Photovoltaic Manufacturing

1 Cover

2 Title Page

3 Copyright

4 Preface

5 1 Metal-Assisted Chemical Etching of Silicon: Origin, Mechanism, and Black Silicon Solar Cell Applications 1.1 Introduction 1.2 History and Mechanism of Metal-Assisted Chemical Etching of Silicon 1.3 Fabrication and Optical Properties of Black Silicon by MacEtch of Silicon 1.4 Photovoltaic Solar Cell Applications of MacEtch Black Silicon 1.5 Concluding Remarks Acknowledgements References

6 2 Alkaline Texturing 2.1 Introduction to Alkaline Texturing 2.2 Pyramid Formation 2.3 Chemical Mixtures Used in the Alkaline Texturing 2.4 Mechanisms of Alkaline Texturing, Important Parameters Involved in Alkaline Texturing 2.5 Surface Conditioning Prior to Alkaline Texturing 2.6 Problems Associated to Alkaline Texturing References

7 3 Advanced Texturing 3.1 Introduction to Advanced Texturing 3.2 History and Definition of Metal-Assisted Chemical Etching 3.3 Mechanisms of Metal-Assisted Chemical Etching 3.4 Methods of Metal-Assisted Chemical Etching 3.5 Copper-Assisted Chemical Etching 3.6 Conclusion References

8 4 Wet Chemical Cleaning for Industrial Application 4.1 Introduction 4.2 Status of Production Technology in Solar Cell Manufacturing 4.3 Wet Chemical Process Technology 4.4 Contamination Management 4.5 Cost Considerations 4.6 Conclusion Acknowledgments References

9 5 Analytical Techniques for Wet Processing 5.1 Introduction 5.2 Metal Analysis by ICP-MS 5.3 Determination of Organic Contaminations Acknowledgments References

10 Index

11 Also of Interest

12 End User License Agreement

1 Preface Figure 1 Conversion efficiencies of best research solar cells worldwide from 197... Figure 2 NREL chart of the highest confirmed conversion efficiencies for champio...

2 Chapter 1 Figure 1.1 SEM images of the silicon wafers with Au particles after DHF-H2O2 cle... Figure 1.2 (a) Schematical view of the experimental setup with an Au electrode o... Figure 1.3 (a) SEM image of aligned SiNW array prepared by one-step etching in H... Figure 1.4 (a, b) Schematics of metal-assisted etching of silicon in HF-H2O2 aqu... Figure 1.5 Energy band diagrams of energy band bending induced by H2O2 concentra... Figure 1.6 (a–d) SEM images showing the morphological evolution of a silicon waf... Figure 1.7 (a) Photograph of gold-catalyzed etched b-Si samples of different cry... Figure 1.8 (a–c) Top-view and cross-sectional (insets) SEM images of nanoporous ... Figure 1.9 (a) SEM image of SiNW-based single-crystalline b-Si by silver-catalyz... Figure 1.10 (a) Process sequence for texturization of mc-Si wafers by alkaline t... Figure 1.11 (a) SEM image of a conventional acid-textured MWSS mc-Si wafer. (b) ... Figure 1.12 SEM images of the inverted pyramid structures for (a) 10 min process...

3 Chapter 2Figure 2.1 Scanning electron microscopy (SEM) photograph of a textured surface.Figure 2.2 Location of the alkaline texturing within the entire process of a typ...Figure 2.3 Sequence of steps involved in the wet etching [6].Figure 2.4 SEM photograph of the stabilization at top and vertices of a pyramid ...Figure 2.5 Bond configuration of (a) (100), (b) (110), and (c) (111) planes [19]...Figure 2.6 Reaction mechanism involved in the first etching step of a (100) sili...Figure 2.7 Reaction mechanism involved in the second etching step of (100) silic...Figure 2.8 Micrographs of textured surfaces for 10 minutes in solutions containi...Figure 2.9 Reflectivity values at a wavelength of 725 nm, each dot means one waf...Figure 2.10 Contact angles (θ) between the liquid and the solid of two drops wit...Figure 2.11 Si etch rate increasing with NaOH content for a fresh and an aged so...Figure 2.12 Minimum reflectivity for a fresh and aged solution [74].Figure 2.13 SEM photograph of a Si surface with non-uniform size distribution of...Figure 2.14 SEM photograph showing the morphology of pyramids after 40 minutes o...Figure 2.15 The surface of a textured wafer with bubble spots highlighted.

