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- Marquez, Jose A., et al.
(författare)
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High-temperature decomposition of Cu2BaSnS4 with Sn loss reveals newly identified compound Cu2Ba3Sn2S8
- 2020
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Ingår i: Journal of Materials Chemistry A. - : Royal Society of Chemistry (RSC). - 2050-7488 .- 2050-7496. ; 8:22, s. 11346-11353
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Tidskriftsartikel (refereegranskat)abstract
- The earth-abundant quaternary compound Cu(2)BaSnS(4)is being currently studied as a candidate for photovoltaics and as a photocathode for water splitting. However, the chemical stability of this phase during synthesis is unclear. The synthesis of other quaternary tin-sulphur-based absorbers (e.g., Cu2ZnSnS4) involves an annealing step at high temperature under sulphur gas atmosphere, which can lead to decomposition into secondary phases involving Sn loss from the sample. As the presence of secondary phases can be detrimental for device performance, it is crucial to identify secondary phase chemical, structural and optoelectronic properties. Here we used a combination ofin situEDXRD/XRF and TEM to identify a decomposition pathway for Cu2BaSnS4. Our study reveals that, while Cu(2)BaSnS(4)remains stable at high sulphur partial pressure, the material decomposes at high temperatures into Cu(4)BaS(3)and the hitherto unknown compound Cu(2)Ba(3)Sn(2)S(8)if the synthesis is performed under low partial pressure of sulphur. The presence of Cu(4)BaS(3)in devices could be harmful due to its high conductivity and relatively lower band gap compared to Cu2BaSnS4. The analysis of powder diffraction data reveals that the newly identified compound Cu(2)Ba(3)Sn(2)S(8)crystallizes in the cubic system (space groupI4x304;3d) with a lattice parameter ofa= 14.53(1) angstrom. A yellow powder of Cu(2)Ba(3)Sn(2)S(8)has been synthesized, exhibiting an absorption onset at 2.19 eV.
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| 3. |
- Suchan, Klara, et al.
(författare)
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Multi-Stage Phase-Segregation of Mixed Halide Perovskites under Illumination : A Quantitative Comparison of Experimental Observations and Thermodynamic Models
- 2023
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Ingår i: Advanced Functional Materials. - : Wiley. - 1616-301X .- 1616-3028. ; 33:3
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Tidskriftsartikel (refereegranskat)abstract
- Photo- and charge-carrier-induced ion migration is a major challenge when utilizing metal halide perovskite semiconductors for optoelectronic applications. For mixed iodide/bromide perovskites, the compositional instability due to light- or electrical bias induced phase-segregation restricts the exploitation of the entire bandgap range. Previous experimental and theoretical work suggests that excited states or charge carriers trigger the process, but the exact mechanism is still under debate. To identify the mechanism and cause of light-induced phase-segregation phenomena, the full compositional range of methylammonium lead bromide/iodide samples are investigated, MAPb(BrxI1-x)3 with x = 0…1, by simultaneous in situ X-ray diffraction (XRD) and photoluminescence (PL) spectroscopy during illumination. The quantitative comparison of composition-dependent in situ XRD and PL shows that at excitation densities of 1 sun, only the initial stage of photo-segregation is rationalized with the previously established thermodynamic models. However, a progression of the phase segregation is observed that is rationalized by considering long-lived accumulative photo-induced material alterations. It is suggested that (additional) photo-induced defects, possibly halide vacancies and interstitials, need to be considered to fully rationalize light-induced phase segregation and anticipate the findings to provide crucial insight for the development of more sophisticated models.
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| 4. |
- Thomas, Sinju, et al.
(författare)
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Effects of material properties of band-gap-graded Cu(In,Ga)Se-2 thin films on the onset of the quantum efficiency spectra of corresponding solar cells
- 2022
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Ingår i: Progress in Photovoltaics. - : John Wiley & Sons. - 1062-7995 .- 1099-159X. ; 30:10, s. 1238-1246
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Tidskriftsartikel (refereegranskat)abstract
- Polycrystalline Cu(In,Ga)Se-2 (CIGSe) thin-film solar cells exhibit gradual onset in their external quantum efficiency (EQE) spectra whose shape can be affected by various CIGSe material properties. Apart from influences on the charge-carrier collection, a broadening of the EQE onset leads to enhanced radiative losses in open-circuit voltage (V-oc). In the present work, Gaussian broadening of parameters describing the EQE onset of thin-film solar cells, represented by the standard deviation, sigma(total), was evaluated to study the impacts of the effective band-gap energy, the electron diffusion length, and the Ga/In gradient in the CIGSe absorber. It is shown that sigma(total) can be disentangled into contributions of these material properties, in addition to a residual component sigma(residual). Effectively, sigma(total) depends only on a contribution related to the Ga/In gradient as well as on sigma(residual). The present work highlights the connection of this compositional gradient, the microstructure in the polycrystalline CIGSe absorber, and the luminescence emission with the residual component sigma(residual). It is demonstrated that a flat band-gap with no compositional gradient in the bulk of the CIGSe absorber is essential to obtain the lowest sigma(total) values and thus result in lower recombination losses and gains in V-oc.
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