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The progress of selenized Cu(In,Ga)Se 2 (CIGSe) solar cells is limited by low open-circuit voltage (Voc), which results from the Ga-deficient surface and undesirable bandgap profile after selenization. Controlling the Ga grading, especially on the CIGSe surface, is challenging but critical for further efficiency improvement. Here, the simple sputtering route with K incorporation is presented to engineer single- or double-graded bandgap. The K incorporation through sputtered precursors can considerably affect the Ga profile in CIGSe during selenization, essentially distinct from reported KF post-deposition treatment, in which the Ga profile keeps unchanged. Using synchrotron-based X-ray absorption spectroscopy and first-principle calculations, we verify that Ga diffusion via Cu vacancies is restrained due to the presence of K Cu defects. Therefore, by introducing a CuGa:KF surface layer on the bi-layer precursors, the surface Ga content of CIGSe is increased effectively, achieving a notch-like Ga distribution after selenization. This unique CuGa:KF layer significantly boosts the Voc and yields over 15% efficiency, even with a low reactive Se vapor for selenization. Our approach, completely compatible with the existing fabrication process, offers a new direction for engineering band structure without sulfurization. [ABSTRACT FROM AUTHOR]

Although the efficiency of Cu(In , Ga)Se 2 (CIGS) solar cells have exceeded 22% for the absorber with thickness more than 2 µm, thinning the absorber thickness has attracted attention to save the material costs of indium and gallium as well as to increase manufacturing throughput. However, a trade-off exists between efficiency and thickness of CIGS absorbers. In this work, we report a new insight to promote the efficiency of ultrathin (hundred-nanometer scale) CIGS solar cells by engineering Na-transport in a direct sputtering process with a quaternary CIGS target without post-selenization. We first demonstrate a feasibility to manipulate the preferred orientation of CIGS absorbers via controlled texture growth of the Mo underlayers. Then, we reveal that the amount of Na content within absorbers is strongly related to the preferred orientation and Cu-content of CIGS. The Cu-deficient CIGS absorbers grown on (211)-Mo underlayer show the strongest (220/204) CIGS texture and highest Na content, leading to enhanced efficiency. Through adequate Na-transport engineering and commonly used Ga gradient, we have significantly enhanced the efficiency of ultrathin (550 nm) CIGS solar cells to 10.04%. Our results unveil the key factors of Na-transport in nano-scale and provide a strategy to achieve high-efficiency ultrathin CIGS solar cells. [ABSTRACT FROM AUTHOR]

An extremely environment-friendly aqueous-ink process for Cu 2 ZnSn(S,Se) 4 (CZTSSe) fabrication is reported. The aqueous ink is composed of SnS X nanoparticles, zinc ions from zinc nitrate (Zn(NO 3 ) 2 ), and metal complex made of copper nitrate (Cu(NO 3 ) 2 ) and thioacetamide (C 2 H 5 NS). The combinations of negatively surface-charged SnS X nanoparticles and cations form electric double layers and lead to a well-mixed and dispersed aqueous CZTSSe precursor ink, which eliminates the usage of hazard solvent. The results of X-ray diffraction, Raman spectroscopy, scanning electron microscope, and auger electron spectroscopy show that the CZTSSe film possesses a single phase, good crystallinity, and uniform composition after an annealing process. A high cell efficiency of 10.05% is achieved by using this novel aqueous-ink approach. To further investigate the possible root cause of efficiency limitation, the electrical properties of CZTSSe cells are studied. The existence of deep donor defects, which results in low carrier concentration as well as collapsed short-circuit current and fill factor at low temperature, is proposed. Our proposed model suggests that the relatively deep p-type defects (Cu Zn ) as the major carrier source, the existence of deep n-type defects and short diffusion length are the key limitations for achieving high efficiency of CZTSSe solar cells. [ABSTRACT FROM AUTHOR]

