We present results of computer simulations of the light induced degradation of amorphous silicon solar cells. It is now well established that when amorphous silicon is illuminated the density of dangling bond states increases. Dangling bond states produce amphoteric electronic mid-gap states which act as efficient charge trapping and recombination centres. The increase in dangling bond states causes a decrease in the performance of amorphous silicon solar cells. To show this effect, a modelling approach has been developed which uses the density of localised states with exponentially increasing band-tails and dangling bond defect states distribution chosen according to the defect pool model. The calculation of the evolution of dangling bond state density during illumination has been achieved through a dynamic scaling relation derived from a defect creation model. The approach considers the amphoteric nature of the dangling bond state and thus accounts for the contributions of the different charge states of the dangling bond during the degradation process. This paper attempts to describe the simulation approach which calculates the defect density as a function of energy, position in the solar cell and illumination time. In excellent agreement with other workers; our simulation results show that the increase in the density of neutral dangling bond states during illumination is higher than of the charged states. (C) 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.@en

Light soaking experiments have been conducted on a-Si:H p-i-n solar cells with a silicon carbide buffer layer at the p/i interface. The rate of light induced degradation in the performance of these solar cells is higher in the initial stages of light soaking and assumes the same levels as the cells without a buffer layer with prolonged light soaking. Computer modelling has revealed that a graded band gap buffer layer at the p/i interface containing a slightly acceptor doped defective layer next to the p-layer improves the initial performance of a-Si:H p-i-n solar cells. The modelling also reveals that the effect of the buffer layer on solar cell performance depends critically on the configuration and composition of the buffer layer. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)@en

The epitaxial growth of nickel-copper surface alloys on a copper substrate is studied by high energy ion scattering. Nickel has been deposited by decomposition of nickel carbonyl on the (100) surface of copper at an elevated temperature. The composition of the grown overlayers is measured by glancing angle Rutherford backscattering spectroscopy. The morphology is investigated by ion channeling. The samples are studied after exposure as well as after subsequent annealing. In addition, LEED and AES are used as complementary techniques. It is found that an overlayer with a thickness of about ten monolayers is a surface alloy: it contains about equal amounts of well mixed nickel and copper. The strain in this surface alloy is equal to the strain expected for pseudomorphic layer growth. A much thicker overlayer contains only a few percent copper and has grown epitaxially; however, there are many defects present at the interface. The strain in this surface alloy exceeds the equilibrium strain, but this excess disappears by annealing. The thick surface alloy is broken apart into separate regions, which causes rapid interdiffusion during annealing.@en