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1. Ligand-mediated synthesis of chemically tailored two-dimensional all-inorganic perovskite nanoplatelets under ambient conditions

   https://doi.org/10.1039/D1TC02931B  

   Davis, Andrew H. ; Li, Shuya ; Lin, Hanjie ; Chu, Chun ; Franck, John M. ; Leem, Gyu ; Maye, Mathew M. ; Zheng, Weiwei ( October 2021 , Journal of Materials Chemistry C)

   All-inorganic halide perovskite nanocrystals (NCs) offer impressive optoelectronic properties for light harvesting, energy conversion, and photoredox applications, with two-dimensional (2D) perovskite NCs further increasing these prospects due to their improved photoluminescence (PL) tuneability, impressive color purity, high in-plane charge transport, and large lateral dimensions which is advantageous for device integration. However, the synthesis of 2D perovskites is still challenging, especially toward large-scale applications. In this study, through the control of surface ligand composition and concentration of a mixture of short (octanoic acid and octylamine, 8-carbon chain) and long (oleic acid and oleylamine, 18-carbon chain) ligands, we have developed an extremely facile ligand-mediated synthesis of 2D CsPbX 3 (X = Cl, Br, or mixture thereof) nanoplatelets (NPLs) at room temperature in an open vessel. In addition, the developed method is highly versatile and can be applied to synthesize Mn-doped CsPbX 3 NPLs, showing a systematic increase in the total PL quantum yield (QY) and the Mn-dopant emission around 600 nm with increasing Mn and Cl concentrations. The reaction occurs in toluene by the introduction of CsX, PbX 2 , and MnX 2 precursors under ambient conditions, which requires no harsh acids, avoids excessive lead waste, little thermal energy input, and ismore »potentially scalable toward industrial applications.« less
2. Detailed-balance analysis of Yb ³⁺ :CsPb(Cl _1−x Br _x ) ₃ quantum-cutting layers for high-efficiency photovoltaics under real-world conditions

   https://doi.org/10.1039/c9ee01493d  

   Crane, Matthew J. ; Kroupa, Daniel M. ; Gamelin, Daniel R. ( January 2019 , Energy & Environmental Science)

   Yb 3+ -Doped lead-halide perovskites (Yb 3+ :CsPb(Cl 1−x Br x ) 3 ) have emerged as unique materials combining strong, tunable broadband absorption with near-infrared photoluminescence quantum yields (PLQYs) approaching 200% at ambient temperature. These remarkable properties make Yb 3+ :CsPb(Cl 1−x Br x ) 3 an extremely promising candidate for spectral shaping in high-efficiency photovoltaic devices. Previous theoretical assessments of such “downconversion” devices have predicted single-junction efficiencies up to 40%, but have been highly idealized. Real materials like Yb 3+ :CsPb(Cl 1−x Br x ) 3 have practical limitations such as constrained band-gap and PL energies, non-directional emission, and an excitation-power-dependent PLQY. Hence, it is unclear whether Yb 3+ :CsPb(Cl 1−x Br x ) 3 , or any other non-ideal quantum-cutting material, can indeed boost the efficiencies of real high-performance PV. Here, we examine the thermodynamic, detailed-balance efficiency limit of Yb 3+ :CsPb(Cl 1−x Br x ) 3 on different existing PV under real-world conditions. Among these, we identify silicon heterojunction technology as very promising for achieving significant performance gains when paired with Yb 3+ :CsPb(Cl 1−x Br x ) 3 , and we predict power-conversion efficiencies of up to 32% for this combination. Surprisingly, PL saturation doesmore »not negate the improved device performance. Calculations accounting for actual hourly incident solar photon fluxes show that Yb 3+ :CsPb(Cl 1−x Br x ) 3 boosts power-conversion efficiencies at all times of day and year in two representative geographic locations. Predicted annual energy yields are comparable to those of tandem perovskite-on-silicon technologies, but without the need for current matching, tracking, or additional electrodes and inverters. In addition, we show that band-gap optimization in real quantum cutters is inherently a function of their PLQY and the ability to capture that PL. These results provide key design rules needed for development of high-efficiency quantum-cutting photovoltaic devices based on Yb 3+ :CsPb(Cl 1−x Br x ) 3 .« less
3. The impact of site selectivity and disorder on the thermoelectric properties of Yb ₂₁ Mn ₄ Sb ₁₈ solid solutions: Yb ₂₁ Mn _4−x Cd _x Sb ₁₈ and Yb _21−y Ca _y Mn ₄ Sb ₁₈

   https://doi.org/10.1039/d1ma00497b  

   He, Allan ; Cerretti, Giacomo ; Kauzlarich, Susan M. ( August 2021 , Materials Advances)

