The thermal stability of luminescence is very critical for white light-emitting diodes. However, it is a continuous challenge to improve the thermal stability of red phosphors. In this study, Sm3+ and Eu3+ codoped SrBi2B2O7 was synthesized by a high temperature solid state reaction method. It was found that the thermal stability of the synthesized phosphors was improved as Sm3+ was used as the sensitizer for Eu3+ doped into SrBi2B2O7. Combined with a local crystal environment study and the first-principles calculations, the origin of the improvement of this thermal stability was studied in detail. The doped Sm3+ and Eu3+ ions were inclined to occupy Bi(1) (6c) and Bi(2) (6c) sites simultaneously and the crystal structure of the SrBi2B2O7:Sm3+, Eu3+ was more compact at high temperature than that at room temperature. Thus, the defect formation energy was very low in the Sm3+ and Eu3+ codoped SrBi2B2O7 phosphor, which is the main reason to improve the thermal stability with Sm3+ and Eu3+ codoped into SrBi2B2O7. This study provides a new idea for developing a new method to improve the thermal stability of red-emitting phosphors.

It is a challenge to fabricate high quality Cu2ZnSnSe4 (CZTSe) film with low Cu content (Cu/(Zn + Sn) < 0.8). In this work, the growth mechanisms of CZTSe films under different Se vapor composition are investigated by DC-sputtering and a postselenization approach. The composition of Se vapor has important influence on the compactability of the films and the diffusion of elements in the CZTSe films. By adjusting the composition of Se vapor during the selenization process, an optimized two step selenization process is proposed and highly crystallized CZTSe film with low Cu content (Cu/(Zn + Sn) = 0.75) is obtained. Further study of the effect of Cu content on the morphology and photovoltaic performance of the corresponding CZTSe solar cells has shown that the roughness of the CZTSe absorber film increases when Cu content decreases. As a consequence, the reflection loss of CZTSe solar cells reduces dramatically and the short circuit current density of the cells improve from 34.7 mA/cm2 for Cu/(Zn + Sn) = 0.88 to 38.5 mA/cm2 for Cu/(Zn + Sn) = 0.75. In addition, the CZTSe solar cells with low Cu content show longer minority carrier lifetime and higher open circuit voltage than the high Cu content devices. A champion performance CZTSe solar cell with 10.4% efficiency is fabricated with Cu/(Zn + Sn) = 0.75 in the CZTSe film without antireflection coating.Keywords: Cu content; CZTSe; selenization; SnSe2 phase; textured surface

•Flat and compact Cu film was deposited on Mo by PC electrodeposition method.•Cu film was deposited from CuSO4 solution without additives.•Concentration polarization was controlled successfully.•10.39% CIGS and 7.83% CZTSe solar cells were fabricated.The issues of rough surface morphology and the incorporated additives of the electro-deposited Cu layers, which exists in electrodeposition-based processes, is one of the major obstacles to improve the efficiency of Cu(In,Ga)Se2 (CIGSe) and Cu2ZnSnSe4 (CZTSe) solar cells. In this study, the pulse current electro-deposition method is employed to deposit smooth Cu film on Mo substrate in CuSO4 solution without any additives. Grain size of the deposited Cu film is decreased by high cathode polarization successfully. And the concentration polarization, which results from high pulse current density, is controlled successfully by adjusting the pulse frequency. Flat Cu film with smooth surface and compact structure is deposited as pulse current density @ 62.5 mA cm−2, pulse frequency @100,000 Hz, and duty cycle @ 25%. CIGSe and CZTSe absorber films with flat surface and uniform elemental distribution are prepared by selenizing the stacking metal layers electro-deposited by pulse current method. Finally, the CIGSe and CZTSe solar cells with conversion efficiency of 10.39% and 7.83% respectively are fabricated based on the smooth Cu films, which are better than the solar cells fabricated by the rough Cu film deposited by direct current electro-deposition method.

•Beyond 10% efficiency CZTSSe solar cells were fabricated using sputtering method.•High content of Zn lead to high carrier concentration of CZTSSe solar cells.•Depletion region of CZTSSe solar cell increases with the decrease of Zn content.•Wide depletion region is benefit to the collection of photo generated carriers.High performance Cu2ZnSn(S,Se)4 (CZTSSe) solar cells are fabricated by selenization of the precursor films of Mo/Sn/Cu/ZnS/Sn/ZnS/Cu deposited by magnetron sputtering. The investigation of the solar cells with different Zn/Sn ratio in CZTSSe film discloses that the charge carrier concentration and depletion region width of the device is very sensitive to Zn/Sn ratio of CZTSSe layer. The CZTSSe film with Zn/Sn=1.05 has lower carrier density (5.0×1015 cm−3), which is half of the cell with Zn/Sn=1.12, whereas the depletion region at the CdS/CZTSSe hetero-junction interface of the former (200–250 nm) is 100 nm longer than the latter. As a result, better collection of photo-generated charge carrier is found with the cell with longer Wd in the longer wavelength region above 800 nm. Therefore, the average power conversion efficiency is increased from 6.53% to 9.16% with enlarged depletion region width, and the best performance with 10.2% efficiency is achieved.