Control of Se content during manufacturing process has been known to determine the efficiency of Cu(In x Ga 1− x )Se 2 (CIGS) solar cells. However, how Se is distributed in CIGS films and how Se distribution in hundred-nanometer scale affects the cell performance have not been realized due to limited spatial resolution of composition mapping technique. In this study, a promising nondestructive analysis by using field-emission electron probe microanalysis (FE-EPMA) is first demonstrated to directly probe the Se distribution within the depletion region of CIGS absorbers. We observe that Se-deficient-related defects are still exist in CIGS films even with high Se concentration but non-uniform distribution, leading to relatively low efficiency (~7%). By correlating photoluminescence spectra and conductivity mapping with composition distribution, we clarify that the uniform Se distribution is the key factor to suppress the defect formation and to enhance the p–n inversion at grain boundaries, resulting in significant efficiency boost to 12%. [ABSTRACT FROM AUTHOR]

Manipulating the nature of defects and carrier dynamics in kesterite Cu 2 ZnSnS 4 (CZTS) solar cells is challenging because of the complex behavior of defects. Among the various strategies used to reduce the defect levels, sodium-incorporated CZTS absorbers are effective and beneficial for defect passivation. In this study, we proposed a bifacial sodium-incorporated treatment (BSIT) in CZTS for the control of defect levels. The defect energy levels of the absorber measured by admittance spectroscopy decrease from 263 to 112 meV with increasing Na contents. In addition, impedance measurements of the sample after the BSIT showed an improved carrier dynamics with a prolonged minority carrier lifetime from 0.9 to 1.8 μs. This suggests that the post treatment of NaF diffused from the top and bottom surfaces of the CZTS absorbers is beneficial for carrier transport behaviors. Our results demonstrated that by manipulating the sodium content in the BSIT, defect passivation and effective reduction of carrier recombination can be attained, resulting in enhanced CZTS device performance from 4.1% to 5.6%. [ABSTRACT FROM AUTHOR]

Heavy alkali metal treatment is a key factor to approach high efficiency in Cu(In, Ga)Se 2 (CIGS) solar cells. Here, we show that the Cs-induced surface modification on CIGS thin-film solar cells, especially on grain boundary reconstruction generated from cesium fluoride post-deposition treatment (CsF-PDT). The CsInSe 2 phase can be synthesized by CsF-PDT process without extra assistant species, and specifically favors grain boundaries (GBs), which was further characterized by FE-EPMA, TEM, and SIMS analysis. The Cs-contained GBs may both create the valence-band downshift and conduction-band upward. By controlling the Cs-contained layer thickness and modifying absorber, the spike at conduction-band can be overcome by tunneling while remaining high valence-band downshift to suppress the GBs recombination. The efficiency was improved from 15.1 to 18.3% after CsF-PDT; the voltage loss of E g /q–V oc was down below 0.4 V. Those improvements are mainly contributed from the grain boundary reconstruction at the junction area using CsF-PDT to reduce the recombination. Image 1 • Non-nanopattern surface modification by CsF-PDT specializes in grain boundaries. • CsInSe 2 phase can be synthesized by CsF-PDT without extra assistant species. • Cs-contained GBs create valence-band downshift and suppress the recombination. • Cs-treatment reduces recombination through Cs-contained grain boundary. • Voltage loss below 0.4 V can be achieved by heavy alkali-treatment. [ABSTRACT FROM AUTHOR]

Abstract With the rapid growth of electronics and telecommunication industries, electromagnetic pollution is a serious concern to be addressed because it not only affects the sensitivity and performance of the devices but also affects human's health. Here, we report lightweight hybrid composite mats, having porosity around 40%, composed of amorphous carbon, zinc oxide nanorods and nickel zinc ferrite for excellent electromagnetic interference (EMI) shielding in the X-band (8.2–12.4 GHz). The vibrating sample magnetometer measurement confirmed that the saturation magnetization value (Ms) of the composite materials enhances with the weight percentage of zinc oxide nanorods-nickel zinc ferrite (ZNF) powder, which leads to enhanced magnetic loss of the electromagnetic waves. With the thickness of 1.0 mm, the total EMI shielding effectiveness of the amorphous carbon composite was measured to be 25.70 dB which was further enhanced to 53 dB by the incorporation of the ZNF powder. Such high increment is attributed to the enhanced magnetic properties, interfacial polarization and dielectric properties of the composite. The synergistic combination of the materials results in the high reflection coefficient and absorption coefficient of the composites which were measured to be ∼0.916 and ∼0.083, respectively. Thus, the composites can shield up to 99.999% power of the electromagnetic waves which is shared by the 8.394% reflection and 91.605% absorption. Moreover, the magnetic, electrical and EMI shielding properties of the composites can be tuned by controlling the amount of ZNF powder in composites. Hence, the composite mats can be suitable for applications in defense and telecommunication. Graphical abstract Image 1 [ABSTRACT FROM AUTHOR]

