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Author: Publisher: ISBN: Category : Polycrystals Languages : en Pages : 171
Book Description
The research focused on the process study for deposition of device quality polycrystalline silicon (poly-Si) thin films and solar cell fabrication by using a novel technique, metal-induced growth (MIG). Cobalt (Co) is introduced in the studies as a seed layer metal for the first time, while nickel (Ni) was another candidate. To grow the poly-Si, Co or Ni seed-layers were deposited on the foreign substrates by thermal evaporation with a few nm to 50 nm thickness. Substrates were transferred into the sputtering system for Si sputtering at elevated temperature from 525°C to 625°C. The Co or Ni reacted with sputtered Si to form metal disilicides which have very small lattice mismatch with Si (0.4% lattice mismatch for NiSi2 and Si, 1.2% lattice mismatch for CoSi2 and Si). The crystalline metal disilicides provide nucleation sites for poly-Si growth. With metal-induced growth, the relatively large-grain poly-Si films can be produced at relatively low temperatures on the various foreign substrates. Compared with Ni induced Si films, Co induced poly-Si has longer minority lifetime of 0.46 [mu]s as deposited and 1.3 [mu]s after annealing. A two-step sputtering method used for film deposition showed superiority over single step sputtering by achieving Si films with larger grain size (over 1 [mu]m) and less contamination. A double seed layer (5nm Co/50nm Ni) method was developed to produce the Si film with less Ni diffusion into Si. Metal-induced Si films were deposited on flexible thin tungsten substrates for solar cell fabrication. The good back Ohmic contact (metal disilicide) was formed naturally when the Si film was deposited. In this work, the solar cells were fabricated successfully by using metal-induced grown poly-Si. With the fabricated Schottky and P/N junction solar cells, the metal-induced growth processing parameters were studied. It was found that low-pressure sputtering, oxygen control during film growth, post-annealing and Si film hydrogenation are important to produce high quality poly-Si with fewer defects. The Schottky solar cell with optimized processing parameters showed the J[sub]sc and V[sub]oc of 12 mA/cm2 and 0.2 V, respectively. By passivating the MIG [mu]c-Si surface with hydrogenated nanocrystalline Si (nc-Si:H), the V[sub]oc was improved to 0.31 V. In addition, the current transport mechanism in Schottky and P/N junction devices were studied for different film growth conditions. The results showed that two-step sputtering, oxygen control and hydrogenation improved the quality of the Si film and devices.
Author: Publisher: ISBN: Category : Polycrystals Languages : en Pages : 171
Book Description
The research focused on the process study for deposition of device quality polycrystalline silicon (poly-Si) thin films and solar cell fabrication by using a novel technique, metal-induced growth (MIG). Cobalt (Co) is introduced in the studies as a seed layer metal for the first time, while nickel (Ni) was another candidate. To grow the poly-Si, Co or Ni seed-layers were deposited on the foreign substrates by thermal evaporation with a few nm to 50 nm thickness. Substrates were transferred into the sputtering system for Si sputtering at elevated temperature from 525°C to 625°C. The Co or Ni reacted with sputtered Si to form metal disilicides which have very small lattice mismatch with Si (0.4% lattice mismatch for NiSi2 and Si, 1.2% lattice mismatch for CoSi2 and Si). The crystalline metal disilicides provide nucleation sites for poly-Si growth. With metal-induced growth, the relatively large-grain poly-Si films can be produced at relatively low temperatures on the various foreign substrates. Compared with Ni induced Si films, Co induced poly-Si has longer minority lifetime of 0.46 [mu]s as deposited and 1.3 [mu]s after annealing. A two-step sputtering method used for film deposition showed superiority over single step sputtering by achieving Si films with larger grain size (over 1 [mu]m) and less contamination. A double seed layer (5nm Co/50nm Ni) method was developed to produce the Si film with less Ni diffusion into Si. Metal-induced Si films were deposited on flexible thin tungsten substrates for solar cell fabrication. The good back Ohmic contact (metal disilicide) was formed naturally when the Si film was deposited. In this work, the solar cells were fabricated successfully by using metal-induced grown poly-Si. With the fabricated Schottky and P/N junction solar cells, the metal-induced growth processing parameters were studied. It was found that low-pressure sputtering, oxygen control during film growth, post-annealing and Si film hydrogenation are important to produce high quality poly-Si with fewer defects. The Schottky solar cell with optimized processing parameters showed the J[sub]sc and V[sub]oc of 12 mA/cm2 and 0.2 V, respectively. By passivating the MIG [mu]c-Si surface with hydrogenated nanocrystalline Si (nc-Si:H), the V[sub]oc was improved to 0.31 V. In addition, the current transport mechanism in Schottky and P/N junction devices were studied for different film growth conditions. The results showed that two-step sputtering, oxygen control and hydrogenation improved the quality of the Si film and devices.
