Surface Passivation of Industrial Crystalline Silicon Solar Cells
Surface passivation of silicon solar cells describes a technology for preventing electrons and holes to recombine prematurely with one another on the wafer surface. It increases the cell's energy conversion efficiencies and thus reduces the cost per kWh generated by a PV system. In the past few years, new tools have been developed to ensure low cost of ownership for high volume production of passivated silicon solar cells. Different deposition techniques (ALD, PECVD, APCVD) and different materials (SiO2, Al2O3, Si3N4) have been tested during the development process of more than 10 years. Now, the silicon solar cell manufacturing industry is picking up the concept of rear side passivation. The next generation silicon solar cells in production will be the PERC (Passivated Emitter and Rear Cell) type using all the reported achievements including novel tool concepts and process technologies. This timely overview of silicon solar cell surface passivation, written by the leading experts in the field, is a key read for students and researchers working with silicon solar cells, as well as solar cell manufacturers.
Inspec keywords: passivation; solar cells; chemical vapour deposition; atomic layer deposition; elemental semiconductors; silicon compounds; silicon; plasma CVD; semiconductor growth; semiconductor industry
Other keywords: Si3N4; surface passivation; chemical vapour deposition; crystalline silicon solar cells; market aspects; industrial solar cells; atomic layer deposition; PECVD; Si; amorphous silicon nitride passivation
Subjects: General topics in manufacturing and production engineering; Thin film growth, structure, and epitaxy; Chemical vapour deposition; Solar cells and arrays; Vacuum deposition; Photoelectric conversion; solar cells and arrays; General electrical engineering topics; Surface treatment (semiconductor technology); Surface treatment and coating techniques; Vacuum deposition; Semiconductor industry; Surface treatment and degradation in semiconductor technology; Chemical vapour deposition; Monographs, and collections
- Book DOI: 10.1049/PBPO106E
- Chapter DOI: 10.1049/PBPO106E
- ISBN: 9781785612466
- e-ISBN: 9781785612473
- Page count: 284
- Format: PDF
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Front Matter
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1 Market position of PERC silicon solar cells
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Solar energy is a cornerstone of the future global sustainable energy system. The book chapter outlines how performance and energy yield increase will have to evolve concurrently to make PV a major electricity source and how PERC-technology is an important milestone in achieving this.
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2 Introduction to surface passivation of industrial crystalline silicon solar cells
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The book chapter shows that surface passivation technologies have played a crucial role in the development of industrial silicon solar cells over the past 40 years, and they will continue to do so in the future. The authors describe a variety of surface passivation techniques that will help to take industrial silicon solar cells to even greater heights, ensuring ongoing reductions of the levelized cost of electricity (LCOE) from PV systems and their global deployment on a massive scale.
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3 Material properties of AlOx for silicon surface passivation
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The author focuses on the surface passivation mechanism of Al2O3 and how it is related to its material properties. The chapter starts off with a short description of the fundamentals of surface recombination stressing the importance of the electronic properties of the c-Si/Al2O3 interface with respect to defect density and fixed charge. Next, an overview is presented of the electronic properties for Al2O3 layers synthesised on c-Si substrates by various techniques. Finally, these electronic properties are related to the atomic-scale material properties for Al2O3 films with a particular focus on the, typically unintentional, presence of an interfacial silicon oxide film.
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4 Material properties of Al2O3 grown on Si: interface trap density (Dit) and fixed charge density (Qf)
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Chapter 4 gives a summary based on one of the authors' earlier articles (Vermang (2012)), and consistent with more general overview papers. First, Section 4.1 describes recombination at Si surfaces theoretically to clarify two key passivation approaches: chemical and field effect passivation. Then, Section 4.2 quantifies the chemical and field effect passivation of Al2O3, i.e., its interface trap density and fixed charge density, respectively. Finally, Section 4.3 provides a larger picture by comparing Al2O3 to other Si surface layers, and showing that Al2O3 surface passivation can also be applied to passivate thin film photovoltaics.
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5 PECVD-AlOx
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The authors review developments in the use of PECVD in the growth of AlOx layers for solar cells. They consider the microwave PECVD and inductively coupled plasma PECVD methods, and the characteristics of layers grown by the 2 techniques, Si surface passivation, and solar cell applications.
