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| 2. |
- Johansson, Malin B, 1972-, et al.
(author)
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Cesium Bismuth Iodide Solar Cells from Systematic Molar Ratio Variation of CsI and BiI3
- 2019
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In: Inorganic Chemistry. - : AMER CHEMICAL SOC. - 0020-1669 .- 1520-510X. ; 58:18, s. 12040-12052
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Journal article (peer-reviewed)abstract
- Metal halide compounds with photovoltaic properties prepared from solution have received increased attention for utilization in solar cells. In this work, low-toxicity cesium bismuth iodides are synthesized from solution, and their photovoltaic and, optical properties as well as electronic and crystal structures are investigated. The X-ray diffraction patterns reveal that a CsI/BiI3 precursor ratio of 1.5:1 can convert pure rhombohedral BiI3 to pure hexagonal Cs3Bi2I9, but any ratio intermediate of this stoichiometry and pure BiI3 yields a mixture containing the two crystalline phases Cs3Bi2I9 and BiI3, with their relative fraction depending on the CsI/BiI3 ratio. Solar cells from the series of compounds are characterized, showing the highest efficiency for the compounds with a mixture of the two structures. The energies of the valence band edge were estimated using hard and soft X-ray photoelectron spectroscopy for more bulk and surface electronic properties, respectively. On the basis of these measurements, together with UV-vis-near-IR spectrophotometry, measuring the band gap, and Kelvin probe measurements for estimating the work function, an approximate energy diagram has been compiled clarifying the relationship between the positions of the valence and conduction band edges and the Fermi level.
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| 4. |
- Johansson, Malin B., et al.
(author)
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Extended Photo-Conversion Spectrum in Low-Toxic Bismuth Halide Perovskite Solar Cells
- 2016
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In: The Journal of Physical Chemistry Letters. - : American Chemical Society (ACS). - 1948-7185. ; 7:17, s. 3467-3471
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Journal article (peer-reviewed)abstract
- Lead-based perovskites show very promising properties for use in solar cells; however, the toxicity of lead is a potential inhibitor for large-scale application of these solar cells. Here, a low-toxic bismuth halide, CsBi3I10, is synthesized from solution and the optical properties and crystal structure are compared with previously reported Cs3Bi2I9 perovskite, and the photovoltaic properties are also investigated. The XRD pattern suggests that the CsBi3I10 film has a layered structure with a different dominating crystal growth direction than the Cs3Bi2I9 perovskite. A band gap of 1.77 eV is obtained for the CsBi3I10 film, which is smaller than the band gap of Cs3Bi2I9 at 2.03 eV, and an extended visible light absorption spectrum is therefore obtained. The solar cell device with CsBi3I10 shows a photocurrent up to 700 nm, and this work shows therefore the possibility for increased light absorption and higher photocurrents in solar cells based on bismuth halide perovskites.
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| 5. |
- Liu, Yawen, et al.
(author)
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Flexible Lead Bromide Perovskite Solar Cells
- 2020
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In: ACS Applied Energy Materials. - : AMER CHEMICAL SOC. - 2574-0962. ; 3:10, s. 9817-9823
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Journal article (peer-reviewed)abstract
- Lead bromide perovskite solar cells (PSCs) have attracted increasing interest partly because of the high open-circuit voltage that has been obtained. Here, we present a simple way to prepare PSCs based on formamidinium lead tribromide, FAPbBr(3), by adding methylammonium chloride and methylammonium bromide into the precursor solution. With this method, high-quality and pin-hole free perovskite films with large crystal sizes were prepared. These additives result in a power conversion efficiency (PCE) of 7.9%, almost free of hysteresis, for a device on a rigid glass substrate. The first flexible lead bromide PSC is also prepared in this work and the flexible PSC exhibited a high PCE of 5.0%.
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| 6. |
- Pazoki, Meysam, et al.
(author)
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Bismuth Iodide Perovskite Materials for Solar Cell Applications : Electronic Structure, Optical Transitions and Directional Charge Transport
- 2016
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In: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 120, s. 29039-29046
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Journal article (peer-reviewed)abstract
- Cesium and methylammonium bismuth iodides (Cs3Bi2I9 and MA(3)Bi(2)I(9)) are new low-toxic and air stable compounds in the perovskite solar cell family with promising characteristics. Here, the electronic structure and the nature of their optical transitions, dielectric constant, and charge carrier properties are assessed for photovoltaic applications with density functional theory (DFT) calculations and experiments. The calculated direct and indirect band gap values for Cs3Bi2I9 (2.17 and 2.0 eV) and MA(3)Bi(2)I(9) (2.17 and 1.97 eV) are found to be in good agreement with the experimental optical band gaps (2.2, 2.0 eV and 2.4, 2.1 eV for Cs3Bi2I9 and MA(3)Bi(2)I(9), respectively) estimated for solution-processed films. There is an error cancelation in the DFT calculated band gap similar to that for lead perovskites. However, fully relativistic DFT calculations indicate that the size of the spin orbit coupling (SOC) error cancelation for bismuth perovskite (0.5 eV) is less than for lead perovskite (1 eV), and other factors are therefore also important. Band structure calculations show high effective masses of the charge carriers along the c-axis but on the other hand lower electron effective mass in the a-b planes, revealing the interesting possibility for a directional charge transport. Calculations of dielectric constants, absorption coefficients, carrier effective masses, and exciton binding energies emphasize the fundamental differences between the lead and bismuth iodide perovskites and clarify the reasons behind the lower power conversion efficiency of bismuth iodide perovskite solar cells. Also the calculations show that the orientational disorder of the MA dipoles in the lattice has meaningful impacts on the near valence and conduction band edge of the electronic structure.
