Ground-based lidar measurements from Ny-Ålesund during ASTAR 2007

During the Arctic Study of Tropospheric Aerosol, Clouds and Radiation (ASTAR) in March and April 2007, measurements obtained at the AWIPEV Arctic Research Base in Ny-Ålesund, Spitsbergen at 78.9° N, 11.9° E (operated by the Alfred Wegener Institute for Polar and Marine Research – AWI and the Institut polaire français Paul-Emile Victor – IPEV), supported the airborne campaign. This included lidar data from the Koldewey Aerosol Raman Lidar (KARL) and the Micro Pulse Lidar (MPL), located in the atmospheric observatory as well as photometer data and the daily launched radiosonde. The MPL features nearly continuous measurements; the KARL was switched on whenever weather conditions allowed observations (145 h in 61 days). From 1 March to 30 April, 71 meteorological balloon soundings were performed and compared with the concurrent MPL measurements; photometer measurements are available from 18 March. For the KARL data, a statistical overview of particle detection based on their optical properties backscatter ratio and volume depolarization can be given. The altitudes of the occurrence of the named features (subvisible and visible ice and water as well as mixed-phase clouds, aerosol layers) as well as their dependence on different air mass origins are analyzed. Although the spring 2007 was characterized by rather clean conditions, diverse case studies of cloud and aerosol occurrence during March and April 2007 are presented in more detail, including temporal development and main optical properties as depolarization, backscatter and extinction coefficients. Links between air mass origins and optical properties can be presumed but need further evidence

Springtime Arctic aerosol: Smoke versus Haze, a case study for March 2008

During March 2008 photometer observations of Arctic aerosol were performed both at a Russian ice-floe drifting station (NP-35) at the central Arctic ocean (56.7e42.0 E, 85.5e84.2 N) and at Ny-Ålesund, Spitsbergen (78.9 N, 11.9 E). Next to a persistent increase of AOD over NP-35, two pronounced aerosol events have been recorded there, one originating from early season forest fires close to the city of Khabarovsk (“Arctic Smoke”), the other one showed trajectories from central Russia and resembled more the classical Arctic Haze. The latter event has also been recorded two days later over Ny-Ålesund, both in photometer and lidar. From these remote sensing instruments volume distribution functions are derived and discussed. Only subtle differences between the smoke and the haze event have been found in terms of particle microphysics. Different trajectory analysis, driven by NCEP and ECMWF have been performed and compared. For the data set presented here the meteorological field, due to sparseness of data in the central Arctic, mainly limits the precision of the air trajectories

Gallium gradients in Cu In,Ga Se2 thin film solar cells

The gallium gradient in Cu(In,Ga)Se2 (CIGS) layers, which forms during the two industrially relevant deposition routes, the sequential and co-evaporation processes, plays a key role in the device performance of CIGS thin-film modules. In this contribution, we present a comprehensive study on the formation, nature, and consequences of gallium gradients in CIGS solar cells. The formation of gallium gradients is analyzed in real time during a rapid selenization process by in situ X-ray measurements. In addition, the gallium grading of a CIGS layer grown with an in-line coevaporation process is analyzed by means of depth profiling with mass spectrometry. This gallium gradient of a real solar cell served as input data for device simulations. Depth-dependent occurrence of lateral inhomogeneities on the μm scale in CIGS deposited by the co-evaporation process was investigated by highly spatially resolved luminescence measurements on etched CIGS samples, which revealed a dependence of the optical bandgap, the quasi-Fermi level splitting, transition levels, and the vertical gallium gradient. Transmission electron microscopy analyses of CIGS cross-sections point to a difference in gallium content in the near surface region of neighboring grains. Migration barriers for a copper-vacancy-mediated indium and gallium diffusion in CuInSe2 and CuGaSe2 were calculated using density functional theory. The migration barrier for the InCu antisite in CuGaSe2 is significantly lower compared with the GaCu antisite in CuInSe2, which is in accordance with the experimentally observed Ga gradients in CIGS layers grown by co-evaporation and selenization processes

Chemical Gradients in Cu(In,Ga)(S,Se)2 Thin-Film Solar Cells: Results of the GRACIS Project

The German joint research project “Chemical Gradients in Cu(In,Ga)(S,Se)2” (GRACIS) is an initiative to gain a better physical understanding concerning the formation of chemical gradients in the Cu(In,Ga)(S,Se)2 (CIGS) absorber layers and at the CIGS/buffer interface. This article presents the current status of the GRACIS project after three years of execution with results concerning phase formation during chalcogenization and coevaporation processes, influence of Ga grading on structural and electrical parameters as well as on inhomogeneities on the μm scale of CIGS. Special features of the CIGS/Zn(O,S) buffer interface are discussed and compared to CIGS solar cells with CdS buffer. In addition, our experimental results are supported by 3D simulations and calculations using screened-exchanged hybrid density functional theory