect of AlOx thickness on implied open circuit voltage (iVoc) loss during laser doping using the AlOx layer and an additionally applied boron spin-on-dopant layer as a dopant source. Thin layers of AlOx capped by SiNx show improved iVoc after thermal annealing with slightly higher values observed after a 700oC peak temperature firing process than a conventional 400oC anneal. For thicker layers, blistering is observed after the firing process resulting in substantially lower iVoc than wafers annealed at 400oC. The improved passivation provided by thinner layers annealed at 400 oC is attributed to more effective hydrogen diffusion into the bulk of the wafers. When laser doping through the AlOx layers, thick AlOx layers result in lower voltage loss; however, the iVoc value degrade upon subsequent annealing. On the other hand, thin AlOx layers show a substantial improvement upon the same annealing process.
IEEE Journal of Photovoltaics, 2021
The integration of nanotextured black silicon (B-Si) into solar cells is often complicated by its... more The integration of nanotextured black silicon (B-Si) into solar cells is often complicated by its enhanced phosphorus doping effect, which is typically attributed to increased surface area. In this article, we show that B-Si's surface-to-volume ratio, or specific surface area (SSA), which is directly related to surface reactivity, is a better indicator of reduced sheet resistance. We investigate six B-Si conditions with varying dimensions based on two morphology types prepared using metal-catalyzed chemical etching and reactive-ion etching. We demonstrate that for a POCl 3 diffusion, B-Si sheet resistance decreases with increasing SSA, regardless of surface area. 2-D dopant contrast imaging of different textures with similar surface areas also indicates that the extent of doping is enhanced with increasing SSA. 3-D diffusion simulations of nanocones show that both the extent of radial doping within a texture feature and the metallurgical junction depth in the underlying substrate increase with increasing SSA. We suggest SSA should be considered more readily when studying B-Si and its integration into solar cells. Index Terms-Black silicon, phosphorus doping, silicon nanotexture, surface area, surface-to-volume ratio. I. INTRODUCTION N ANOTEXTURED silicon often falls under the collective label of black silicon (B-Si) which typically describes surfaces with low reflectance across a wide wavelength range (ultraviolet to near-infrared) and which appear black to the eye. B-Si can be prepared using a myriad of techniques and covers a wide range of surface morphologies and feature dimensions (from nano to micron-scale), including nanoporous layers [1],
Progress in Photovoltaics: Research and Applications, 2018
A common concern regarding plated contacts to solar cells is the adhesion strength. In this work,... more A common concern regarding plated contacts to solar cells is the adhesion strength. In this work, laser-formed anchor points have been applied to Suntech Power's PLUTO passivated emitter and rear cells. Voltages as high as 696 mV have been achieved, showing the ability of a laser-doped selective emitter at the front surface and localized contacts at the rear when combined with the hydrogenation of defects to reduce the device dark saturation current to well below current norms for commercial passivated emitter and rear cells. The simple hydrogen passivation process applied during sintering appears to facilitate the high voltages by significantly reducing recombination associated with the p-type Cz wafer and laser-induced defects formed during laser doping. The same hydrogenation process almost entirely eliminates the damage caused by laser ablation in forming the anchor points. With 50% anchor point coverage (more than necessary for adhesion equivalent to or stronger than screen-printed contacts), an average V OC of 693 mV was achieved, with an average current of 40.5 mA/cm 2 , average device efficiency of 20.2%, and a single best cell of 20.5% efficiency. These cells also exhibit excellent contact adhesion and pass all thermal cycling and damp-heat testing according to IEC 61215.
Solar Energy Materials and Solar Cells, 2019
In this work, we investigate the use of advanced hydrogenation and low-temperature diffusion proc... more In this work, we investigate the use of advanced hydrogenation and low-temperature diffusion processes (a 3 h 700°C process after emitter diffusion) for the electrical neutralization of laser-induced defects for laser doped and grooved solar cells. Despite the laser doping and grooving (LDG) process being performed before silicon nitride passivation to avoid thermal expansion mismatch between the silicon and the silicon nitride layer, some crystallographic defects are still formed during the process. The application of a low-temperature diffusion process increases implied open circuit voltages by 14 mV, potentially due to phosphorus diffusion of dislocated regions induced during laser processing. Laser hydrogenation is shown to be capable of passivating the majority of the remaining laser-induced defects. Over 1% absolute improvement in efficiency is achieved on cells with a full area aluminum back surface field. Preliminary results with minimal optimization demonstrate efficiencies of over 19% with a full area Al back contact cell. The potential to achieve much higher voltages when used with a passivated rear is also demonstrated.
