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[IEEE 2019 18th International Conference on Optical Communications and Networks (ICOCN) - Huangshan, China (2019.8.5-2019.8.8)] 2019 18th International Conference on Optical Communications and Networks (ICOCN) - Unraveling the Moisture-induced Decomposition Mechanism of Red-Emitting Perovskite CsPbBrI <sub/>2</sub> Nanocrystals and Enhancing their Stability through Copper(II) Substitution
摘要： The red-Emitting perovskite CsPb(BrxI1-x)3 (0<x<1) nanocrystals (NCs) is hindered because of their low structural stability, and the moisture-induced degradation pathways of these red-Emitting perovskite are not well-defined. In the present work, we show that the moisture-induced degradation of CsPbBrI2 NCs spontaneously forms CsPbBr3 (α) and CsPbI3(δ) and other decomposition products. On the other hand, highly stable and luminescent red perovskite CsPbBrI2 NCs were achieved through copper substitution and halide rich passivation strategy. We demonstrated that the incorporation of Cu2+ ions can enhance formation energy, causing a slight lattice contraction, and hence stabilize the cubic phase of these NCs. Cu2+-substituted CsPbBrI2 NCs with higher luminescence were synthesized in a halide-rich passivation method. The highly stable and luminescent Cu2+-substituted CsPbBrI2 NCs can function well as efficient light emitters toward fabrication of the high-performance red perovskite LEDs.
关键词： perovskite nanocrystals,stability,CsPbBrI2,copper-substitution,light-emitting diodes
更新于2025-09-12 10:27:22
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TaS <sub/>2</sub> Back Contact Improving Oxide-Converted Cu <sub/>2</sub> BaSnS <sub/>4</sub> Solar Cells
摘要： Solar cells based on the wide band-gap Cu2BaSnS4 (CBTS) photoabsorber have achieved open circuit voltages up to 1.1 V over a short development period, making CBTS an attractive material for tandem photovoltaic and photoelectrochemical cells. In this work, we explore an alternative CBTS growth route based on oxide precursors, and we propose TaS2 as an alternative back contact material to the commonly used Mo/MoS2. The oxide precursor route does not require higher sulfurization temperatures than other more common fabrication routes, and it yields CBTS films with negligible Stokes shift between photoluminescence maximum and band gap energy, while at the same time avoiding sulfur contamination of vacuum systems. The high work-function metallic TaS2 compound is selected as a prospective hole-selective contact, which could also prevent the losses associated with carrier transport across the semiconducting MoS2 layer. By comparing CBTS solar cells with Mo and TaS2 back contacts, the latter shows a significantly lower series resistance, resulting in a 10% relative efficiency improvement. Finally, we fabricate a proof-of-concept monolithic CBTS/Si tandem cell using a thin Ti(O,N) interlayer intended both as a diffusion barrier and as a recombination layer between the two subcells.
关键词： wide band gap absorber,back contact,kesterite,cation substitution,tandem solar cell,silicon,TaS2,sputtering
更新于2025-09-12 10:27:22
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Small Band gap Boron Dipyrromethene-Based Conjugated Polymers for All-Polymer Solar Cells: The Effect of Methyl Units
摘要： Naphthalene diimide (NDI)-based conjugated polymers have been widely used as the nonfullerene electron acceptor for all-polymer solar cells (all-PSCs), but their low absorption coefficient in the near-infrared (NIR) region severely limits the light harvesting ability in solar cells and hence lowers their photovoltaic performance. In this work, two narrow band gap donor?acceptor conjugated polymers based on boron dipyrromethene (BODIPY) as the electron-deficient unit were developed as the electron donor to combine with a NDI-polymer acceptor in order to significantly improve the photoresponse in the NIR region. More importantly, we found that methyl substitution on the BODIPY segment played an important role in charge transport in these polymers. When methyl units were attached to the α-position of BODIPY, the polymer PMBBDT exhibited high-lying energy levels, improved crystallinity, and dramatically high hole mobility compared to the polymer PBBDT without methyl substitution. Consequently, the power conversion efficiencies (PCEs) could be enhanced from 0.32% for PBBDT- to 5.8% for PMBBDT-based all-PSCs, and the photoresponse covered from 300 to 900 nm. Our results demonstrate that methyl-substituted BODIPY-based conjugated polymers are promising candidates to solve the NIR absorption issue in NDI polymers and, therefore, can be potentially used to further boost the PCEs of all-PSCs similar with organic solar cells based on NIR-fused ring electron acceptors.
