Improvement of conversion efficiency of silicon solar cells using up-conversion molybdate La_2Mo_2O_9：Yb,R （R=Er, Ho） phosphors

The goal of this work was aimed to improve the power conversion efficiency of single crystalline silicon-based photovoltaic cells by using the solar spectral conversion principle, which employs an up-conversion phosphor to convert a low energy infrared photon to the more energetic visible photons to improve the spectral response. In this study, the surface of multicrystalline silicon solar cells was coated with an up-conversion molybdate phosphor to improve the spectral response of the solar cell in the near-infrared spectral range. The short circuit current (Isc), open circuit voltage (Voc), and conversion efficiency (η) of spectral conversion cells were measured. Preliminary experimental results revealed that the light conversion efficiency of a 1.5%-2.7% increase in Si-based cell was achieved.     

Solar spectral conversion based on plastic films of lanthanide-doped ionosilicas for photovoltaics:Down-shifting layers and luminescent solar concentrators

The mismatch between the photovoltaic(PV) cells absorption and the solar irradiance on earth is one of the major limitations towards more efficient PV energy conversion.This aspect was addressed by downshifting the solar irradiance on Earth through luminescent down-shifting layers based on lanthanidedoped surface-functionalized ionosilicas(ISs) embedded in poly(methyl methacrylate)(PMMA) coated on the surface of commercial Si-based PV cells.The IS-PMMA hybrid materials exhibit efficient solar radiation harvesting(spectral overlap of ～9.5 × 10~(19) photons/(s·m~2)) and conversion(quantum yield～52%).The direct solar radiation and the down-shifted radiation are partially guided and lost through total internal reflection to the layer edges being unavailable for PV conversion of the coated PV cell.By tuning the down-shifting layer thickness,it also acts as luminescent solar concentrator enabling the collection of the guided radiation by flexible PV cells applied on the borders of the down-shifting layer leading to an enhancement of the PV energy conversion from ～5%(in the case of the single-use of the luminescent down-shifting layer) to～13% comparing with the bare PV cell.The overall electrical output of the device resulted in an absolute external quantum efficiency increase of～32% for the optimized Eu~(3+)-based films in the UV spectral region(compared with the bare PV device,which is among the best values reported so far).     

Luminescent properties and application of Eu3+ -activated Gd2(MoO4)3 red-emitting phosphor with pseudo-pompon shape for solid-state lighting

Eu3+ -activated Gd2(MoO4)3 pseudo-pompon-like red-emitting phosphors were prepared by solid-state method.The structure,morphology,and luminescent properties of these powder samples were investigated by X-ray diffraction (XRD),scanning electron microscopy(SEM),and fluorescent spectrophotometry,respectively.The as-obtained phosphors were single crystalline phase with orthorhombic unit cell.The particles of the powder samples had the length of 5-12 μm and width of 3-7 μm with flake shape and large surface area,which is suitable for manufacture of white LEDs.The phosphor could be efficiently excited by the incident light of 348-425 nm,well matched with the output wavelength of near-UV (In,Ga)N chip,and re-emitted an intense red light peaking at 615 nm.By combing this phosphor with a～395 nmemitting (In,Ga)N chip,a red LED was fabricated,so that the applicability of this novel phosphor to white LEDs was confirmed.It is considered to be an efficient red-emitting conversion phosphor for solid-state lighting based on (In,Ga)N LEDs.     

Study on vacuum ultraviolet spectra of amorphous Er_2O_3 films on Si（001） substrates

Amorphous Er2O3 films have been fabricated on p-type Si(001) substrates using radio frequency magnetron sputtering technique. Vacuum ultraviolet spectra were employed to investigate the samples. An optical gap of 6.17 eV for Er2O3 films was obtained from the ab-sorption coefficient spectra. A possible reason was put forward to explain the inconsistent results about the band gap of Er2O3 in literatures. Emission spectra exhibited a strong emission band at 494 nm with the incident ultraviolet light of 249 nm. The observed high density of emission bands of Er2O3 films in the visible wavelength indicated that Er2O3 films could be used in Si solar cells for increasing conversion efficiency.     