Al-Cu-Fe based quasicrystal thin films exhibit unique surface and mechanical properties. To better understand the formation of the quasicrystal thin films, we observe direct growth of quasicrystals, prepared in a multilayer Al-Cu-Fe thin films with subsequent heat treatment, by in-situ synchrotron x-ray diffraction and in-situ transmission electron microscopy during heating and cooling. Using these two methods, we show that the ternary phase is more thermodynamically stable compared to the binary phases at temperature higher than 470 °C during the heating process, and quasicrystal formation occurs during the cooling process, specifically at 660 °C, after the sample has reached a liquid state. To distinguish quasicrystal from approximant crystals in the obtained thin film samples, we use high resolution x-ray diffraction to analyze the sample at room temperature. We reveal that the peak broadening increases monotonically along the twofold, threefold, and fivefold high-symmetry directions with the physical scattering vector but does not have systematic dependence on the phason momentum, which suggests that the thin film sample is indeed a quasicrystal instead of approximant crystals and it is almost free of phason strain. Our study provides a complete understanding of the growth mechanism for thin film Al-Cu-Fe quasicrystals, which is of particular importance for developing versatile applications of quasicrystal thin films. Image 1 [ABSTRACT FROM AUTHOR]

We demonstrate a simple approach to fabricate Cu 2 ZnSn(S, Se) 4 (CZTSSe) absorber with increased-sulfur content surface. It is well known that the problem of interface recombination in CZTSSe solar cells is the issue for further improving efficiency. The beneficial effects of surface sulfurization were reported in Cu(In, Ga)(S, Se) 2 solar cells. However, very limited works have been reported on the effects of surface sulfurization on CZTSSe solar cells, which is a critical factor to improve the surface and achieve higher efficiency. In this work, we fabricate the CZTSSe absorber by selenizing the sulfur-containing stacked precursors. The sulfur-modified surface is achieved by introducing H 2 S gas during cooling stage of the selenization process. The effects of surface sulfurization on composition, structure, morphology, and electric properties of CZTSSe are thoroughly investigated. The open circuit voltage can be increased significantly from 312 mV (without H 2 S) to 400 mV (with H 2 S) due to the increment of front surface bandgap and reduction of interface recombination. Surface localized electric properties are improved, and interface defect density is decreased due to surface passivation by using H 2 S gas. The efficiency of CZTSSe solar cell substantially increases from 5.01% (without H 2 S) to 7.38% (with H 2 S). The proposed approach can be easily applied to various CZTSSe processes to passivate the surface and form larger surface bandgap, leading to lower interface recombination, which paves a new avenue to further improve the CZTSSe efficiency. [ABSTRACT FROM AUTHOR]

A two-step process with post-annealing of stacked precursors has been widely used for Cu 2 ZnSn(S,Se) 4 (CZTSSe) absorbers. However, no simple approach is currently available for simultaneously tuning the S/(S+Se) ratio and avoiding tin loss issue in CZTSSe films, which are critical factors to achieve high efficiency. In this work, we demonstrate by simply adding SnS powder during selenization, we can eliminate the tin loss and also control the S/(S+Se) ratio. Furthermore, we can suppress the formation of Mo(S,Se) 2 during selenization. Based on thermodynamic calculations, we propose SnS powder reacts with selenium to form SnSe and releases sulfur vapor during selenization. The Sn-contained vapor avoids tin evaporation from CZTSSe. By varying the amount of SnS powder, the partial pressure ratio of sulfur to selenium can be tuned; therefore, the film composition and band bap of CZTSSe can be changed. The presence of sulfur partial pressure also dramatically decreases the formation of Mo(S,Se) 2 during selenization. The efficiency is substantially boosted from 3.97% to 7.35% by adding SnS powder during selenization. Our approach realizes one-step sulfo-selenization, providing a general tuning knob for compositional control of CZTSSe absorbers, which shines light on various process developments of CZTSSe absorbers by post-annealing vacuum- or solution-fabricated precursors. [ABSTRACT FROM AUTHOR]