α-NaSrBO3 is an excellent phosphor host for phosphor-converted white light-emitting diode (w-LED) application with very interesting properties. However, it undergoes a phase transformation to β-NaSrBO3 at the LED working temperature. In this study, the high-temperature phase β-NaSrBO3 was stabilized to room temperature by introducing Na+ and Ce3+ via a high-temperature solid-state reaction method. The crystal structure of β-NaSrBO3 was determined from the powder X-ray diffraction data. It crystallizes in space group P21/c with the following lattice parameters: a = 6.06214(8) Å, b = 5.41005(7) Å, c = 9.1468(1) Å, β = 102.116(1)°, and V = 293.301(7) Å3. Na and Sr sites are found to be mixed occupied by each other, and the isolated [BO3]3– anionic groups are distributed in parallel. Ce3+-activated β-NaSrBO3:Ce3+ blue-emitting phosphors were synthesized. The temperature-dependent photoluminescence spectra indicate that the thermal stability of β-NaSrBO3:Ce3+ is better than that of α-NaSrBO3:Ce3+ at the same temperature. A near-ultraviolet pumped warm w-LED with a β-NaSrBO3:0.05Ce3+ phosphor as the blue component was fabricated. The w-LED lamp after illumination at 250 mA gives chromaticity coordinates, a color rendering index, and a correlated color temperature of (0.3821, 0.3430), 92.8, and 3654 K, respectively.

•The selenized CZTSSe films show poor adhesion to the Mo substrate unless the Cu layer was stacked on the top of the film.•Stacking order of Cu–ZnS–SnS determines the orientation of crystal growth of CZTSSe (bottom-to-top or top-to-bottom).•A thin film solar cell with 3.35% conversion efficiency is obtained using Cu/SnS/ZnS/Mo precursor.Sputtering and subsequent sulfurization (or selenization) is one of the methods that have been extensively employed to fabricate Cu2ZnSn(S,Se)4 (CZTSSe) thin films. However, there are limited reports on the effect of precursor stacking order of the sputtered source materials on the properties of the synthesized CZTSSe films. In this work, the morphology and crystallization process of the CZTSSe films which were prepared by selenizing Cu–ZnS–SnS precursor layers with different stacking sequences and the adhesion property between the as-synthesized CZTSSe layer and Mo substrate have been thoroughly investigated. It has been found that the growth of CZTSSe material and the morphology of the film strongly depend on the location of Cu layer in the precursor film. The formation of CZTSSe starts from the diffusion of Cu–Se to Sn(S,Se) layer to form Cu–Sn–(S,Se) compound, followed by the reaction with Zn(S,Se). The investigation of the morphology of the CZTSSe films has shown that large grains are formed in the film with the precursor stacking order of Mo/SnS/ZnS/Cu, which is attributed to a bottom-to-top growth mechanism. In contrast, the film made from a precursor with a stacking sequence of Mo/ZnS/SnS/Cu is mainly consisted of small grains due to a top-to-bottom growth mechanism. The best CZTSSe solar cell with energy conversion efficiency of 3.35% has been achieved with the selenized Mo/ZnS/SnS/Cu film, which is attributed to a good contact between the absorber layer and the Mo substrate.

Mn2+-activated red phosphor α-LiZnBO3:Mn2+ was synthesized by solid state reaction. ESR spectra prove that the doped ions are Mn2+. The doped Mn2+ ion is inclined to occupy Zn2+ site, which is a tetrahedral coordination. The diffuse reflection spectra indicate that α-LiZnBO3:Mn2+ has strong absorption in the range of 400–450 nm. Excited at 431 nm, an abnormal red emission band in the wavelength of 550–800 nm is observed, which is because of the strong crystal field induced by the distorted tetrahedral. The emission bands are centered at 647 nm, regardless of the excitation wavelength and Mn2+ doping concentration. The temperature-dependent PL results reveal that α-LiZnBO3:Mn2+ is thermally stable but the emission peak moves to shorter wavelength as temperature increases because of the decrease of the crystal field.

