Density functional theory and Green's function approach to investigate cadmium telluride based thin film photovoltaics

Nicholson, Anthony P., author
Sampath, Walajabad S., advisor
Weinberger, Chris, advisor
Popat, Ketul, committee member
Sites, James, committee member
Martinez, Umberto, committee member
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In recent years, cadmium telluride (CdTe) based thin film photovoltaics (PV) have exhibited remarkable improvements in overall efficiency and device performance. As the most notable thin film PV technology, CdTe PV is developed and manufactured in the U.S. as the leading cost-competitive option for electricity generation in comparison to other PV technologies such as silicon and CIGS PV. However, CdTe PV faces major challenges that limit its achievable performance during the solar energy conversion process. It has become increasingly evident that to improve PV efficiency, an understanding of surfaces and interfaces is necessary. Therefore, high-fidelity quantum-based atomistic simulations will be used to calculate energy band alignment of CdTe thin film surfaces and interfaces to resolve the issues found in such problematic areas and advance PV efficiency. Ab initio simulation models implement density functional theory (DFT) coupled with Green's function (GF) for investigating the electronic and structural properties of thin film surfaces and interfaces within CdTe PV device configurations. Comprehensive studies on spatially-dependent energy band alignments with respect to plane orientation, terminated surfaces, carrier concentrations and elemental composition were computationally evaluated to determine their possible effect on CdTe solar cell device performance. A total of 14 unique CdTe-based surfaces and 3 different CdTe/Te interfaces were simulated to determine their effect on energy band alignment. A number of key insights were gained that include: 1) the band bending directions dictated by the termination layer based on surface theory; 2) the role of surface reconstruction in flattening the CdTe surface energy band alignments while neutralizing surface states due to the fulfillment of the electron counting rule; 3) the formation of a cusp energy potential feature along the CdTe{111} plane oriented energy band alignments as observed by external literature studies within the CdTe/Te interface. Results to date indicate that the DFT+GF atomistic modeling approach to constructing energy band alignments matches closer to experiments than conventional band alignment methods. State-of-the-art DFT+GF calculations on CdTe-based thin film surfaces and interfaces provide a methodology for studying quantum mechanical effects in thin film PV devices such as high-efficiency single junction CdTe solar cells and tandem solar cells.
Includes bibliographical references.
2020 Summer.
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cadmium telluride
energy band alignment
atomistic modeling
Green's function
density functional theory
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