Browsing by Author "Mitzi, DB"
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Item Open Access Carrier Dynamics Engineering for High-Performance Electron-Transport-Layer-free Perovskite Photovoltaics(CHEM, 2018-10-11) Han, Q; Ding, J; Bai, Y; Li, T; Ma, JY; Chen, YX; Zhou, Y; Liu, J; Ge, QQ; Chen, J; Glass, JT; Therien, MJ; Liu, J; Mitzi, DB; Hu, JSItem Open Access Structural Tolerance Factor Approach to Defect-Resistant I2-II-IV-X4 Semiconductor Design(Chemistry of Materials, 2020-02-25) Sun, JP; McKeown Wessler, GC; Wang, T; Zhu, T; Blum, V; Mitzi, DBCopyright © 2020 American Chemical Society. Recent work on quaternary semiconductors Cu2BaSn(S,Se)4 and Ag2BaSnSe4 for photovoltaic and thermoelectric applications, respectively, has shown the promise of exploring the broader family of defect-resistant I2-II-IV-X4 materials (where I, II, and IV refer to the formal oxidation state of the metal cations and X is a chalcogen anion) with tetrahedrally coordinated I/IV cations and larger II cations (i.e., Sr, Ba, Pb, and Eu) for optoelectronic and energy-related applications. Chemical dissimilarity among the II and I/IV atoms represents an important design motivation because it presents a barrier to antisite formation, which otherwise may act as electronically harmful defects. We herein show how all 31 experimentally reported I2-II-IV-X4 examples (with large II cations and tetrahedrally coordinated smaller I/IV cations), which form within five crystal structure types, are structurally linked. Based on these structural similarities, we derive a set of tolerance factors that serve as descriptors for phase stability within this family. Despite common usage in the well-studied perovskite system, Shannon ionic radii are found to be insufficient for predicting metal-chalcogen bond lengths, pointing to the need for experimentally derived correction factors as part of an empirically driven learning approach to structure prediction. We use the tolerance factors as a predictive tool and demonstrate that four new I2-II-IV-X4 compounds, Ag2BaSiS4, Ag2PbSiS4, Cu2PbGeS4, and Cu2SrSiS4, can be synthesized in correctly predicted phases. One of these compounds, Ag2PbSiS4, shows potentially promising optoelectronic properties for photovoltaic applications.Item Open Access Suns- VOC characteristics of high performance kesterite solar cells(Journal of Applied Physics, 2014-01-01) Gunawan, O; Gokmen, T; Mitzi, DBLow open circuit voltage (VOC) has been recognized as the number one problem in the current generation of Cu2ZnSn(Se,S)4 (CZTSSe) solar cells. We report high light intensity and low temperature Suns-VOC measurement in high performance CZTSSe devices. The Suns-VOC curves exhibit bending at high light intensity, which points to several prospective VOC limiting mechanisms that could impact the VOC, even at 1 sun for lower performing samples. These V OC limiting mechanisms include low bulk conductivity (because of low hole density or low mobility), bulk or interface defects, including tail states, and a non-ohmic back contact for low carrier density CZTSSe. The non-ohmic back contact problem can be detected by Suns-VOC measurements with different monochromatic illuminations. These limiting factors may also contribute to an artificially lower JSC-VOC diode ideality factor. © 2014 AIP Publishing LLC.