Flexible Cu(In,Ga)Se2 solar cells with reduced absorber thickness

Reduction of the absorber thickness combined with deposition on a flexible substrate is a technically viable strategy to allow lower cost manufacturing of Cu(In,Ga)Se₂ solar modules. Flexible plastic substrates, however, require a low‐temperature deposition process and appropriate control of the band gap grading for achieving high efficiencies. In this work, we developed solar cells on polyimide films using evaporated Cu(In,Ga)Se₂ absorbers with thickness of 0.8–1.3 µm. The double Ga‐grading profile across the absorber thickness was modified by varying the maximum Cu excess at the end of the second stage or by adapting the In and Ga evaporation flux profiles during the growth process. By minimizing the Cu excess during the intermediate stage of the growth process, no loss in open circuit voltage and fill factor is observed compared with a device having a thicker absorber. Efficiency of 16.3% was achieved for cells with an absorber thickness of 1.25 µm. Insufficient absorption of photons in the long wavelength region is mainly responsible for current loss. By changing the In and Ga evaporation profiles, the shape and position of the Ga notch were effectively modified, but it did not lead to a higher device performance. Modifications of the Ga compositional profile could not help to significantly reduce absorption losses or increase charge carrier collection in absorbers with thickness below 1 µm. Changes of open circuit voltage and fill factor are mostly related to differences in the net acceptor density or the reverse saturation current rather than changes of the double Ga grading. Copyright © 2013 John Wiley & Sons, Ltd.     

Assessment of falsework performance using fuzzy set concepts

Human-based uncertainties which are abundant in falsework construction are seldom included in the assessment of falsework performance. The classical probability concept is impractical and fails to treat the uncertainties which are commonly expressed in linguistic variables. A method of assessing falsework adequacy has been developed based on a fuzzy set concept. This concept interpretes in mathematical terms the linguistic variables of subjective appraisals of the falsework enabling and triggering events and their consequences. Graphical display were constructed from the final assessment and presented as a guide to determine the overall falsework performance. This method can be used as a tool for quality control processes in which reduction of the enabling and triggering events can be conducted to achieve a desired level of overall falsework performance.     

Highly efficient Cu(In,Ga)Se2 solar cells grown on flexible polymer films

Solar cells based on polycrystalline Cu(In,Ga)Se(2) absorber layers have yielded the highest conversion efficiency among all thin-film technologies, and the use of flexible polymer films as substrates offers several advantages in lowering manufacturing costs. However, given that conversion efficiency is crucial for cost-competitiveness, it is necessary to develop devices on flexible substrates that perform as well as those obtained on rigid substrates. Such comparable performance has not previously been achieved, primarily because polymer films require much lower substrate temperatures during absorber deposition, generally resulting in much lower efficiencies. Here we identify a strong composition gradient in the absorber layer as the main reason for inferior performance and show that, by adjusting it appropriately, very high efficiencies can be obtained. This implies that future manufacturing of highly efficient flexible solar cells could lower the cost of solar electricity and thus become a significant branch of the photovoltaic industry.     

核-壳结构有机硅弹性体技术对环氧树脂体系性能的影响

介绍了在双组分环氧树脂体系中采用的核-壳结构有机硅弹性体技术,以及其对涂层机械性能的影响。结果表明,通过采用该技术能明显改善涂层的性能,涂层的抗冲击强度、耐候性、附着力和耐腐蚀性显著提高,滑动阻力明显降低。     

Magnetic properties of terrestrial moss (Hylocomium splendens) along a north-south profile crossing the city of Oslo, Norway

Magnetic measurements are routinely used in geophysics and environmental sciences to obtain detailed information about concentrations and quality of iron minerals. Here, magnetic properties of 38 terrestrial moss samples (Hylocomium splendens) from a ~ 120 km south-north transect through Oslo are studied to gain better insight into the nature and origin of their Fe fraction. The concentration-dependent quantities, magnetic susceptibility k, and isothermal remanent magnetization IRM(700mT) after weight normalization have significantly higher values in urban regions, and parallel the previously found concentration signals of 16 out of 29 chemical elements (Ag, Al, Au, Bi, Cd, Co, Cr, Cu, Fe, Mo, Ni, Pb, Pt, Sb, Ti, and Zn). Because there is no evidence that Hylocomium splendens produces biogenic magnetic remanence carriers, the increase in IRM is attributed to adsorption of dust containing iron oxide minerals. This agrees with previous observations that Ti concentrations, related to local mineral dust, have a peak in Oslo, and at sites close to known dust sources. Scanning electron microscopy images also showed an increased density of minerogenic particles on the moss surfaces in the urban samples, which qualitatively supports the dust based interpretation. The concentration-independent ratios k/Fe and IRM(700mT)/Fe also have extreme values in the urban parts of the transect. This indicates that more of the total iron occurs in magnetically ordered form and in remanence carriers, interpreted as adsorbed dust. In addition, purely magnetic ratios displayed differences in urban and rural areas, indicating that their magnetic dust particles are inherently of different types. Therefore, it is likely that anthropogenic dust sources contribute considerably to the magnetic signal. Urban dust enhancement is not exclusively due to increased erosion, leading to higher loads of geogenic dust in the atmosphere, but also to specific anthropogenic sources from combustion, corrosion, or other synthetic emitters.     

Novel anti-reflection technology for GaAs single-junction solar cells using surface patterning and Au nanoparticles

Single-junction GaAs solar cell structures were grown by low-pressure MOCVD on GaAs (100) substrates. Micro-rod arrays with diameters of 2 microm, 5 microm, and 10 microm were fabricated on the surfaces of the GaAs solar cells via photolithography and wet chemical etching. The patterned surfaces were coated with Au nanoparticles using an Au colloidal solution. Characteristics of the GaAs solar cells with and without the micro-rod arrays and Au nanoparticles were investigated. The short-circuit current density of the GaAs solar cell with 2 microm rod arrays and Au nanoparticles increased up to 34.9% compared to that of the reference cell without micro-rod arrays and Au nanoparticles. The conversion efficiency of the GaAs solar cell that was coated with Au nanoparticles on the patterned surface with micro-rod arrays can be improved from 14.1% to 19.9% under 1 sun AM 1.5G illumination. These results show that micro-rod arrays and Au nanoparticle coating can be applied together in surface patterning to achieve a novel cost-effective anti-reflection technology.     

3D Environment Is Required In Vitro to Demonstrate Altered Bone Metabolism Characteristic for Type 2 Diabetics

A large British study, with almost 3000 patients, identified diabetes as main risk factor for delayed and nonunion fracture healing, the treatment of which causes large costs for the health system. In the past years, much progress has been made to treat common complications in diabetics. However, there is still a lack of advanced strategies to treat diabetic bone diseases. To develop such therapeutic strategies, mechanisms leading to massive bone alterations in diabetics have to be well understood. We herein describe an in vitro model displaying bone metabolism frequently observed in diabetics. The model is based on osteoblastic SaOS-2 cells, which in direct coculture, stimulate THP-1 cells to form osteoclasts. While in conventional 2D cocultures formation of mineralized matrix is decreased under pre-/diabetic conditions, formation of mineralized matrix is increased in 3D cocultures. Furthermore, we demonstrate a matrix stability of the 3D carrier that is decreased under pre-/diabetic conditions, resembling the in vivo situation in type 2 diabetics. In summary, our results show that a 3D environment is required in this in vitro model to mimic alterations in bone metabolism characteristic for pre-/diabetes. The ability to measure both osteoblast and osteoclast function, and their effect on mineralization and stability of the 3D carrier offers the possibility to use this model also for other purposes, e.g., drug screenings.