Japanese Journal of Applied Physics, 2017
We report on the progress for the understanding of carrier-induced degradation (CID) in p-type mo... more We report on the progress for the understanding of carrier-induced degradation (CID) in p-type mono and multi-crystalline silicon (mc-Si) solar cells, and methods of mitigation. Defect formation is a key aspect to mitigating CID. Illuminated annealing can be used for both mono and mc-Si solar cells to reduce CID. The latest results of an 8-s UNSW advanced hydrogenation process applied to industrial p-type Czochralski PERC solar cells are shown with average efficiency enhancements of 1.1% absolute from eight different solar cell manufacturers. Results from three new industrial CID mitigation tools are presented, reducing CID to 0.8-1.1% relative, compared to 4.2% relative on control cells. Similar advanced hydrogenation processes can also be applied to multi-crystalline silicon passivated emitter with rear local contact (PERC) cells, however to date, the processes take longer and are less effective. Modifications to the firing processes can also suppress CID in multi-crystalline cells during subsequent illumination. The most stable results are achieved with a multi-stage process consisting of a second firing process at a reduced firing temperature, followed by extended illuminated annealing.
Zhonghua liu xing bing xue za zhi = Zhonghua liuxingbingxue zazhi, Jan 10, 2018
To understand the acceptance and personal demand for cancer screening service among the urban res... more To understand the acceptance and personal demand for cancer screening service among the urban residents who had never been involved in any national level cancer screening programs in China and identify the key factors influencing the sustainability of cancer screening. A questionnaire survey was conducted among the local people aged 40-69 years selected through convenience sampling in 16 provinces of China to collect the general information about their demands for the screening service and others. A total of 16 394 qualified questionnaires were completed. The average age of the people surveyed was (53.8±8.0) years, and men accounted for 44.6%. Without concerning the cost, 4 831 people (29.5%) had no demands for cancer screening services, the reasons are as follow: they would like to go to see doctors only when they were ill (61.8%); they had already received similar medical examinations (36.8%) and they would like to receive cancer screening directly without pre-health risk assessme...
2016 IEEE 43rd Photovoltaic Specialists Conference (PVSC), 2016
The refractive index at 633 nm is often used to characterize silicon nitride films. Besides provi... more The refractive index at 633 nm is often used to characterize silicon nitride films. Besides providing information about the reflection at this particular wavelength, it is frequently used to indicate additional information regarding the film's absorption and even regarding its surface passivation quality. In this study, we compare nine different silicon nitride films, all with a similar refractive index at 633 nm (2.09±0.01). We demonstrate that these films exhibit very different electrical, chemical and optical properties despite their similar refractive index values. As a result of this investigation, we have developed industrial low-absorption silicon nitride films that provide excellent surface passivation, with saturation current density of 7 fA/cm2 on both n- and p-type wafers. This surface passivation quality is equal to that obtained by industrial silicon-rich silicon nitride films. All the films developed in this study were fabricated using industrial equipment and are thermally stable.
2016 IEEE 43rd Photovoltaic Specialists Conference (PVSC), 2016
Copper plated contacts have the potential to become the dominant front metallization technology o... more Copper plated contacts have the potential to become the dominant front metallization technology over silver contacts if several key issues can be solved. These are addressed in this work. Through large batches of cells produced at Suntech on Pluto's 0.5 GW production line, it is shown that: adhesion concerns can be over come by optimized nickel seed layers or laser formed anchor points; long-term reliability can also be solved by an optimized nickel seed layer in conjunction with deep laser doping; and an absence of large-scale high-throughput in-line plating equipment is no longer an issue. Average device efficiencies are 19–20% for Al-BSF and over 20% for PERC structures with record open circuit voltages but with a small efficiency loss when anchor points are applied.
