Evolution of Structural and Optical Properties on PIN and NIP pm-Si:H Devices During 400 Hrs of Light-Soaking

ABSTRACTPm-Si:H PIN and NIP solar cells structures grown using plasma enhanced chemical vapor deposition (PECVD) technique were analyzed during 400 hrs of light-soaking exposition. The evolution of the structural and optical properties was observed and characterized by Raman spectroscopy, spectroscopic ellipsometry. The effect observed is related to defects creation due to induced hydrogen diffusion, break of Si-H bonds and the generation of dangling bonds that causes less passivated films. The film microstructure, and therefore the optical properties varied with the exposition time. The crystalline fraction of these structures presents a slight decrease and it is observed to be between 15 to 24% for the PIN and 5 to 10% for the NIP. The optical gap increases from 1.66 to 1.68 eV for the PIN structure while for the NIP no significant change is observed during light-soaking. Hydrogen diffusion during lights soaking generates a decrease on the absorption properties of the films which in turn is expected to reduce the device efficiency during operation. In this work we show that long range motion of hydrogen during light-soaking causes a hydrogen rearrangement on the film and microstructure changes. We determined that there is not an pronounced change on the film structure during prolonged light exposition related to the stability of the pm-Si:H films. The PIN structure properties are more affected during light soaking in comparison to the NIP structure which is expected to cause less degradation of its optoelectronic properties under illumination, and a more stable device during operation.

Negative Ion Electrospray Ionization Mass Spectrometry and Computational Studies on Substituted 7-Hydroxycoumarins

Twenty-two substituted 7-hydroxycoumarins were studied by negative ion electrospray ionization collision-induced dissociation (CID) mass spectrometry. Fragmentation pathways were also investigated by computation method using the B3LYP density functional theory. In general, the most important fragmentations of the 7-hydroxycoumarin [M – H]− ions were the elimination of CO2 and CO which agreed with the calculated energies of the proposed fragmentation reactions. In most cases, methyl group elimination was also favorable. Methyl group elimination occurred in three different ways, the most interesting being hydrogen rearrangement from a neighboring alkyl group to a ring carbon, which led to a benzyl radical formation. In some cases, CH2CO elimination was observed as well. Isomeric compounds gave rise to different CID spectra.

Gas Chromatography Electron Ionization Mass Spectrometric Analysis of O-Alkyl Methylphosphinates for Verification of Chemical Weapons Convention

We describe the gas chromatography/mass spectrometric (GC/MS) analysis of O-alkyl methylphosphinates (AMPs), which are included in Schedule 2B4 chemicals in the Chemical Weapons Convention (CWC). GC/MS analysis of a variety of AMPs and their deuterated analogs revealed that their fragmentations were determined by α-cleavages, McLafferty +1 and hydrogen rearrangement. Based on the obtained electron ionization mass spectra of AMPs, the fragmentation routes were rationalized, which were substantiated by the GC/MS analysis of deuterated analogs.