A separation process for Cu, In, Ga, and Se (CIGS)-based thin-film solar panels is proposed in this study. Initially, the separation process, by peeling off the panels in a layer-by-layer manner, was achieved by utilizing the different thermal strains of materials inside the CIGS solar panels. Subsequently, the recovery process was performed by annealing the CIGS layers for the removal of Se, and then leaching was performed with nitric acid, followed by the individual extraction of valuable metals. The pH values, concentrations of extractant, stripping agents, organic-aqueous ratios, and reaction time were investigated in detail to optimize the separation conditions for Cu, In, and Ga. First, In was extracted using di-(2-ethylhexyl) phosphoric acid into the organic phase, while Cu and Ga remained in the aqueous phase, by controlling the extraction conditions. After the extraction of In, Ga was extracted using the same extraction agent under different conditions, and nearly pure Cu remained in the residual aqueous solution. Ammonium hydroxide was added to three solutions to form metal hydroxide precipitates. Under the optimal conditions, a recovery rate of >90% could be achieved for In, Ga, and Cu. Furthermore, all as-formed hydroxides were recycled and converted into metal oxides with a purity of >99% by calcination. These findings can provide a pathway for the effective recycling and recovery of Cu, In, and Ga from waste CIGS thin-film solar panels. [Display omitted] • A facile and practical method to separate and recover valuable metals respectively from the real commercial thin-film solar panel was demonstrated. • A novel and low-cost physical separation process was induced to peer off the solar panel layer by layer via the extremely low-temperature liquid nitrogen treatment. • An extraction and stripping process was designed to separate Cu, In, and Ga from a complicated multi-element system individually. • Highly pure valuable metal oxides were recovered as the final products, establishing a possible curcular economy model for waste solar panel recycling and recovery. [ABSTRACT FROM AUTHOR]

Abstract: Template-free, one step formation of Cu(In, Ga)Se2 (CIGS) nanotip arrays (NTRs) to enhance device efficiency were discussed. Through Ar+ ion milling process, the CIGS NTRs could be formed directly on the CIGS layer. The angles and lengths of CIGS NTRs could be precisely controlled by incident angle of Ar+ beam and milling time, respectively. Mechanisms were proposed to be a self-masking effect by Cu segregation formed at early stage confirmed by Transmission Electron Microscopy, Grazing Incidence X-ray Diffraction, Energy Dispersive Spectroscopy, and Auger Electron Spectroscopy. Measurements of devices on various KCN washing time and thickness of CdS buffer layer were reported to achieve the highest efficiency of CIGS NTRs devices. This approach provides one-step fast process without templates, easy integration with in-line sputtering process, and no post-selenizatoin process for the formation of CIGS nanostructure, which can stimulate great attention not only in academic investigations but also in industrial side for practical applications. [Copyright &y& Elsevier]

Abstract: The characteristics of the Cu-rich Cu(In,Ga)Se2 (CIGS) films prepared by one-step sputtering process from a single quaternary target have been studied. The influences of working pressure, substrate temperature, Mo back contact, and KCN treatment on the properties of CIGS films were investigated. Target stability has been in-situ monitored by using optical emission spectroscopy. Obvious compositional change due to the KCN effect was observed, while only slight variation was caused by working pressure. We found the preferred orientation and crystallinity of one-step sputtered CIGS films were affected by the working pressure and substrate temperature when CIGS were directly deposited on the glass substrates. However, for the device fabrication, Mo back contacts dominated the growth behavior of CIGS films and induced better crystallinity with larger CIGS grain sizes. To explore the electrical properties of CIGS films on Mo back contacts, we developed a simple two-point probe measurement to examine the conductive channels within CIGS films before the device fabrication. Finally, one-step sputtered CIGS devices showed the efficiency of more than 8% at the working pressure of 0.4–2.7Pa with KCN treatment. [Copyright &y& Elsevier]