Author: Ruud E.I. Schropp Publisher: Springer ISBN: 1461556317 Category : Technology & Engineering Languages : en Pages : 215
Book Description
Amorphous silicon solar cell technology has evolved considerably since the first amorphous silicon solar cells were made at RCA Laboratories in 1974. Scien tists working in a number of laboratories worldwide have developed improved alloys based on hydrogenated amorphous silicon and microcrystalline silicon. Other scientists have developed new methods for growing these thin films while yet others have developed new photovoltaic (PV) device structures with im proved conversion efficiencies. In the last two years, several companies have constructed multi-megawatt manufacturing plants that can produce large-area, multijunction amorphous silicon PV modules. A growing number of people be lieve that thin-film photovoltaics will be integrated into buildings on a large scale in the next few decades and will be able to make a major contribution to the world's energy needs. In this book, Ruud E. I. Schropp and Miro Zeman provide an authoritative overview of the current status of thin film solar cells based on amorphous and microcrystalline silicon. They review the significant developments that have occurred during the evolution of the technology and also discuss the most im portant recent innovations in the deposition of the materials, the understanding of the physics, and the fabrication and modeling of the devices.
Author: Publisher: ISBN: Category : Languages : en Pages : 15
Book Description
Thin film silicon has many useful purposes. Among the applications are solar cells and thin film transistors. This project involves a new and potentially lower cost method to produce thin silicon films. The method is called metal induced growth (MIG). A thin catalyst metal layer deposited on a foreign low cost substrate serves as the basis for growth of a nanocrystalline silicon thin film with thickness of 5-10 microns and preferred orientation of (220). The silicon deposition by magnetron sputtering on the heated substrate resulted in columnar structured grains having a diameter up to about 0.5 microns. Schottky barrier solar cells fabricated on these films gave a photocurrent of about 5 mA/sq cm and open circuit voltage of 0.25 volts. A modified process gave NiSi crystalline nanowires with length up to 10 microns and diameter of about 50 nm.
Author: Deren Yang Publisher: Springer ISBN: 9783662564714 Category : Technology & Engineering Languages : en Pages : 0
Book Description
The utilization of sun light is one of the hottest topics in sustainable energy research. To efficiently convert sun power into a reliable energy – electricity – for consumption and storage, silicon and its derivatives have been widely studied and applied in solar cell systems. This handbook covers the photovoltaics of silicon materials and devices, providing a comprehensive summary of the state of the art of photovoltaic silicon sciences and technologies. This work is divided into various areas including but not limited to fundamental principles, design methodologies, wafering techniques/fabrications, characterizations, applications, current research trends and challenges. It offers the most updated and self-explanatory reference to all levels of students and acts as a quick reference to the experts from the fields of chemistry, material science, physics, chemical engineering, electrical engineering, solar energy, etc..
Author: Materials Research Society. Meeting Publisher: ISBN: Category : Technology & Engineering Languages : en Pages : 776
Book Description
This book celebrates 20 years of MRS symposia on the topic of amorphous silicon. Contributors showed that the simplified theories developed to explain the limited experimental information available in the early eighties have spurred more sophisticated experimentation - either refining the early understanding or making it irrelevant. The differences of opinion that continue to exist and emerge are probably the hallmark of the amazing vitality of this field. Applications range from 'mature' thin-film transistors, solar cells and image sensors, to the 'emerging' possibility of erbium-doped nanocrystalline silicon-based materials for lasers and amorphous silicon quantum dots for luminescent devices. The book discusses material characterization, growth processes and devices. Each chapter is further subdivided into sections that group papers around common themes. Topics include: nanomaterials; electronic structure; metastable effects; understanding of growth processes; laser-induced crystallization; metal-induced crystallization; other growth techniques; newer devices; solar cells and thin-film transistors.