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| 7. |
- Peng, Jianhui, et al.
(author)
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Achieving ultra-high electromagnetic wave absorption by anchoring Co0.33Ni0.33Mn0.33Fe2O4 nanoparticles on graphene sheets using microwave-assisted polyol method
- 2018
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In: Ceramics International. - : ELSEVIER SCI LTD. - 0272-8842 .- 1873-3956. ; 44:17, s. 21015-21026
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Journal article (peer-reviewed)abstract
- The Co0.33Ni0.33Mn0.33Fe2O4/graphene nanocomposite for electromagnetic wave absorption was successfully synthesized from metal chlorides solutions and graphite powder by a simple and rapid microwave-assisted polyol method via anchoring the Co0.33Ni0.33Mn0.33Fe2O4 nanoparticles on the layered graphene sheets. The Fe3+, Co2+, Ni2+ and Mn2+ ions in the solutions were attracted by graphene oxide obtained from graphite and converted to the precursors Fe(OH)(3), Co(OH)(2), Ni(OH)(2), and Mn(OH)(2) under slightly alkaline conditions. After the transformations of the precursors to Co-Ni-Mn ferrites and conversion of graphene oxide to graphene under microwave irradiation at 170 degrees C in just 25 min, the Co0.33Ni0.33Mn0.33Fe2O4/graphene nanocomposite was prepared. The composition and structure of the nanocomposite were characterized by X-ray diffraction (XRD), inductive coupled plasma emission spectroscopy (ICP), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FT-IR), Raman spectroscopy (RS), transmission electron microscopy (TEM), etc. It was found that with the filling ratio of only 20 wt% and the thickness of 2.3 mm, the nanocomposite showed an ultra-wide effective absorption bandwidth (less than -10 dB) of 8.48 GHz (from 9.52 to 18.00 GHz) with the minimum reflection loss of - 24.29 dB. Compared to pure graphene sheets, Co0.33Ni0.33Mn0.33Fe2O4 nano particles and the counterparts reported in literature, the nanocomposite exhibited much better electromagnetic wave absorption, mainly attributed to strong wave attenuation, as a result of synergistic effects of dielectric loss, conductive loss and magnetic loss, and to good impedance matching. In view of its thin thickness, light weight and outstanding electromagnetic wave absorption property, the nanocomposite could be used as a very promising electromagnetic wave absorber.
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| 8. |
- Wu, Hua, et al.
(author)
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Bandgap Tuning of Silver Bismuth Iodide via Controllable Bromide Substitution for Improved Photovoltaic Performance
- 2019
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In: ACS Applied Energy Materials. - : American Chemical Society (ACS). - 2574-0962. ; 2:8, s. 5356-5362
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Journal article (peer-reviewed)abstract
- In this work, silver-bismuth-halide thin films, exhibiting low toxicity and good stability, were explored systemically by gradually substituting iodide, I, with bromide, Br, in the AgBi2I7 system. It was found that the optical bandgap can be tuned by varying the I/Br ratio. Moreover, the film quality was improved when introducing a small amount of Br. The solar cell was demonstrated to be more stable at ambient conditions and most efficient when incorporating 10% Br, as a result of decreased recombination originating from the increased grain size. Thus, replacing a small amount of I with Br was beneficial for photovoltaic performance.
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| 9. |
- Zhu, Huimin, et al.