Abstract: Many approaches had been reported to successfully reduce the transition temperature of FePt from A1 to L10 phase, though without detailed knowledge. In this work, we deposited the metastable AgPt layer adjacent to the Fe layer and addressed the importance of vacancies in the disorder–order transition of FePt at reduced temperatures on the basis of a kinetic diffusion model. The decomposition of the metastable AgPt phase, creating excess vacancies during the post-deposition annealing process, accelerated the intermixing between Fe and Pt and the nucleation of L10 FePt. The evolution of phase transformation from AgPt–Fe to L10 FePt–Ag was monitored by in situ high temperature X-ray diffractometry and was also validated by first-principles calculations. The intermixing between Fe and Pt and the nucleation of L10 FePt after annealing at 230°C were directly observed by transmission electron microscopy and grazing incidence X-ray diffractometry, respectively. With the assistance of the decomposition of AgPt, we obtained a (001)-dominated L10 FePt film with an out-of-plane coercivity as large as 13.3 kOe after annealing at a temperature as low as 350°C. The principles of the proposed method can be applied for versatile disorder–order phase transitions. [Copyright &y& Elsevier]

Abstract: One-step fabrication of the chalcopyrite Cu(In,Ga)Se2 (CIGS) absorber layer without excess Se supply during/after deposition or post-selenization treatments is reported. By using pulse DC sputtering from a single quaternary CIGS target, the chalcopyrite structure is spontaneously developed on the substrate at 500°C even without extra Se supply. The obtained CIGS absorber layer possesses columnar grains with (112) preferred orientation. Device efficiency of 8.22% is observed for slightly Se-deficient CIGS films. By further tuning the target composition, the efficiency is enhanced to 10.14%. We demonstrate that the device-quality CIGS absorber can be formed even in the Se-deficient environment and further improvement of efficiency can be achieved by tuning the Se content of the target. Accordingly, our one-step sputtering process shows great potential for mass production of thin film CIGS solar cells with a low cost and a high throughput. [Copyright &y& Elsevier]

Abstract: An efficient contrast agent for magnetic resonance imaging (MRI) is essential to enhance the detection and characterization of lesions within the body. In this study, we described the development of biodegradable nanoparticles with a core–shell structure to formulate superparamagnetic iron oxide (CSNP–SPIO) for MRI. The developed nanoparticles were composed of a hydrophobic PLGA core and a positively-charged glycol chitosan shell. The results obtained by transmission electron microscopy, energy dispersive X-ray analysis, electron energy loss spectroscopy, and X-ray diffraction measurement confirmed that the prepared nanoparticles had a core–shell structure with SPIO in their core area. No aggregation of nanoparticles was observed during storage in water, as a result of the electrostatic repulsion between the positively-charged nanoparticles. The magnetic properties of nanoparticles were examined by a vibrating sample magnetometer and a superconducting quantum interference device; the results showed that the superparamagnetism of SPIO was preserved after the CSNP–SPIO formulation. In tracking their cellular internalization pathway, we found that CSNP–SPIO accumulated in lysosomes. In the biodistribution study, a high level of radioactivity was observed in the liver shortly after administration of the 99mTc-labeled CSNP–SPIO intravenously. Once taken up by the liver cells, the liver turned dark on T 2* images. Following cellular internalization, CSNP–SPIO were broken down gradually; therefore, with time increasing, a significant decrease in the darkness of the liver on T 2* images was found. The aforementioned results indicate that the developed CSNP–SPIO can serve as an efficient MRI contrast agent and could be degraded after serving their imaging function. [Copyright &y& Elsevier]