Efficient near-infrared quantum cutting by Ce~（3＋）-Yb~（3＋） couple in GdBO_3 phosphors

Ce3+ and Yb3+ co-activated GdBO3 phosphors were prepared by a conventional solid-state reaction method. X-ray powder diffraction, photoluminescent spectra and decay curves were used to characterize their structural and luminescent properties. An efficient near-infrared (NIR) quantum cutting (QC) from the phosphors was observed, which involved the emission of two low-energy NIR photons (around 971 nm) from an absorbed ultra-violet (UV) photon at 358 nm via a cooperative energy transfer (CET) from Ce3+ to Yb3+ ions. The theoretical quantum efficiency was calculated and the maximum efficiency approached up to 164% before reaching the critical concentration quenching threshold. Our results demonstrated that these phosphors might find potential application in improving the efficiency of silicon based solar cells.     

Synthesis,structure and NIR luminescence properties of Yb~(3+) and Bi~(3+)-activated vanadate GdVO_4

Near-infrared emission of Yb~(3+) and Bi~(3+)-co-doped GdVO_4 vanadate phosphors obtained via the modified Pechini's method was reported. The phase purity and structure of samples were characterized by X-ray powder diffraction(XRD), X-ray energy dispersion spectroscopy(EDS), scanning electron microscopy(SEM), Raman and infrared(IR) spectroscopy. Photoluminescence emission(PL) and excitation(PLE) spectra were recorded and investigated in details. Results indicated that upon near-UV excitation(340 nm) in the(Bi~(3+)-V~(5+)) charge transfer state this phosphor had a strong broad band yellow-green emission(~3P_1→~1S_0) of Bi~(3+) ions and also NIR emission(~2F_(5/2)→~2F_(7/2)) of Yb~(3+) ions in the range of 950–1050 nm, which matched well with the spectral response of the silicon-based solar cells. The decreasing Bi~(3+) emission with increasing Yb~(3+) concentration proved the occurrence of energy transfer from Bi~(3+) to Yb~(3+) ions. Results demonstrated that Yb~(3+) and Bi~(3+)-co-doped GdV O4 vanadate phosphors might act as a NIR down-conversion(DC) solar spectral converter to enhance the efficiency of the silicon-based solar cells.     

Micro-Crystalline Coatings of Co-Cr Dispersed with Y2O3 Deposited by Series Electro-Pulse Discharge

A new technique-series electro-pulse discharge (SEPD)-was developed as a kind of surface coating process. In this technique, both positive and negative poles of a pulse power were used as the depositing electrodes with the substrate alloy as an induction electrode. Micro-crystalline Co-Cr and Co-Cr dispersed with Y2O3 coatings were deposited on Fe-18Cr-SNi stainless steel surface by using Co30Cr alloy as the depositing electrodes. Oxidation at 950℃ in ambient air shows that these coatings greatly improve the oxidation resistance of the steel. The addition of dispersed Y2O3 nano-particles into the alloy coatings was found to further reduce the scaling rate and enhance the adhesion of oxide scales.     

Hierarchical porous carbon toward effective cathode in advanced zinc-cerium redox flow battery

Advanced zinc-cerium redox flow battery(ZCRFB) is a large-scale energy storage system which plays a significant role in the application of new energy sources. The requirement of superior cathode with high acitivity and fast ion diffusion is a hierarchical porous structure, which was synthesized in this work by a method in which both hard template and soft template were used. The structure and the performance of the cathode prepared here were characterized and evaluated by a variety of techniques such as scanning electron microscopy(SEM), transmission electron microscopy(TEM), X-ray photoelectron spectroscopy(XPS), cyclic voltammetry(CV), linear sweep voltammetry(LSV), and chronoamperometry(CA). There were mainly three types of pore size within the hierarchical porous carbon: 2 μm, 80 nm, and 10 nm. The charge capacity of the cell using hierarchical porous carbon(HPC) as positive electrode was obviously larger than that using carbon felt; the former was 665.5 mAh with a coulombic efficiency of 89.0% and an energy efficiency of 79.0%, whereas the latter was 611.1 mAh with a coulombic efficiency of 81.5% and an energy efficiency of 68.6%. In addition, performance of the ZCRFB using HPC as positive electrode showed a good stability over 50 cycles.These results showed that the hierarchical porous carbon was superior over the carbon felt for application in ZCRFB.     

