| 1. |
- Erbing, Axel, 1991-
(author)
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In pursuit of next generation photovoltaics : An electronic structure study of emerging solar cell materials
- 2022
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Doctoral thesis (other academic/artistic)abstract
- The development of a new generation of photovoltaic technologies is an important task in order to increase the production of clean energy. Perovskite solar cells, with an exceptionally rapid development over the last decade, have transformed into perhaps the most promising candidate to provide a low-cost alternative to conventional cells. While having excellent efficiency, the most successful category of photovoltaic perovskites, the class of hybrid lead-halide perovskites, suffers from poor stability in ambient conditions and gives rise to potential health concerns due to lead toxicity. Because of these issues, studies yielding a better understanding of lead-based perovskites and investigations of new, lead-free materials are likely meaningful steps towards better and more competitive solar cells. This thesis contains studies about established lead-based perovskites, CH3NH3PbI3 and CH(NH2)2PbI3, as well as the lead-free alternatives AgBi2I7 and Cs2AgBiI6. The main method employed is electronic structure calculations through density functional theory under periodic boundary conditions including band structure calculations and projected density of states. A particular focus is given to systems with mixed anion and related effects on the electronic structure.
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| 2. |
- Erbing, Axel, 1991-, et al.
(author)
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Spatial microheterogeneity in the valence band of mixed halide hybrid perovskite materials
- 2022
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In: Chemical Science. - : Royal Society of Chemistry (RSC). - 2041-6520 .- 2041-6539. ; 13:32, s. 9285-9294
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Journal article (peer-reviewed)abstract
- The valence band of lead halide hybrid perovskites with a mixed I/Br composition is investigated using electronic structure calculations and complementarily probed with hard X-ray photoelectron spectroscopy. In the latter, we used high photon energies giving element sensitivity to the heavy lead and halide ions and we observe distinct trends in the valence band as a function of the I : Br ratio. Through electronic structure calculations, we show that the spectral trends with overall composition can be understood in terms of variations in the local environment of neighboring halide ions. From the computational model supported by the experimental evidence, a picture of the microheterogeneity in the valence band maximum emerges. The microheterogeneity in the valence band suggests that additional charge transport mechanisms might be active in lead mixed halide hybrid perovskites, which could be described in terms of percolation pathways.
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| 3. |
- Garcia Fernandez, Alberto, et al.
(author)
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Experimental and Theoretical Core Level and Valence Band Analysis of Clean Perovskite Single Crystal Surfaces
- 2022
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In: Small. - : Wiley. - 1613-6810 .- 1613-6829. ; 18:13
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Journal article (peer-reviewed)abstract
- A detailed understanding of the surface and interface properties of lead halide perovskites is of interest for several applications, in which these materials may be used. To develop this understanding, the study of clean crystalline surfaces can be an important stepping stone. In this work, the surface properties and electronic structure of two different perovskite single crystal compositions (MAPbI(3) and Cs(x)FA(1-)(x)PbI(3)) are investigated using synchrotron-based soft X-ray photoelectron spectroscopy (PES), molecular dynamics simulations, and density functional theory. The use of synchrotron-based soft X-ray PES enables high surface sensitivity and nondestructive depth-profiling. Core level and valence band spectra of the single crystals are presented. The authors find two carbon 1s contributions at the surface of MAPbI(3) and assign these to MA(+) ions in an MAI-terminated surface and to MA(+) ions below the surface. It is estimated that the surface is predominantly MAI-terminated but up to 30% of the surface can be PbI2-terminated. The results presented here can serve as reference spectra for photoelectron spectroscopy investigations of technologically relevant polycrystalline thin films, and the findings can be utilized to further optimize the design of device interfaces.
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