   Thermoelectric materials can convert heat into electricity. They are used to generate electricity when other power sources are not available or to increase energy efficiency by recycling waste heat. The Yb 21 Mn 4 Sb 18 phase was previously shown to have good thermoelectric performance due to its large Seebeck coefficient (∼290 μV K −1 ) and low thermal conductivity (0.4 W m −1 K −1 ). These characteristics stem respectively from the unique [Mn 4 Sb 10 ] 22− subunit and the large unit cell/site disorder inherent in this phase. The solid solutions, Yb 21 Mn 4− x Cd x Sb 18 ( x = 0, 0.5, 1.0, 1.5) and Yb 21− y Ca y Mn 4 Sb 18 ( y = 3, 6, 9, 10.5) have been prepared, their structures characterized and thermoelectric properties from room temperature to 800 K measured. A detailed look into the structural disorder for the Cd and Ca solid solutions was performed using synchrotron powder X-ray diffraction and pair distribution function methods and shows that these are highly disordered structures. The substitution of Cd gives rise to more metallic behavior whereas Ca substitution results in high resistivity. As both Cd and Ca aremore »isoelectronic substitutions, the changes in properties are attributed to changes in the electronic structure. Both solid solutions show that the thermal conductivities remain extremely low (∼0.4 W m −1 K −1 ) and that the Seebeck coefficients remain high (>200 μV K −1 ). The temperature dependence of the carrier mobility with increased Ca substitution, changing from approximately T −1 to T −0.5 , suggests that another scattering mechanism is being introduced. As the bonding changes from polar covalent with Yb to ionic for Ca, polar optical phonon scattering becomes the dominant mechanism. Experimental studies of the Cd solid solutions result in a max zT of ∼1 at 800 K and, more importantly for application purposes, a ZT avg ∼ 0.6 from 300 K to 800 K.« less
4. Effect of R-site element on crystalline phase and thermal stability of Fe substituted Mn mullite-type oxides: R ₂ (Mn _1−x Fe _x ) ₄ O _10−δ (R = Y, Sm or Bi; x = 0, 0.5, 1)

   https://doi.org/10.1039/C7RA09699B  

   Thampy, Sampreetha ; Ashburn, Nickolas ; Martin, Thomas J. ; Li, Chenzhe ; Zheng, Yongping ; Chan, Julia Y. ; Cho, Kyeongjae ; Hsu, Julia W. ( January 2018 , RSC Advances)

   Combining experimental and theoretical studies, we investigate the role of R-site (R = Y, Sm, Bi) element on the phase formation and thermal stability of R 2 (Mn 1−x Fe x ) 4 O 10−δ ( x = 0, 0.5, 1) mullite-type oxides. Our results show a distinct R-site dependent phase behavior for mullite-type oxides as Fe is substituted for Mn: 100% mullite-type phase was formed in (Y, Sm, Bi) 2 Mn 4 O 10 ; 55% and 18% of (Y, Sm) 2 Mn 2 Fe 2 O 10−δ was found when R = Y and Sm, respectively, for equal Fe and Mn molar concentrations in the reactants, whereas Bi formed 54% O10- and 42% O9-mixed mullite-type phases. Furthermore, when the reactants contain 100% Fe, no mullite-type phase was formed for R = Y and Sm, but a sub-group transition to Bi 2 Fe 4 O 9 O9-phase was found for R = Bi. Thermogravimetric analysis and density functional theory (DFT) calculation results show a decreasing thermal stability in O10-type structure with increasing Fe incorporation; for example, the decomposition temperature is 1142 K for Bi 2 Mn 2 Fe 2 O 10−δ vs. 1217 K for Bi 2 Mn 4more »O 10 . On the other hand, Bi 2 Fe 4 O 9 O9-type structure is found to be thermally stable up to 1227 K. These findings are explained by electronic structure calculations: (1) as Fe concentration increases, Jahn–Teller distortion results in mid band-gap empty states from unstable Fe 4+ occupied octahedra, which is responsible for the decrease in O10 structure stability; (2) the directional sp orbital hybridization unique to Bi effectively stabilizes the mullite-type structure as Fe replaces Mn.« less
5. Synthesis and Characterization of SrFe _x Mn _1–x (O,F) _3−δ Oxide (δ = 0 and 0.5) and Oxyfluoride Perovskite Films

   https://doi.org/10.1021/acs.inorgchem.0c01148  

   Wang, Jiayi ; Lefler, Benjamin M. ; May, Steven J. ( July 2020 , Inorganic Chemistry)

   We report the synthesis and characterization of as-grown SrFexMn1-xO2.5 epitaxial films, which were also subjected to post-growth oxidation and topotactic fluorination to obtain SrFexMn1-xO3 and SrFexMn1-xO(2.5-d)Fg films. We show how both the B-site cation and anion composition influence the structural, electronic, and optical properties of this family of perovskite materials. The Fe substitution of Mn in SrMnO2.5 gradually expands the c-axis parameter, as indicated by X-ray diffraction. With increasing x, the F content incorporated under identical fluorination conditions increases, reaching its maximum in SrFeO(2.5-d)Fg. In the compounds with mixed B-site occupation, the Fe 2p photoemission peaks are shifted upon fluorination while the Mn 2p peaks are not, suggesting inductive effects lead to asymmetric responses in how F alters the Mn and Fe bonds. Electronic transport measurements reveal all compounds are insulators, with the exception of SrFeO3, and demonstrate that fluorination increases resistivity for all values of x. Optical absorption spectra in the SrFexMn1-xO2.5 and SrFexMn1-xO3 films evolve systematically as a function of x, consistent with a physical scenario in which optical changes with Fe substitution arise from a linear combination of Mn and Fe 3d bands within the electronic structure. In contrast, the F incorporation induces non-linear changes to themore »optical response, suggesting a more complex impact on the electronic structure in materials with concurrent B-site and anion site substitution.« less