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Space charge dynamics in a low-density polyethylene (LDPE) film is calculated using mobility based on the Gaussian disorder model (GDM), which is commonly used to describe hopping conduction in disordered materials. The GDM exhibits a negative differential mobility under a strong positional disorder. In simulations, injected charges do not form packet-like space charges when using a constant mobility model, whereas packet-like space charges appear when using the mobility based on the GDM. The simulation using the GDM mobility can reproduce the time and voltage dependences of space charge behavior in LDPE. The calculated space charge, electric field, and current density profiles show good agreement with experimental results. [ABSTRACT FROM AUTHOR]

Pulsed electroacoustic (PEA) space charge measurement of low‐density polyethylene using a spin‐coated poly(vinylidene fluoride‐trifluoroethylene) thin film is demonstrated. The space charge profile of a low‐density polyethylene film with a thickness of 150 μm is measured by PEA method. Compared with conventional 9 and 30‐μm piezoelectric films, the space charge profile obtained by the 3‐μm spin‐coated film shows better spatial resolution. Furthermore, acoustic attenuation of a PEA signal is also analytically studied using the Kelvin‐Voigt model for viscoelastic materials. [ABSTRACT FROM AUTHOR]

Cu2ZnSnS4 (CZTS) thin-film solar cells are considered promising for terawatt-scale production. It has been established that in the fabrication process of CZTS thin-film solar cells, a water-rinse treatment for the CZTS surface yields a great improvement in conversion efficiency. We studied the mechanism of the water-rinse treatment on an aged crystalline-CZTS sample, using the X-ray absorption near-edge structure (XANES) technique, which is highly sensitive for oxidation states of sulfur. The sulfur K-edge XANES spectra revealed a dramatic change at around 2480 eV after a 3-min water-rinse treatment. By comparison with the spectra of reference samples, we posit the removal of surface sulfate cations as a possible source for this behavior. From further comparison with the spectrum of a thin-film sample, we discuss the use of this short 3-min treatment time in actual device-fabrication procedures. (© 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [ABSTRACT FROM AUTHOR]

By the compound-source molecular beam epitaxy (CS-MBE), GaN:Eu and AlGaN films grown on both Al2O3(0001) and GaAs(100) substrates were prepared. Under RHEED observation, streak RHEED patterns from GaN were observed. This result shows that the surface of the film grown by CS-MBE is atomically flat. From the XRD measurements, for GaN:Eu/Al2O3(0001), the film was oriented to c-axis. On the other hands, for GaN:Eu/GaAs(100), the layer includes both the hexagonal and cubic phases. From the PL measurements, the PL spectra of both GaN:Eu/Al2O3 and GaN:Eu/GaAs(100) showed PL peaks related to Eu3+ ion. For GaN:Eu/GaAs(100), it is possible that part of Eu atom incorporates cubic-GaN site (© 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [ABSTRACT FROM AUTHOR]

Room-temperature photoluminescence (PL) has been studied in Cu(In,Ga)Se2 (CIGS) films with emphasis on the near-band-edge PL of CIGS during the solar cell fabrication process. A step-by-step PL spectrum mapping measurement was carried out on the following cell processes: depositions of CIGS absorber, CdS buffer, high-resistivity undoped ZnO buffer, and low-resistivity Al-doped window ZnO layers, and the final cell separation process by mechanical scribing. The systematic change in PL intensity during the process has been studied, and the usefulness of PL as a noncontact process monitor has been demonstrated. [ABSTRACT FROM AUTHOR]