•The adhension between AlN film and Mo are verygood.•AlN film can be effectively used as the barrier of flexible CIGS solar cell on SS substrate.•AlN film is suitable as the insulation barrier of flexible CIGS solar cell on SS substrate.The AlN film deposited by DC magnetron sputtering on stainless steel (SS) foils was used as the barrier in flexible Cu(In,Ga)Se2 (CIGS) solar cells on stainless steel foil and characterized comprehensively by X-ray diffraction (XRD), scanning electron microscopy (SEM), I–V, and QE measurements study. The study of AlN as insulation barrier in the flexible CIGS solar cell showed that the adhesion strength between the SS foil and the deposited AlN film was very strong even after annealing at high temperature at 530 °C. More importantly, a high resistance of over 10 MΩ was remained with the film with thickness of around 200 nm after annealing. This indicates that the AlN film is suitable as an effective insulation barrier in flexible CIGS solar cells based on SS foil. In addition, the XRD and SEM results showed that the AlN film did not influence the crystal structure of the Mo film which was deposited upon the AlN layer and used as the electrical contact in CIGS solar cells. It was found that the AlN film contributed to an improved crystallinity of the Mo contact layer compared to the bare SS foil. The combined results of secondary ion mass spectrometry, I–V and EQE measurements of the corresponding flexible CIGS solar cells confirmed that 1 μm-thick AlN film could be used as an efficient barrier layer in CIGS solar cells on SS foil.

•New red-emitting ZnBi2B2O7:xEu3+ phosphors excited by near ultraviolet light were synthesized.•The doped Eu3+ prefers to occupy Zn2+ site and there is only one-center luminescence of Eu3+ in ZnBi2B2O7 host.•CIE coordinates are very much closer to that of standard red light (0.67, 0.33).A series of Eu3+-activated red phosphors ZnBi2B2O7:xEu3+ were synthesized by high temperature solid-state reaction method. Rietveld refinement on the powder X-ray diffraction (XRD) data was performed to study the local crystal environment of Eu3+ in ZnBi2B2O7 host. The refinement results disclose that the doped Eu3+ do not change the host structure. Although two different cation sites are available, the doped Eu3+ is inclined to occupy Zn site instead of Bi site. This indicates that there is only one luminescent center when Eu3+ is doped into ZnBi2B2O7 phosphor, which is further confirmed by the luminescence properties of ZnBi2B2O7:xEu3+. The influences of the doping concentration and the excitation wavelength on the one-center luminescence of Eu3+ in ZnBi2B2O7 are discussed along with the decay characteristics. Based on the temperature-dependent PL spectra, the fast decrease of emission intensity with the increase of temperature is due to the non-radiative relaxation.

In this combined X-ray diffraction and photoluminescence study, the coordination environment of Mn2+ and the photoluminescence of single Mn2+ doped KMgBO3 phosphors were studied. Mn2+ occupies Mg2+ sites, which were coordinated by six O2−. The strong absorption of KMgBO3:Mn2+ was ascribed to the strong relaxation of spin and parity forbidden d–d transitions of Mn2+. The emission bands were centered at 636 nm, regardless of the excitation wavelength and Mn2+ doping concentration. Mn2+ activated KMgBO3 could be efficiently excited with the excitation of Mn2+ d–d transitions in the wavelength range of 300–475 nm. The red-shift of Mn2+ emission was because of the strong crystal field environment of Mn2+ afforded by KMgBO3. The potential applications of the phosphors have been pointed out based on their absorption spectra, excitation and emission spectra, thermal quenching properties, and decay properties.

A series of Dy3+-, Tm3+-, Eu3+-coactivated KSr4(BO3)3 phosphors were synthesized via a standard solid-state reaction under normal ambient air, and the emission colors could be tuned from blue to yellow and then to red, including almost all the white light region, through tuning the energy transfer. It was discovered that the energy is transferred from Tm3+ to Dy3+ by: directly observing overlap of the excitation spectrum of Dy3+ and the emission spectrum of Tm3+; the systematic relative decline and growth of emission bands of Tm3+ and Dy3+, respectively; and faster decay times of the blue emissions from energy donors. The resonance-type energy transfer from Tm3+ to Dy3+ was demonstrated to be via the dipole–quadrupole mechanism and the critical distance of energy transfer was calculated to be 20.7 Å. Rietveld refinements of the crystal structures of the products obtained from powder X-ray diffraction (XRD) elucidated a preferable occupancy in the crystal unit for the doped rare-earth cations, which well explained the formation of the Tm3+–Dy3+ close pair. By utilizing the principle of energy transfer, we have demonstrated that with appropriate tuning of activator content, KSr4(BO3)3:Dy3+,Tm3+,Eu3+ phosphors exhibit great potential for use as single-component phosphors for warm white ultraviolet light-emitting diodes (UV LEDs).