4 Chapter 3Figure 3.1 Schematic of the potential relationship between bands in a Si substra...Figure 3.2 Schematic of the electrochemical processes involved in metal-assisted...Figure 3.3 Mechanism of hindering the lateral dissolution of Si along the pore d...Figure 3.4 Schematic of morphologies of etched structures (right column) induced...Figure 3.5 Scanning electron microscope images of Si nanostructures with polysty...Figure 3.6 Scanning electron microscope investigation of Si nanostructures induc...Figure 3.7 (a) Cross-sectional SEM image of Si (100) surface etched in HAuCl4 so...Figure 3.8 (a) Scanning electron microscope image of Ag nanoparticles on Si etch...Figure 3.9 Cross-sectional SEM images of p-Si (100) surfaces, after Ag is remove...Figure 3.10 Hemispheric total reflectance of the p-Si (100) wafer, after being e...Figure 3.11 Scanning electron microscope images of m-Si after etching in HF/AgNO...Figure 3.12 Hemispheric total reflectance of a m-Si wafer; unetched and after et...Figure 3.13 (a) Scanning electron microscope image of Cu nanoparticles deposited...Figure 3.14 Top-view and cross-sectional (insets) SEM images of Cu-nanoparticle ...Figure 3.15 Solar-spectrum-weighted reflectance (Rave) versus ρ = [HF]/([HF]+[H2...Figure 3.16 A photo of Cu nanoparticleassisted etching process and SEM images. (...Figure 3.17 Reflectance spectra of pyramid arrays and the inverted pyramid array...Figure 3.18 Scanning electron microscope image and schematics of Cu nanoparticle...

5 Chapter 4Figure 4.1 Average sales price reduction plotted against the cumulated PV module...Figure 4.2 Common process and rinsing baths for batch processing. (a) simple dip...Figure 4.3 Batch tool, on left side inlet for carriers. Robot arm with four carr...Figure 4.4 Inline tool, on left side automation for wafer placement on the lanes...Figure 4.5 Common process and rinsing for inline processing. Wafers are transpor...Figure 4.6 Relative costs for chemicals in a state-of-the-art wetbench, with a b...Figure 4.7 Typical state-of-the-art PERC process route with the wet chemical pro...Figure 4.8 General scheme of how wet processes are integrated into the solar cel...Figure 4.9 Summary of the relevant process steps centring on wafer cleaning. It ...Figure 4.10 Impact of cleaning efficiency measured via thermally oxidized p-type...Figure 4.11 Droplet sandwich etch (DSE) sampling method for the determination of...Figure 4.12 Column prepared for the analysis of the impact of the sawing process...Figure 4.13 Surface contamination of as-cut wafers. The numbers of the sampled w...Figure 4.14 Surface contamination before (squares) and after (circles) etching. ...Figure 4.15 In this figure, two cases are discriminated. Top: main source etchin...Figure 4.16 Enrichment simulation based on the observations of the main contamin...Figure 4.17 Surface contamination after alkaline texturing: of as-cut wafers (FE...Figure 4.18 Example for surface contamination of diamond-wire sawed Cz-wafers af...Figure 4.19 Metal contamination collected on wafer surfaces stored over time in ...Figure 4.20 Ion selective complexing agents used for the determination of Fe and...Figure 4.21 Calibration spectra of Fe (left) and Cu (right) in 2% HF [64].Figure 4.22 Correlation between surface contamination and implied Voc for PERC r...Figure 4.23 Carbon concentration per surface area, two pairs of measurement resu...Figure 4.24 Statistical model for the cleaning efficiency of different HF/O3 cle...Figure 4.25 Solar cell efficiencies on bifacial n-type solar cells (BiSoN). The ...Figure 4.26 Relative process related costs (derived from [72]). It takes into ac...Figure 4.27 Cost break-down of a wet chemical process tools. Thoughput of the to...

6 Chapter 5Figure 5.1 Left: As-cut wafer surface without visible defects. Right: The same w...Figure 5.2 SEM top view of wafer surface after alkaline texturing. Left: Referen...Figure 5.3 Comparison of relative signal intensities from ToF-SIMS surface spect...Figure 5.4 Limits of detection obtained from ICP-MS measurements comparing two m...Figure 5.5 Schematic representation of the sandwich method: etching solution is ...Figure 5.6 Schematic representation of the VPD method. After an exposition in HF...Figure 5.7 Schematic representation of the immersion method: a wafer is extracte...Figure 5.8 Schematic representation of the sequential etching method to locate i...Figure 5.9 Elemental contaminations in different layers of a metallurgical silic...Figure 5.10 Summed up masses of impurities of sequential etching steps and final...Figure 5.11 Measured contact angle of a liquid on silicon wafer surface at the t...Figure 5.12 Wafer map of the contact angles measured with water and diiodomethan...Figure 5.13 Results for TOC measurements and from contact angle calculated surfa...