Energy Procedia, 2015
Advanced hydrogenation processes targeting the generation of neutrally charged hydrogen (H 0) are... more Advanced hydrogenation processes targeting the generation of neutrally charged hydrogen (H 0) are applied to passivate structural defects in seeded-cast quasi mono-crystalline silicon wafers and boron-oxygen defects in Czochralski silicon. The application of a one minute laser hydrogenation process onto a finished screen printed solar cell fabricated on the dislocation-rich seeded-cast material resulted in efficiency enhancements of 0.6% absolute through improvements in the implied open circuit voltage and internal quantum efficiency in the vicinity of the dislocated regions. A new insight is presented on the formation of boron-oxygen defects with a strong dependence on illumination intensity. An advanced laser hydrogenation process is presented to rapidly form and hydrogenate boron-oxygen defects simultaneously, in an 8 s process applied directly after belt furnace firing, with the hydrogenation of more than 95% of boron-oxygen defects at a peak temperature of approximately 360 °C on lifetime test structures. The same 8 s process is also demonstrated on standard screen-printed solar cells applied directly after belt furnace firing to simultaneously form-and hydrogenate the boron-oxygen defects, with no subsequent loss in electrical performance, hence avoiding a 0.7% absolute loss in efficiency due to light-induced degradation.
International Journal of Photoenergy, 2015
The application of lasers to enable advanced hydrogenation processes with charge state control is... more The application of lasers to enable advanced hydrogenation processes with charge state control is explored. Localised hydrogenation is realised through the use of lasers to achieve localised illumination and heating of the silicon material and hence spatially control the hydrogenation process. Improvements in minority carrier lifetime are confirmed in the laser hydrogenated regions using photoluminescence (PL) imaging. However with inappropriate laser settings a localised reduction in minority carrier lifetime can result. It is observed that high illumination intensities and rapid cooling are beneficial for achieving improvements in minority carrier lifetimes through laser hydrogenation. The laser hydrogenation process is then applied to finished screen-printed solar cells fabricated on seeded-cast quasi monocrystalline silicon wafers. The passivation of dislocation clusters is observed with clear improvements in quantum efficiency, open circuit voltage, and short circuit current de...
2014 IEEE 40th Photovoltaic Specialist Conference (PVSC), 2014
The formation of heavily doped p<sup>+</sup> region on p-type silicon substrates usin... more The formation of heavily doped p<sup>+</sup> region on p-type silicon substrates using laser doping through a layer of ALD AlO<sub>x</sub> is studied. A 532 nm continuous wave (CW) laser is used to incorporate Al atoms from the AlO<sub>x</sub> layers to form p<sup>+</sup> silicon. The p<sup>+</sup> regions formed through laser doping are found to be affected by various parameters such as laser speed and power. Sheet resistances as low as 10 Ω/□ were achieved using a power of 15 W and laser scanning speed of 0.5 m/s. The impact of the laser doping process on effective minority carrier lifetime is investigated using only the AlO<sub>x</sub> layer as a dopant source, as well as with the addition of a Boron dopant source. Laser doping boron have better protection by introducing a lifetime drop from 67 μs to 57.7 μs after laser doping comparing to the lifetime drop of laser doping AlO<sub>x</sub> from 62.5 μs to 46.1 μs. However, the addition of a boron spin on dopant source may induce voids in the laser doped region.
2012 38th IEEE Photovoltaic Specialists Conference, 2012
ABSTRACT The practical realization of high efficiency laser-doped semiconductor fingers (SCF) sil... more ABSTRACT The practical realization of high efficiency laser-doped semiconductor fingers (SCF) silicon solar cell is inhibited by high contact resistance. By plating the SCF with metal, a new SCF cell concept known as the “Advanced SCF” (AdvSCF) cell that can resolve the contact resistance problem is presented. In the first AdvSCF cells demonstrated in this work, the nickel (Ni) plating coverage across the cell was found to be non-uniform with Ni voids mostly concentrated around the busbar. This was found to be avoidable by ensuring that the spin-on phosphoric acid dopant layer was uniformly thick across the whole cell area and especially at the busbar. With uniform Ni plating coverage achieved, in a batch of 6 AdvSCF cells, an average batch efficiency of 18.40 % was achieved with the highest at 18.82 %. This was achieved without any experimental optimization of the front grid design or other cell properties, implying that there is potential to achieve significantly higher efficiency levels.