We report the first example of the preparation of an ordered hierarchical zeolitic imidazolate framework nest architecture (denoted as ZIF-GIS). ZIF-GIS (Zn(eIm)0.65(dmbIm)1.35) is a novel compound with GIS topology and has been synthesized by using complementary ligands of 2-ethylimidazole (eIm) and 5,6-dimethylbenzimidazole (dmbIm) in several solution systems. ZIF-GIS which exhibits hierarchical and nest architectures was obtained by a solvothermal approach based on the mixed solvent of aqueous ammonia (NH3·H2O) and methanol (CH3OH). The apple-like hierarchical ZIF-GIS architectures with diameters of about 2–3 μm are built from numerous nanoplates with a thickness of about 20–40 nm. The results demonstrated that the formation of ordered hierarchical and nest architectures could be ascribed to the cooperation of NH3·H2O and CH3OH. This synthesis strategy in a mixed solvent might be extended to other systems for the synthesis of hierarchical ZIF or MOF architectures.

In this combined atomic force microscopy and X-ray diffraction study, we explore the microscopic origin of the scaling properties of the growth of organic−organic heterostructures formed here by F16CoPc and diindenoperylene (DIP) molecules as representative systems for electron and hole transporting materials. We evaluate the influence of the morphological properties of the first organic layer (DIP) on further temporal evolution of the morphology and structure of F16CoPc films. From the derived scaling exponents, we conclude that the morphology evolution is dominated by mound formation. The microscopic origin of such morphology is ascribed to structural changes occurring during the first stages of F16CoPc growth as revealed by grazing incidence X-ray diffraction (GIXD). The microstructure of organic materials should be taken into account, the challenging task of modeling growing surfaces and interfaces of organic materials.

Mn2+-activated red phosphor α-LiZnBO3:Mn2+ was synthesized by solid state reaction. ESR spectra prove that the doped ions are Mn2+. The doped Mn2+ ion is inclined to occupy Zn2+ site, which is a tetrahedral coordination. The diffuse reflection spectra indicate that α-LiZnBO3:Mn2+ has strong absorption in the range of 400–450 nm. Excited at 431 nm, an abnormal red emission band in the wavelength of 550–800 nm is observed, which is because of the strong crystal field induced by the distorted tetrahedral. The emission bands are centered at 647 nm, regardless of the excitation wavelength and Mn2+ doping concentration. The temperature-dependent PL results reveal that α-LiZnBO3:Mn2+ is thermally stable but the emission peak moves to shorter wavelength as temperature increases because of the decrease of the crystal field.

A series of Dy3+-, Tm3+-, Eu3+-coactivated KSr4(BO3)3 phosphors were synthesized via a standard solid-state reaction under normal ambient air, and the emission colors could be tuned from blue to yellow and then to red, including almost all the white light region, through tuning the energy transfer. It was discovered that the energy is transferred from Tm3+ to Dy3+ by: directly observing overlap of the excitation spectrum of Dy3+ and the emission spectrum of Tm3+; the systematic relative decline and growth of emission bands of Tm3+ and Dy3+, respectively; and faster decay times of the blue emissions from energy donors. The resonance-type energy transfer from Tm3+ to Dy3+ was demonstrated to be via the dipole–quadrupole mechanism and the critical distance of energy transfer was calculated to be 20.7 Å. Rietveld refinements of the crystal structures of the products obtained from powder X-ray diffraction (XRD) elucidated a preferable occupancy in the crystal unit for the doped rare-earth cations, which well explained the formation of the Tm3+–Dy3+ close pair. By utilizing the principle of energy transfer, we have demonstrated that with appropriate tuning of activator content, KSr4(BO3)3:Dy3+,Tm3+,Eu3+ phosphors exhibit great potential for use as single-component phosphors for warm white ultraviolet light-emitting diodes (UV LEDs).

In this combined X-ray diffraction and photoluminescence study, the coordination environment of Mn2+ and the photoluminescence of single Mn2+ doped KMgBO3 phosphors were studied. Mn2+ occupies Mg2+ sites, which were coordinated by six O2−. The strong absorption of KMgBO3:Mn2+ was ascribed to the strong relaxation of spin and parity forbidden d–d transitions of Mn2+. The emission bands were centered at 636 nm, regardless of the excitation wavelength and Mn2+ doping concentration. Mn2+ activated KMgBO3 could be efficiently excited with the excitation of Mn2+ d–d transitions in the wavelength range of 300–475 nm. The red-shift of Mn2+ emission was because of the strong crystal field environment of Mn2+ afforded by KMgBO3. The potential applications of the phosphors have been pointed out based on their absorption spectra, excitation and emission spectra, thermal quenching properties, and decay properties.