Oxalate-assisted morphological effect of NaYF4:Yb3+,Er3+ on photoelectrochemical performance for dye-sensitized solar cells

In this study. we have employed a facile oxalate-assisted hydrothermal approach to tailor the morphology of β-NaYF_4:Er~(3+),Yb~(3+)(NYFEY) powders through the variation of the molar ratio of oxalate ions(Oxa~(2-)) and rare earth ions(RE~(3+)) in the range of 0.5:1.1:1.2:1, 5:1. and 10:1. The obtained results show that the crystallinity, particle size and upconversion luminescence intensity of the as-synthesized NYFEY particles are gradually decreased as the Oxa~(2-):RE~(3+) molar ratio increases from 0.5:1 to 10:1. For the purpose of photoelectrochemical performance evaluation,the as-synthesized NYFEY particles with different morphologies are incorporated into the nanocrystalline TiO2 films to form the multifunctional nano-and sub-micro meter composite photoanodes of dye-sensitized solar cells(DSSCs). A short-circuit current density(Jsc) of 14.26 mA/cm~2 and power conversion efficiency(PCE) of 7.31% are obtained for DSSCs prepared with hexagonal rod-like NYFEY crystals,evidencing an increase of 29.8% compared with DSSCs prepared with only TiO_2 nanoparticles. The demonstrated synthesis approach for tailoring the morphology and size of NYFEY particles and enhancing the performance of DSSCs can also be applied for other types of solar cells.     

Luminescence properties of SrB4O7：Sm^2＋ for light conversion agent

A deep red-emitting SrB4O7:Sm2+ phosphor for light conversion agent was synthesized by the conventional solid-state reaction. X-ray powder diffraction (XRD) analysis confirmed the phase formation of SrB4O 7:Sm2+ materials. Results of luminescence properties showed that the phosphor could be efficiently excited by the UV-vis light region from 250-500 nm, and it exhibited deep red (685 nm) emission corresponding to 5D0 → 7F0 transition of Sm 2+ . The critical quenching concentration of Sm 2+ in SrB4O7 :Sm 2+ phosphor was about 0.05, and the corresponding concentration quenching mechanism was verified to be the dipole-dipole interaction according to the Dexter’s theory. The decay times had few alterations with different concentrations in SrB4O7:xSm 2+ phosphor.     

Monolithic crystalline silicon solar cells with SiN_x layers doped with Tb~(3+) and Yb~(3+) rare-earth ions

In this study, we propose the fabrication of monolithic crystalline silicon solar cells with Tb~(3+) and Yb~(3+)-doped silicon nitride(SiN_x) layers by low-cost screen-printing methods. The performances of c-Si solar cells can be enhanced by rare-earth ions doped SiN_x layers via the mechanism of spectrum conversion.These SiN_x doped and codoped thin films were deposited by reactive magnetron co-sputtering and integrated as the antireflection coating layers in c-Si solar cells. The characterizations of SiN_x, SiN_x:Tb~(3+) tand SiN_x:Tb~(3+)-Yb~(3+) thin films were conducted by means of photoluminescence, Rutherford backscattering spectroscopy, Ellipsometry spectroscopy and Fourier transform infrared measurements. Their composition and refractive index was optimized to obtain good anti-reflection coating layer for c-Si solar cells.Transmission electron microscopy performs the uniform coatings on the textured emitter of c-Si solar cells. After the metallization process, we demonstrate monolithic c-Si solar cells with spectrum conversion layers, which lead to a relative increase by 1.34% in the conversion efficiency.     

Plasmon-enhanced broad-band quantum-cutting of NaBaPO4:Eu2+,Er3+ phosphors with silver nano-particles

NaBaPO₄:Eu²⁺,Er³⁺ phosphors and Ag nano-particles (NPs) were prepared by the solid-state reaction and chemical reduction method, respectively. The fluorescence spectra and decay curves demonstrate the effective energy transfer from Eu²⁺ to Er³⁺ and the existence of three-photon quantum-cutting through two-step cross-relaxation of Er³⁺. The quantum-cutting emission is peaked at 1534 nm with a broad excitation band centered at 352 nm. Plasmon-enhanced quantum-cutting of NaBaPO₄:Eu²⁺,Er³⁺ phosphors was realized by decorating Ag NPs. The largest enhancement factor is 1.395. It is hopeful to improve the photovoltaic conversion efficiency of Ge solar cells by using this phosphor.     

