Photoelectron spectromicroscopy at chalcopyrite films

CuInSe2 films were prepared by MBE on GaAs 111 A substrates. ZnSe and ZnO are subsequently deposited in situ by MOMBE. Interface parameters like band offsets and morphology are studied by X ray photoelectron spectroscopy XPS and Low energy electron diffraction LEED . Spectroscopic XPEEM X ray Photo electron emission microscopy at the U49 2 PGM2 beamline at BESSY was used to investigate the lateral homogenity of the interface. After annealing in situ a lateral inhomogenious In diffusion is observed into the ZnSe ZnO interfac

Origin of Interface Limitation in Zn O,S CuInS2 Based Solar Cells

Copper indium disulfide CuInS2 grown under Cu rich conditions exhibits high optical quality but suffers predominantly from charge carrier interface recombination, resulting in poor solar cell performance. An unfavorable cliff like conduction band alignment at the buffer CuInS2 interface could be a possible cause of enhanced interface recombination in the device. In this work, we exploit direct and inverse photoelectron spectroscopy together with electrical characterization to investigate the cause of interface recombination in chemical bath deposited Zn O,S co evaporated CuInS2 based devices. Temperature dependent current voltage analyses indeed reveal an activation energy of the dominant charge carrier recombination path, considerably smaller than the absorber bulk band gap, confirming the dominant recombination channel to be present at the Zn O,S CuInS2 interface. However, photoelectron spectroscopy measurements indicate a small 0.1 eV spike like conduction band offset at the Zn O,S CuInS2 interface, excluding an unfavorable energy level alignment to be the prominent cause for strong interface recombination. The observed band bending upon interface formation also suggests Fermi level pinning not to be the main reason, leaving near interface defects as recently observed in Cu rich CuInSe2 as the likely reason for the performance limiting interface recombinatio

Lateral Distribution of Anodic Oxides and Strain on Self Organized Fractal Silicon Photoelectrodes

Fractal microtopographies were prepared on n type Si 100 photoelectrodes by self organized anodic dissolution in concentrated ammonium fluoride. The concurrent formation of etch structures, extending along preferential crystallographic directions, and inhomogeneous anodic oxide layers was investigated by synchrotron radiation photoelectron spectroscopy SRPES and electrochemicalanalysis. It is shown that two types of SiO2 layers are forming at the surface, distinguishable by the layer thickness and a shift in the Si 4 binding energy. The finding is based on chemical analysis with spatial resolution using Photoelectron Emission Microscopy PEEM at the tip of fractal branches, reversed contrasts were obtained by detection of the PEEM photoelectron yield of the respective SiO2 layers. Electrochemical analysis was applied for the first time to assess the etching behavior of inhomogeneously distributed oxides in real time. Oxide thicknesses of about 3 4 nm within microstructures and 5 8 nm on planar areas could bederived. The observation of locally attenuated PEEM signals at the structure boundaries after oxide removal is tentatively assigned to residual strain in a surface near region. This interpretation thereby complements a recently developed theoretical model for the physicochemical evolution of fractal microstructures on silicon. 2012 The Electrochemical Society. [DOI 10.1149 2.030206jes] All rights reserve

Microscopic investigation of the CdS buffer layer growth on Cu In,Ga Se2 absorbers

To obtain highly efficient thin film solar cell devices, a thin buffer layer of CdS is deposited onto a Cu In,Ga Se2 absorber layer. Here, the authors report a photoemission electron microscopy study investigating the growth of evaporated CdS buffer layers. For thin CdS layers 1 nm thickness , they observed enhanced CdS growth on some grains, while other grains remain uncovered or only weakly covered. For thicker CdS layers, they observed a more homogeneous growth. After annealing these layers, an increase in the detailed In and Se structure is observed as well as the reappearance of the inhomogeneous Cd distribution. This indicates an intermixing of CdS and Cu In,Ga Se2. The influence of such interdiffusion on solar cell efficiency is discusse