Dissertation
OPTIMIZATION OF N-TYPE CDTE AND CD-SE-TE FOR NEXT-GENERATION SOLAR CELLS
Doctor of Philosophy (PhD), Washington State University
12/2025
DOI:
https://doi.org/10.7273/000008392
Abstract
This dissertation establishes a comprehensive framework for advancing cadmium telluride (CdTe) photovoltaics through a systematic exploration of n-type absorber design, defect control, surface passivation, thin-film epitaxy, and device simulation. While conventional p-type CdTe has reached a practical efficiency plateau, this work demonstrates that iodine-doped n-type CdTe (CdTe:I) and indium-doped Cd-Se-Te (CST:In) can overcome intrinsic limitations. Using thermoelectric effect spectroscopy (TEES), Hall-effect, photoluminescence (PL), and density functional theory (DFT), the fundamental defect levels of CdTe:I were identified, revealing shallow donors (ITe ~0.05 eV) and compensating acceptors (VCd, ITe–VCd) that govern Fermi-level pinning. Post-growth Cd annealing was shown to suppress compensation centers, activate iodine donors, and reduce resistivity, enabling high-quality n-type material. At the interface level, Br passivation most effectively reduced surface recombination, while CdCl₂ improved bulk lifetime, highlighting their distinct chemical roles. Thin films fabricated by close-spaced sublimation epitaxy (CSSE) confirmed epitaxial growth of CdTe:In, CdTe:I, and CST:In, and preliminary homojunction devices established the feasibility of all-CdTe n-type structures. Further, SCAPS-1D simulations predicted efficiencies >25% for optimized MXene/p-CdTe:As/n-CdTe:I/In designs, while prototype devices revealed performance losses from mobility degradation and interface recombination. Extending to ternary alloys, CST:In crystals exhibited nearly 100% dopant activation, electron concentration up to 9.5×10¹⁸ cm⁻³, mobility >600 cm²/V·s, and lifetimes approaching the radiative limit—demonstrating a new high-performance absorber platform without intensive post-growth treatment. Overall, this dissertation pioneers the transition from p-type to n-type CdTe absorber technologies, integrates bulk single-crystal and thin-film approaches, and provides both mechanistic insights and design principles for next-generation CdTe-based solar cells.
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Details
- Title
- OPTIMIZATION OF N-TYPE CDTE AND CD-SE-TE FOR NEXT-GENERATION SOLAR CELLS
- Creators
- Jing Shang
- Contributors
- John S McCloy (Chair)Scott P Beckman (Committee Member)Matthew D McCluskey (Committee Member)
- Awarding Institution
- Washington State University
- Academic Unit
- School of Mechanical and Materials Engineering
- Theses and Dissertations
- Doctor of Philosophy (PhD), Washington State University
- Number of pages
- 228
- Identifiers
- 99901357897601842
- Language
- English
- Resource Type
- Dissertation