关键词： Boron dipyrromethene,Methyl substitution,Conjugated polymers,Near-infrared absorption,All-polymer solar cells
更新于2025-09-11 14:15:04
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Solution-Processed Ultrahigh Detectivity Photodetectors by Hybrid Perovskite Incorporated with Heterovalent Neodymium Cations
摘要： Hybrid perovskite materials have drawn a remarkable attention for approaching high-performance photovoltaics owing to their superior optoelectronic properties. But most of research studies focused on the pristine hybrid perovskite CH3NH3PbI3. In this study, we utilize a newly developed CH3NH3PbI3:xNd3+ (x = 0.5 mol %) thin film, where Pb2+ is partially substituted by a heterovalent Nd3+ cation, as the photoactive layer for solution-processed perovskite photodetectors. It is found that the resultant CH3NH3PbI3:xNd3+ (x = 0.5 mol %) thin film possesses superior thin film morphology, enhanced and balanced charge carrier mobilities, and suppressed trap density, resulting in enhanced photocurrent and reduced dark current for perovskite photodetectors by the CH3NH3PbI3:xNd3+ (x = 0.5 mol %) thin film. Thus, operated at room temperature, solution-processed perovskite photodetectors exhibit over 1014 cm Hz1/2 W?1 photodetectivity in a spectrum range from 350 to 800 nm, a linear dynamic range over 100 dB, and fast response time. All these results indicate that high-performance solution-processed perovskite photodetectors can be realized by novel hybrid perovskite materials, where Pb2+ is partially substituted by heterovalent Nd3+ cations.
关键词： solution-processed,neodymium cations,heterovalent substitution,photodetectors,hybrid perovskite
更新于2025-09-11 14:15:04
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Wide band-gap Cu <sub/>2</sub> SrSnS <sub/>4</sub> solar cells from oxide precursors
摘要： Recent progress in the efficiency of Cu2ZnSnS4 (CZTS) solar cells has been relatively slow due to severe bulk band tailing issues that have proven difficult to resolve. Band tails in CZTS are caused by defect-related potential fluctuations, as diagnosed by the large shift between the CZTS band gap and its photoluminescence (PL) peak. In this work, we demonstrate that the PL-band gap shift can be decreased roughly by a factor of 5 when Zn is replaced by the heavier cation Sr. The resulting Cu2SrSnS4 compound is of considerable interest for photovoltaics due to its sharp band edges and suitable band gap (1.95-1.98 eV) for a top absorber in tandem cells. Trigonal CSTS thin films are synthesized in this work by sulfurization of strongly Cu-poor co-sputtered Cu2SrSnO4 precursors. The first functioning CSTS solar cells are demonstrated, even though the very high conduction band of CSTS implies that the typical CdS/ZnO electron contact of CZTS solar cells must be redesigned to avoid large voltage losses.
关键词： tail states,tandem solar cell,sputtering,wide band-gap absorber,Kesterite,cation substitution,potential fluctuations
更新于2025-09-11 14:15:04
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Charge Dynamics and Metal–Insulator Transition in Perovskite SrIr <sub/>1?</sub><i> <sub/>x</sub></i> Sn <i> <sub/>x</sub></i> O <sub/>3</sub>
摘要： We investigate the variation of charge dynamics upon the metal–insulator transition for perovskite SrIr1?xSnxO3 by employing the optical spectroscopy. The Dirac semimetal of SrIrO3 turns into the antiferromagnetic insulator with a gap of 0.1 eV by the Sn-substitution, accompanying the reconstruction of electronic structure on an energy scale of 1 eV. The spectral intensity of optical excitation between Je? = 1=2-orbitals is signi?cantly reduced with increasing x, while that between the Je? = 3=2- and 1=2-orbital shows merely moderate x-dependence. We anticipate that the substituted Sn signi?cantly renormalizes the e?ective bandwidth of Je? = 1=2-orbital while modestly changing the Je? = 3=2-orbital.
关键词： charge dynamics,optical spectroscopy,electronic structure,Je? = 3=2-orbital,perovskite,metal–insulator transition,Dirac semimetal,Je? = 1=2-orbitals,SrIr1?xSnxO3,antiferromagnetic insulator,Sn-substitution
更新于2025-09-10 09:29:36
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Enhancing saturation magnetization of Mg ferrite nanoparticles for better magnetic recoverable photocatalyst
摘要： Simple combustion route was implemented for the preparation of Mo-substituted magnesium ferrite nanoparticles; MgFe2?2xMoxO4 (x = 0.0, 0.1, 0.2 and 0.3). Samples, with x = 0.0, 0.1 and 0.2, revealed only the cubic spinel ferrite phase. Sample with x = 0.3 showed very small amount of FeMoO4, beside MgFe2O4. The lattice parameter diminished with increasing molybdenum contents to x = 0.1, then increased at x ≥ 0.2. The saturation magnetization (Ms) increased from 15.65 to 32.05 emu/g with low level of Mo6+ substitution (x = 0.1), then declined with x > 0.1. This is the first investigation to report Ms of Mg ferrite nanoparticles higher than its bulk value. The change in magnetic properties is correlated with cation distribution between tetrahedral sites (A) and octahedral sites (B). Mo6+ replaced the Fe3+ position in the tetrahedral A-sites for x = 0.1. In samples with x ≥ 0.2, Mo6+ occupied both A-sites and B-sites. Mo substitution decreased the crystallite size and increased the microstrain. Mo substitution in MgFe2O4 enhanced the photocatalytic action compared to bare MgFe2O4. The enhancement was due to the increase in structure defect that inhibits the electrons–holes recombination as well as the increase in surface area.
