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Table of contents
Acknowledgements
General introduction
Part 1. State-of-the-art
I. Towards higher passivation level for c-Si solar cells
1. Working principle of conventional c-Si solar cells
2. Main loss mechanisms of a c-Si solar cell
3. Concept of full-area passivating contacts
II. Poly-Si contact fabrication and integration in solar cells
1. Brief historical review
2. Working principle of the poly-Si contact
3. Fabrication process of the poly-Si contact
a. Growth of the thin SiOx layer
b. Si-based layer deposition and doping
c. Annealing step
d. Hydrogenation step
4. Integration of the poly-Si contact in c-Si solar cells
a. Record efficiencies on small area solar cells
b. Towards industrial solar cells integrating the poly-Si contact
i. The metallization challenge
ii. Large area c-Si solar cells integrating the poly-Si contact
III. Current understanding of the passivation and transport mechanisms
1. Control of the final surface passivation
a. Growth of the SiOx layer
b. Role of doping
c. Optimization of the annealing temperature
d. Role of hydrogen
2. Transport of charge carriers through the SiOx layer
Part 2. Experimental
I. Fabrication process of B-doped poly-Si/SiOx contacts by PECVD
1. Si-based layers by Plasma-Enhanced Chemical Vapor Deposition (PECVD)
2. c-Si substrates and samples configuration
3. Fabrication of in-situ doped poly-Si/SiOx contacts
4. SiOxNy:B layers for ex-situ doping of the poly-Si/SiOx contacts
II. Characterization techniques
1. Structural and chemical characterization
a. Thickness and microstructure of the layers
i. Spectroscopic ellipsometry
ii. Transmission Electron Microscopy
b. SiOx chemical composition: X-ray Photoelectron Spectroscopy
c. Doping profiles in a-Si:H and poly-Si layers
i. Electrochemical Capacitance-Voltage
ii. Secondary Ions Mass Spectroscopy
2. Electronic characterizations
a. Electrical properties of the poly-Si layer: Hall effect technique
b. Lifetime measurements: Photo Conductance Decay
c. Defect characterization in c-Si: lifetime spectroscopy
i. SRH description of an electrically active defect center
ii. Lifetime spectroscopy methods
iii. Case of several SRH defect centers
iv. Bulk and surface contributions to the effective lifetime
v. SRH formalism at the surface
d. Transport of charge carriers in the poly-Si/SiOx contact: Conductive Atomic Force Microscopy
Part 3: Fabrication of the poly-Si/SiOx contact
I. Optimization of the in-situ doped poly-Si/SiOx contact
1. Optimization of the deposition conditions for blister-free poly-Si(B) layers
a. Effect of the deposition temperature increase
b. Effect of the silane dilution in dihydrogen
c. Evaluation of the poly-Si electrical properties through deposition optimizations
d. Effect of the blistering on the stability of surface passivation
2. Crystallization and doping of the poly-Si layer
a. Crystallization of the poly-Si layer
b. Doping of the poly-Si layer
3. Surface passivation properties of the in-situ doped poly-Si(B)/SiOx contact
a. Impact of the annealing temperature
b. Impact of the hydrogenation step
II. Ex-situ doping of the poly-Si/SiOx contact
1. Deposition of the intrinsic Si layer by PECVD
a. Decrease of the in-situ B-doping
b. Optimization of the intrinsic Si layer
2. Ex-situ doping
a. Si layer microstructure
b. Comparison of the two ex-situ doping processes
i. Electrical properties
ii. Passivation properties
c. Doping profile of the ex-situ doped poly-Si/SiOx contact
3. Comparison of in-situ and ex-situ doped poly-Si/SiOx contacts
a. Si-layer microstructure
i. After deposition
ii. After annealing
b. Electrical properties
c. Surface passivation properties
4. Effect of the doping density and hydrogen diffusion on surface passivation
a. Passivation stability upon annealing and SiN:H deposition
b. H diffusion profile in poly-Si(i) and poly-Si(B) contacts
c. Effect of the firing temperature
Conclusion
Part 4. Investigation of the poly-Si/SiOx interface
I. Chemical and structural evolution of the SiOx layer
1. SiOx grown at the c-Si surface
a. Ex-situ annealing in the tube furnace
b. In-situ annealing in the XPS chamber
c. Quantitative comparison of the XPS spectra after annealing
2. XPS study of the poly-Si/SiOx/c-Si stack
a. Qualitative study of the oxides upon annealing
b. Quantitative analysis
c. Structural evolution of the SiOx at the poly-Si/c-Si interface
3. Conclusions on XPS and TEM analysis of the interface
II. Investigation of the transport mechanism within the SiOx layer
1. Impact of the surface preparation of the sample on the C-AFM measurement
2. C-AFM investigation of the pinholes formation within the SiOx layer
a. Transversal measurements
i. With and without interfacial SiOx
ii. Comparison of chemical and thermal interfacial SiOx layers
b. Lateral C-AFM measurements
3. KPFM investigation of the pinholes formation within the SiOx layer
III. Study of the poly-Si/c-Si interface recombination by lifetime spectroscopy
1. Sample preparation
2. Extraction of the surface recombination velocity
3. Linearization of τsurf using Murphy’s approach
4. Lifetime spectroscopy for the determination of the defect parameters
Conclusion
General conclusion and perspectives
Appendix A: Correction of ECV profiles measured on ex-situ doped poly-Si contacts
Appendix B: Fitting procedure of the XPS Si 2p spectral range of a SiOx layer
List of publications
Résumé des travaux
References