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6 Atmospheric pressure chemical vapor deposition of aluminum oxide for silicon surface passivation—background and materials science
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The author provides a general background on atmospheric pressure chemical vapor deposition (APCVD) of Al2O3, from its origins to more recent research, focusing on surface passivation applications for solar cells and the composition and structure of the APCVD Al2O3-Si interface.
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7 Al2O3 by atmospheric pressure chemical vapour deposition
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The author provides a historical review of research into the atmospheric pressure chemical vapour deposition (APCVD) of Al2O3 for silicon surface passivation in solar cell devices, considering deposition temperature influence on excess carrier lifetime, film thickness and interface state density.
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8 Surface passivation of industrial PERC solar cells
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In this book chapter, the authors summarize the main developments and improvements within the last 25 years which enabled the industrialization of the lab-type PERC solar cell concept. In particular, we describe the historic development and current status of key industrial PERC manufacturing process steps such as the rear passivation layer, typically applying an AlOx/SiNy layer stack, as well as the local Al rear contact formation by laser ablation, Al screen printing and subsequent firing. At the end of this chapter, an outlook is provided on future development opportunities such as further efficiency increases and bifacial PERC applications.
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9 Al2O3 passivation in industrial solar cells: n-PERT
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In this book chapter the properties of Al2O3 based p+ surface passivation is described, focusing on the impact of deposition conditions, annealing sequence, capping layer material, Al2O3 thickness, and surface morphology.
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10 Double-layer dielectric stacks for advanced surface passivation of crystalline silicon solar cells
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Surface passivation of moderately doped and heavily doped p-type surfaces is of major importance to both p-type and n-type solar cells. Considering the practical importance and relevance of p-type Si surfaces, i.e. a moderately doped (undiffused) p-type Si surface and a heavily doped p±-type Si surface, this chapter focuses on the investigation of surface passivation using double-layer dielectric stacks. We study a positively charged dielectric stack (i.e. SiOx capped with SiNx) as well as a negatively charged dielectric stack (i.e., AlOx capped with SiNx).
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11 Hydrogenated amorphous silicon nitride (a-SiNx:H) as surface passivation layer
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Over recent decades, surface-passivating properties of PECVD a-SiNx:H have been investigated extensively. These properties depend on the number of fixed charges (Qf) and interface density of states (Dit) and are in turn related to bulk and interface properties. In general, there is a positive correlation between Qf and Dit, which have opposite effects on the surface-passivating properties. For an optimal effective surface passivation, an optimization is therefore necessary. Higher Qf and Dit are found to correspond to a higher and deeper insertion of N in c-Si thereby increasing the concentration of these defects. This insertion is related to NH3 flow and temperature during plasma treatment. This technique for forming defect layers has been experimentally validated by EELS as well as high resolution TEM. MD simulation and ab initio DFT studies demonstrated the formation of defects and higher DOS in the bandgap for the same layer composition. Introduction of hydrogen was simulated with DFT as well and showed a lower DOS in the bandgap resulting in a better surface passivation. The effect of Qf at the interface on the passivating properties of a-SiNx:H applied to completed solar cells was proven as well and confirmed by PC1D device simulations.
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12 Microwave PE CVD reactor and process for industrial high throughput fabrication of aluminum oxide layers for solar cell applications
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This book chapter gives an overview of industrial microwave PE CVD reactors starting at details of the used linear plasma sources and showing then, that a system of modular equipment can be constructed, covering a wide range of wafer throughput and customized backside passivation layer systems.
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13 Spatial atomic layer deposition of A12O3: Levitrack, a one-pass ALD system with throughputs exceeding 6,000 wafers/h
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In this book chapter it is shown that Al2O3 deposition systems based on spatial ALD with wafer floatation are attractive for passivation of cSi solar cells in high-volume manufacturing. In principle, the throughput can be increased to 7,200 wafers/h; the limitation is not the ALD track, but the unloading automation.
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14 Spatial Al2O3 ALD: from Lab to Fab
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The book chapter reviews the process of spatial Al2O3 atomic layer deposition (ALD). Aspects covered include: time-based versus spatial methods; proof of principle spatial ALD; spatial ALD applications; from the proof of principle to InPassion® LAB; transform from Lab to Fab-InPassion® ALD; second generation-InPassion® ALD; combining the stack layers.
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Back Matter
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