Author: W.R. Fahrner Publisher: Trans Tech Publications Ltd ISBN: 3038131024 Category : Technology & Engineering Languages : en Pages : 208
Book Description
The world of today must face up to two contradictory energy problems: on the one hand, there is the sharply growing consumer demand in countries such as China and India. On the other hand, natural resources are dwindling. Moreover, many of those countries which still possess substantial gas and oil supplies are politically unstable. As a result, renewable natural energy sources have received great attention. Among these, solar-cell technology is one of the most promising candidates. However, there still remains the problem of the manufacturing costs of such cells. Many attempts have been made to reduce the production costs of conventional solar cells (manufactured from monocrystalline silicon using diffusion methods) by instead using cheaper grades of silicon, and simpler pn-junction fabrication. That is the hero of this book; the heterojunction solar cell.
Author: Eric S. Kozarsky Publisher: ISBN: Category : Languages : en Pages : 184
Book Description
The metal induced growth (MIG) process has been explored as an approach to producing microcrystalline Si at reduced temperatures. In this study, Pd was explored as an alternative catalyst for the MIG process. The process was optimized in order to maximize the photovoltaic response without raising the temperature too far above 600ʻC. Optimal conditions were found by depositing a 5 & mu;m thick Si film at a temperature of 625ʻC with subsequent annealing at 700ʻC for 2 hours in forming gas. The photo I-V measurements provided a JSC of 5. 39 mA/cm 2, a VOC of 245 mV, and a fill factor of 0. 447. Catalyst combinations were explored to combine Pd with other metals such as Cr, Co, and Ni. Initially, a device structure of Co/Ni/Pd was found to produce the best result. A later study found an improved stability with the removal of Ni from the device structure. This Co/Pd structure allowed for a reduction in deposition temperature to 575ʻC without sacrificing performance or stability. An annealing study was performed on these devices. It was found that the optimal condition for these devices involved annealing at 800ʻC for 12 hours. As this time is too extensive, annealing at 800ʻC for 2 hours was chosen as an alternative which sacrifices very little in terms of performance. A new process known as metal induced lateral growth (MILG) was introduced. This process utilized adjacent metal pads to laterally crystallize Si which is deposited on the sample. This metal free microcrystalline region allows for additional approaches to analysis and applications. Contacts were preserved prior to Si deposition allowing for easy analysis. As these bulk measurements produced inconsistent results, an alternative process was developed. The alternative process involved patterning much smaller catalyst pads followed by the MILG process. A secondary alignment process allowed for a top contact to be deposited. The top contacts allowed electrical measurements to be performed across metal free small gaps. This offered improved electrical measurements using the transmission line model. This process was extended into the area of thin film transistors. For this purpose, the source and drain metals are deposited and Si is deposited and crystallized in-situ. A secondary patterning deposits the source and drain contacts followed by gate oxide and gate metal depositions. Unfortunately, these devices suffer from large leakage currents which limit saturation. The field effect mobility was found to be between 0. 3-0. 6 cm 2 Vs. This low field effect mobility is primarily due to the MILG/MILG grain boundary present in the center of the channel. A final study involves the formation of a heterojunction device using Al doped ZnO deposited on top of the MIG Si. A buffer layer of SiO 2 was introduced between the Al-ZnO and the MIG Si. Simulations suggest this device without the buffer layer can achieve a potential JSC of 20. 79 mA/cm 2, a VOC 670 mV, and an efficiency of 11. 675%. Although the fabricated device showed good rectification, the SiO 2 buffer layer proved to be too thick and blocked any photovoltaic response.
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Author: Ruud E.I. Schropp
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Author: Shubhranshu Verma
Author: Elena A. Guliants
Author: Deren Yang
Author: Materials Research Society. Meeting
Author: W.R. Fahrner
Author: Sandra Schicho
Author: Eric S. Kozarsky