(author)
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High Photon-to-Current Conversion in Solar Cells Based on Light-Absorbing Silver Bismuth Iodide
- 2017
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In: ChemSusChem. - : WILEY-V C H VERLAG GMBH. - 1864-5631 .- 1864-564X. ; 10:12, s. 2592-2596
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Journal article (peer-reviewed)abstract
- Here, a lead-free silver bismuth iodide (AgI/BiI3) with a crystal structure with space group R (3) over barm is investigated for use in solar cells. Devices based on the silver bismuth iodide deposited from solution on top of TiO2 and the conducting polymer poly(3-hexylthiophene-2,5-diyl) (P3HT) as a hole-transport layer are prepared and the photovoltaic performance is very promising with a power conversion efficiency over 2%, which is higher than the performance of previously reported bismuth-halide materials for solar cells. Photocurrent generation is observed between 350 and 700 nm, and the maximum external quantum efficiency is around 45%. The results are compared to solar cells based on the previously reported material AgBi2I7, and we observe a clearly higher performance for the devices with the new silver and bismuth iodides composition and different crystal structure. The X-ray diffraction spectrum of the most efficient silver bismuth iodide material shows a hexagonal crystal structure with space group R (3) over barm, and from the light absorption spectrum we obtain an indirect band gap energy of 1.62 eV and a direct band gap energy of 1.85 eV. This report shows the possibility for finding new structures of metal-halides efficient in solar cells and points out new directions for further exploration of lead-free metal-halide solar cells.
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| 10. |
- Zhu, Huimin
(author)
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Lead-free Metal Halide based Solar Cells
- 2019
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Doctoral thesis (other academic/artistic)abstract
- Lead-halide perovskites have recently appeared as very promising materials for solar cells. However, their stability and toxicity may be limiting factors for their application. Therefore, to find new low toxic and high stability light harvesters may be necessary for overcoming the challenges of perovskite solar cells. The overall aim of this thesis is to explore new low toxic light harvesters and to investigate their possibility for application of solar cells. The focus in the thesis is on bismuth halide-based light harvesters, which show high light absorption coefficient and promising photovoltaic performance. Specifically, the investigated materials are different compositions of metal halides in which silver, Ag or cesium, Cs, are combined with bismuth, Bi, or antimony, Sb and the halides iodide, I, or bromide, Br. All of the systems show very promising optical performances, however, their photovoltaic performances are still low, which is partially due to the recombination and defects issues, etc. Through adjusting the elemental compositions by mixing Bi/Sb or I/Br the optical properties were tuned. By varying fabrication conditions or devices architectures, the results in this thesis also show that all the low toxic light harvesters works in solar cells, which possibly can be utilized in future photovoltaics.
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| 11. |
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| 12. |
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| 13. |
- Zhu, Huimin, et al.
(author)
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The Effect of Dopant-Free Hole-Transport Polymers on Charge Generation and Recombination in Cesium-Bismuth-Iodide Solar Cells
- 2018
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In: ChemSusChem. - : Wiley-VCH Verlagsgesellschaft. - 1864-5631 .- 1864-564X. ; 11:6, s. 1114-1120
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Journal article (peer-reviewed)abstract
- The photovoltaic characteristics of CsBi3I10-based solar cells with three dopant-free hole-conducting polymers are investigated. The effect on charge generation and charge recombination in the solar cells using the different polymers is studied and the results indicate that the choice of polymer strongly affects the device properties. Interestingly, for the solar cell with poly[[2,3-bis(3-octyloxyphenyl)-5,8-quinoxalinediyl]-2,5-thiophenediyl] (TQ1), the photon-to-current conversion spectrum is highly improved in the red wavelength region, suggesting that the polymer also contributes to the photocurrent generation in this case. This report provides a new direction for further optimization of Bi-halide solar cells by using dopant-free hole-transporting polymers and shows that the energy levels and the interaction between the Bi-halide and the conducting polymers are very important for solar cell performance.
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| 14. |
- Zhu, Huimin, et al.
(author)
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Tuning the Bandgap in Silver Bismuth Iodide Materials by Partly Substituting Bismuth with Antimony for Improved Solar Cell Performance
- 2020
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In: ACS Applied Energy Materials. - : American Chemical Society (ACS). - 2574-0962. ; 3:8, s. 7372-7382
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Journal article (peer-reviewed)abstract
- Silver bismuth iodide (Ag–Bi–I) light absorbers are interesting candidates as lead-free and low-toxic metal-halide materials for solar cell applications. In this work, the partial exchange of bismuth, Bi, with antimony, Sb, is investigated in samples prepared from a solution targeting stoichiometry AgBi2I7. Samples with a gradually increased exchange of Bi by Sb are prepared and light absorption measurements show that the absorption edge is gradually blue-shifted with increasing the amount of Sb. This trend in the shift in combination with the X-ray diffraction and X-ray photoelectron spectroscopy measurements, suggest that new materials with a mixture of Sb and Bi are formed. The density functional theory based electronic structure calculations reproduce the trend observed in the experiments when including spin–orbit coupling, which indicates the importance of relativistic effects in these materials. X-ray photoelectron spectroscopy is used to characterize the materials, and confirms the exchange of Bi to Sb in the samples. When Sb is included in the material, the grain size changes between 50 and 200 nm and the solar cell performance also changes. An optimal power conversion efficiency with excellent reproducibility and stability is obtained for a solar cell with the ratio of Sb/Bi equal to 3.
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