红色长余辉发光材料BaMg_2Si_2O_7∶Pr,Mn的制备及性质研究

采用高温固相法合成了红色长余辉材料BaMg2Si2O7∶Pr,Mn,利用X晶体衍射仪、扫描电镜、荧光光谱、热释光测量仪等对材料的性能进行了表征,结果分析证明BaMg2Si2O7∶Pr,Mn以Mn2+为发光中心,Pr3+为共激活离子,在紫外光的照射下能够得到由Mn2+的4T1(4G)→6A1(6S)跃迁产生的峰值在666nm发射峰,产生红光发射,撤离激发光源后,能够产生余辉,且余辉时间可以持续达40分钟以上,基质中存在着Pr3+→Mn2+的能量传递,能够增强其荧光发射峰强度并对余辉性能有一定促进作用。     

Synthesis and photoluminescence properties of octahedral K_2(Ge,Si)F_6:Mn~(4+) red phosphor for white LED

A novel red-emitting K_2(Ge,Si)F_6:Mn~(4+) phosphor with uniform morphology was synthesized by co-precipitation method. The pure K_2GeF_6 phase with P63 mc space group other than P3m1 space group was affirmed just by incorporation of Si in K_2GeF_6 at room temperature according to XRD characterization. SEM images showed lamellar and octahedron grain morphology for K_2GeF_6:Mn~(4+) and K_2(Ge,Si)F_6:Mn~(4+) phosphors, respectively. It was also found that the photoluminescence excitation(PLE) and photoluminescence(PL) showed slight displacement in K_2GeF_6:Mn~(4+) and K_2(Ge,Si)F_6:Mn~(4+) system. And the zero-phonon line(ZPL) of the PL spectrum of K_2GeF_6:Mn~(4+) with Si showed a strong peak. Meanwhile crystalline field surrounding Mn~(4+) changes could affect the decay time in this fluoride system. The color gamut of the LED devices based on K_2(Ge,Si)F_6:Mn~(4+) and K_2GeF_6:Mn~(4+) reached up to 94.58% NTSC(National Television Standards Committee) and 94.386% NTSC, respectively, that was much higher than that based on nitride red phosphors. All these original characteristics in K_2(Ge,Si)F_6:Mn~(4+) phosphor are desirable for potential applications as a red phosphor for improving lighting and display quality of conventional white LEDs.     

钙钛矿太阳能电池稳定性研究进展

从钙钛矿晶格结构和器件结构入手,介绍了钙钛矿电池的发展历程,总结了A位,B位及X位的组分调控方法、一步法、两步法及其他成膜方法,形貌控制方法,最后,详细讨论了钙钛矿太阳能电池稳定性的影响因素,光热湿等因素是引起钙钛矿晶体分解,导致电池性能下降的主要原因。最后,稳定性问题已经成为阻碍钙钛矿电池产业化的最大的障碍,介绍了钙钛矿太阳能电池当前稳定性问题的主要解决方案:开发更稳定的钙钛矿结构,开发用于控制晶粒生长的新添加剂,以及选择具有优异性能的空穴传输层和电子传输层。      

Moisture-induced degradation of the narrow-band red-emitting SrLiAl3N4:Eu2+ phosphor

The degradation of materials plays an important role in their application and service process. In this work, the moisture-induced degradation of SrLiAl₃N₄:Eu²⁺ (SLAN), a very promising narrow-band red-emitting phosphor, was comprehensively investigated by treating it in two different moisture conditions in order to reveal the potential mechanism and optimize the luminescence properties. The degradation rate gradually slows down with the decreasing environmental humidity indicating that water plays a key role in the degradation. Moreover, we take the other option with 100% humidity at different temperatures for rapid degradation. In the rapid degradation, the luminescence of SLAN is quenched quickly and the phase and microstructure change obviously, with the phosphor being bleached. The host turns into NH₃, Al₂O₃, Sr₃Al₂(OH)₁₂ and LiAl₂(OH)₇ finally. It is further confirmed that the rapid degradation occurs with the help of water and the phosphor is oxidized during this process.