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Optoelectronic and Defect Properties in Earth Abundant Photovoltaic Materials: First-principle Calculations

Shi, Tingting
http://rave.ohiolink.edu/etdc/view?acc_num=toledo1418391935

Abstract Details

2014, Doctor of Philosophy, University of Toledo, College of Natural Sciences and Mathematics.
In this dissertation, a series of earth-abundant photovoltaic materials including lead halide perovskites, copper based compounds, and silicon are investigated via density functional theory (DFT). Firstly, we study the unique optoelectronic properties of perovskite CH3NH3PbI3 and CH3NH3PbBr3. First-principle calculations show that CH3NH3PbI3 perovskite solar cells exhibit remarkable optoelectronic properties that account for the high open circuit voltage (Voc) and long electron-hole diffusion lengths. Our results reveal that for intrinsic doping, dominant point defects produce only shallow levels. Therefore lead halide perovskites are expected to exhibit intrinsic low non-radiative recombination rates. The conductivity of perovskites can be tuned from p-type to n-type by controlling the growth conditions. For extrinsic defects, the p-type perovskites can be achieved by doping group-IA, -IB, or -VIA elements, such as Na, K, Rb, Cu, and O at I-rich growth conditions. We further show that despite a large band gap of 2.2 eV, the dominant defects in CH3NH3PbBr3 also create only shallow levels. The photovoltaic properties of CH3NH3PbBr3–based perovskite absorbers can be tuned via defect engineering. Highly conductive p-type CH3NH3PbBr3 can be synthesized under Br-rich growth conditions. Such CH3NH3PbBr3 may be potential low-cost hole transporting materials for lead halide perovskite solar cells. All these unique defect properties of perovskites are largely due to the strong Pb lone-pair s orbital and I p (Br p) orbital antibonding coupling and the high ionicity of CH3NH3PbX3 (X=I, Br). Secondly, we study the optoelectronic properties of Cu-V-VI earth abundant compounds. These low cost thin films may have the good electronic and optical properties. We have studied the structural, electronic and optical properties of Cu3-V-VI4 compounds. After testing four different crystal structures, enargite, wurtzite-PMCA, famatinite and zinc-blend-PMCA, we find that Cu3PS4 and Cu3PSe4 prefer energetically the enargite structure, whereas, other compounds favor the famatinite structure. Among the compounds and structures considered, enargite Cu3PSe4, and famatinite Cu3AsS4, are suitable for single junction solar cell applications due to bandgaps of 1.32 eV and 1.15 eV, respectively. Furthermore, CuSbS2 are also studied by density functional theory and HSE06 hybrid functional. The chalcostibite CuSbS2 has an indirect band gap of 1.85 eV, whereas the chalcogenide Cu3SbS4 has a direct band gap of 0.89 eV. We find that the large difference on band gaps is mainly attributed to the different Sb charge states. We further predict that the Sb charge states will affect the defect physics. Particularly, the Sb lone pair s orbitals in CuSbS2 have strong influence on the formation energies of Sb-related defects. Lastly, we have studied the atomic structure and electronic properties of aluminum (Al)-related defect complexes in silicon. We find a unique stable complex configuration consisting of an Ali and an oxygen dimer, Ali-2Oi, which introduces deep levels in the band gap of Si. The formation energies of the Ali-2Oi complexes could be lower than that of individual Ali atoms under oxygen-rich conditions. The formation of Ali-2Oi complexes may explain the experimental observation that the coexistence of Al and O results in reduced carrier lifetime in Si wafers.
Yanfa Yan (Advisor)
Robert Collins (Committee Member)
Jacques Amar (Committee Member)
Bo Gao (Committee Member)
Rashmi Jha (Committee Member)
122 p.
Physics
Perovskites solar cell, Density functional theory

Recommended Citations

Citations

  • Shi, T. (2014). Optoelectronic and Defect Properties in Earth Abundant Photovoltaic Materials: First-principle Calculations [Doctoral dissertation, University of Toledo]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=toledo1418391935

    APA Style (7th edition)

  • Shi, Tingting. Optoelectronic and Defect Properties in Earth Abundant Photovoltaic Materials: First-principle Calculations . 2014. University of Toledo, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=toledo1418391935.

    MLA Style (8th edition)

  • Shi, Tingting. "Optoelectronic and Defect Properties in Earth Abundant Photovoltaic Materials: First-principle Calculations ." Doctoral dissertation, University of Toledo, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=toledo1418391935

    Chicago Manual of Style (17th edition)

toledo1418391935
1,369
© 2014, some rights reserved.Creative Commons License Optoelectronic and Defect Properties in Earth Abundant Photovoltaic Materials: First-principle Calculations by Tingting Shi is licensed under a Creative Commons Attribution-NonCommercial-NoDerivs 3.0 Unported License. Based on a work at etd.ohiolink.edu.
This open access ETD is published by University of Toledo and OhioLINK.