2011 37th IEEE Photovoltaic Specialists Conference, 2011
A record independently confirmed production cell efficiency of 19.3% is presented for a large-are... more A record independently confirmed production cell efficiency of 19.3% is presented for a large-area p-type Czochralski (CZ) silicon solar cell, based on the University of New South Wales (UNSW) laser-doped selective emitter technology. In this paper, the innovative and patented laser-doping technology is simply added to a standard Centrotherm turnkey line, operating with a modified process and the addition of the laser-doping and light-induced plating steps. Impressively, this record efficiency is achieved by using standard commercial grade p-type CZ-grown silicon wafers on standard production equipment and exceeds the previous independently confirmed record for any technology of 19.2% using a standard aluminum back-surface field with full rear coverage. The avoidance of laser-induced defects is discussed in this paper to overcome previous limitations of the laser-doping technology using conventional Q-switched lasers or the laser chemical processing method. It is demonstrated that the use of appropriate lasers can avoid defect formation through thermal cycling while still allowing for the sufficient mixing of dopants and allow laser doping to be performed through a standard SiN layer with contacts formed through a self-aligning metallization scheme.
2009 34th IEEE Photovoltaic Specialists Conference (PVSC), 2009
Page 1. REAR JUNCTION LASER DOPED SOLAR CELLS ON CZ N-TYPE SILICON Ly Mai, Ziv Hameiri, Budi s.Tj... more Page 1. REAR JUNCTION LASER DOPED SOLAR CELLS ON CZ N-TYPE SILICON Ly Mai, Ziv Hameiri, Budi s.Tjahjono, Stuart R. Wenham, Adeline Sugianto, Matt B.Edwards ARC Photovoltaics Centre of Excellence The University ...
Solar Energy Materials and Solar Cells, 2009
N-type silicon wafers have been found to offer numerous advantages over p-type silicon wafers, su... more N-type silicon wafers have been found to offer numerous advantages over p-type silicon wafers, such that they are becoming more widely used for manufacturing high-efficiency commercial solar cells. This paper focuses on work done on n-type cell structures with a screen-printed aluminum-alloyed rear junction, laser-doped selective emitter and light-induced plated front contacts to suit large-scale commercial production. However, with such a cell structure we report unusual linear shunting behavior that is only present under illumination but disappears under dark conditions. It was shown that such a phenomenon can be represented by a phototransistor model. In fact, such shunting effects are found to have detrimental impacts on the cell short-circuit current density (J sc) and fill factor (FF), which limits the efficiency of cells in this work to 12%.
Solar Energy Materials and Solar Cells, 2012
ABSTRACT Effective self-aligned metallisation schemes, such as the electroless and light induced ... more ABSTRACT Effective self-aligned metallisation schemes, such as the electroless and light induced plating techniques have been well-characterised and used in photovoltaic devices for many decades. However, application of these plating techniques to standard acid-textured, phosphorus-diffused, p-type multi-crystalline silicon (Si) wafers with a plasma enhanced chemical vapour deposition (PECVD) silicon nitride (SiN x) coated surface can be problematic due to over-plating. In this paper, we identify the two main causes of over-plating on these wafers: the physical properties of the deposited SiN x layer and the topology of the acid-textured multi-crystalline wafer surfaces. It is shown that the implementation of an innovative acid rounding or alkali etch process prior to the PECVD process can eliminate over-plating problems and, thus, improve the performance of the final cell devices resulting in an average efficiency of 16.8% and an average fill factor (FF) of 78% for laser-doped selective emitter cells fabricated on commercial grade wafers with nominal resistivity of 1 O cm.