关键词： photocatalytic activity,Mg ferrite nanoparticles,Mo substitution,saturation magnetization
更新于2025-09-09 09:28:46
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Time-resolved structure analysis of piezoelectric crystals by X-ray diffraction under alternating electric field
摘要： Rare-earth substitution effects on atomic motions in resonantly vibrating piezoelectric oscillators of langasite-type crystals, namely, La3Ga5SiO14 (LGS) and Nd3Ga5SiO14 (NGS), are revealed by time-resolved X-ray crystal structure analysis under alternating electric fields. Deformations of Ga–O–Ga and Ga–O–Ga/Si bond angles accompanying deformations of RE–O (RE: La or Nd) bond lengths found in LGS are suppressed in NGS. Alternatively, rigid GaO6 octahedra are deformed in NGS. The decreases in RE–O bond lengths and Ga–O–Ga and Ga–O–Ga/Si bond angles caused by the substitution of La by Nd would make the bond lengths and angles more difficult to deform under electric fields; hence, the piezoelectric constants of NGS are smaller than those of LGS.
关键词： rare-earth substitution,piezoelectric crystals,alternating electric field,X-ray diffraction,time-resolved structure analysis
更新于2025-09-09 09:28:46
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Lead‐Free Semiconductors: Soft Chemistry, Dimensionality Control, and Manganese‐Doping of Germanium Halide Perovskites
摘要： Lead halide perovskites have drawn enormous interest due to their exceptional photovoltaic and optoelectronic properties. However, the toxic heavy metal lead is harmful to humans and the environment resulting in a need for strategies to replace this toxic element. Herein, we report a facile aqueous synthesis of CsGeX3 (X = I, Br) perovskite nanocrystals with size control achieved by varying the cysteammonium halide ligand concentration. We observe a variety of morphologies including pyramidal, hexagonal, and spheroidal. CsGeX3 nanocrystals undergo a lattice expansion due to partial replacement of Cs+ with larger cysteNH3+ cations into the lattice. We successfully dope Mn2+ into the CsGeX3 lattice for the first time with incorporation up to 29% in bulk and 16% in nano samples. XRD peak shifts and EPR hyperfine splitting strongly indicate that Mn2+ is doped into the lattice. Our results introduce a new member to the lead-free halide perovskite family and set the fundamental stage for their use in optoelectronic devices.
关键词： Germanium Halide Perovskites,Manganese(II) Doping,Perovskite Phases,Lead Substitution,Perovskite Nanocrystals
更新于2025-09-09 09:28:46
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Eu3+-doped Sr2(Al1?xMgx)(Al1?xSi1+x)O7 phosphors: electronic, crystal structures and photoluminescence properties
摘要： The union of chemical compositions substitution and spectral controlling is of importance for the discovery of new materials or the implementation of properties optimization. In this work, we employed an effective strategy to regulate crystal structures by chemical unit co-substitution. We applied this strategy to Eu3+-doped Sr2(Al1?xMgx)(Al1?xSi1+x)O7 (0 ≤ x ≤ 1) solid solution phosphor, which was successfully synthesized by high temperature solid state reaction. The crystal structure remained the same group, P-421m, with controlling chemical compositions. The excitation peaks shifted between 263 and 270 nm and emission peaks shifted between 612 and 614 nm with a decreasing Stocks shift in overall tendency. The shift trend was clarified by Crystal Field Theory. The energy band structure and density of states of Sr2Al2SiO7 and Sr2MgSi2O7 were calculated by Density Functional Theory using the generalized gradient approximation. The band gap was also analyzed by diffuse reflectance spectrum as a contrast. The morphology was characterized by field emission scanning electron microscopy. Furthermore, the photoluminescence color of phosphors could be tuned from yellow to orange.
关键词： crystal structure,chemical unit co-substitution,phosphors,photoluminescence,energy band structure
更新于2025-09-09 09:28:46