Full metadata
Title
Modeling towards lattice-matched dilute nitride GaNPAs on silicon multijunction solar cells
Description
Silicon photovoltaics is the dominant contribution to the global solar energy production. As increasing conversion efficiency has become one of the most important factors to lower the cost of photovoltaic systems, the idea of making a multijunction solar cell based on a silicon bottom cell has attracted broad interest. Here the potential of using dilute nitride GaNPAs alloys for a lattice-matched 3-terminal 2-junction Si-based tandem solar cell through multiscale modeling is investigated. To calculate the electronic band structure of dilute nitride alloys with relatively low computational cost, the sp^3 d^5 s^* s_N tight-binding model is chosen, as it has been demonstrated to obtain quantitatively correct trends for the lowest conduction band near Γ, L, and X for dilute-N GaNAs. A genetic algorithm is used to optimize the sp^3 d^5 s^* tight-binding model for pure GaP and GaAs for their optical properties. Then the optimized sp^3 d^5 s^* s_N parametrizations are obtained for GaNP and GaNAs by fitting to experimental bandgap values. After that, a virtual crystal approach gives the Hamiltonian for GaNPAs alloys. From their tight-binding Hamiltonian, the first-order optical response functions of dilute nitride GaNAs, GaNP, and GaNPAs are calculated. As the N mole fraction varies, the calculated critical optical features vary with the correct trends, and agree well with experiment. The calculated optical properties are then used as input for the solar device simulations based on Silvaco ATLAS. For device simulation, a bottom cell model is first constructed to generate performance results that agree well with a demonstrated high-efficiency Si heterojunction interdigitated back contact (IBC) solar cell reported by Kaneka. The front a-Si/c-Si interface is then replaced by a GaP/Si interface for the investigation of the sensitivity of the GaP/Si interface to interface defects in terms of degradation of the IBC cell performance, where we find that an electric field that induces strong band bending can significantly mitigate the impact of the interfacial traps. Finally, a lattice-matched 3-terminal 2-junction tandem model is built for performance simulation by stacking a dilute nitride GaNP(As) cell on the Si IBC cell connected through a GaP/Si interface. The two subcells operate quasi-independently. In this 3-terminal tandem model, traps at the GaP/Si interface still significantly impact the performance of the Si subcell, but their effects on the GaNP subcell are relatively small. Assuming the interfacial traps are well passivated, the tandem efficiency surpasses that of a single-junction Si cell, with values close to 33% based on realistic parameters.
Date Created
2019
Contributors
- Zou, Yongjie (Author)
- Goodnick, Stephen M. (Thesis advisor)
- Honsberg, C. (Christiana B.) (Committee member)
- King, Richard R. (Committee member)
- Vasileska, Dragica (Committee member)
- Arizona State University (Publisher)
Topical Subject
Resource Type
Extent
xii, 101 pages : color illustrations
Language
eng
Copyright Statement
In Copyright
Primary Member of
Peer-reviewed
No
Open Access
No
Handle
https://hdl.handle.net/2286/R.I.54918
Statement of Responsibility
by Yongjie Zou
Description Source
Viewed on August 26, 2020
Level of coding
full
Note
thesis
Partial requirement for: Ph.D., Arizona State University, 2019
bibliography
Includes bibliographical references
Field of study: Electrical engineering
System Created
- 2019-11-06 03:39:44
System Modified
- 2021-08-26 09:47:01
- 3 years 2 months ago
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