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8th World Conference on Photovoltaic Energy Conversion; 670-673, The science and engineering of soiling of solar devices is now well into its eighth decade, with more than 400 research papers this past year. The interests are technologically diverse, ranging from performance monitoring to mitigation methodologies. The derating of the energy output from a PV installation is a concern for both technology reliability and operating costs. This paper examines aspects of the relationships between the soiling of PV modules and the effects of this environmental process on the resulting performance and temperature characteristics. Thin-film CdTe and crystalline-Si modules are evaluated and compared for both uniform and non-uniform soiling patterns. The comprehensive studies document and compare laboratory simulations with actual outdoor cases for framed and frameless module structures. There is some emphasis on edge-buildup patterns, which are among the most common non-uniform deposition configurations, for both portrait and landscape module orientations. These non-uniform accumulations not only cause decrease in the produced power- output but result in shading that can cause increased confine areal heating (“hot spots”) that can lead to module degradation. This paper further documents effects of both uniform and non-uniform soiling patterns on the J-V characteristics, documenting changes in the shape of these characteristics with the geometry and thickness distributions on the module surfaces. The special focus is to evaluate the specific effects of the non-uniform distribution on module temperature distributions using IR thermography and complementary techniques. These soiling patterns, performance parameters, and temperature distributions/levels are determined for modules in several Brazil climate zones. Temperature differences can exceed 40°C in excess normal operating temperatures for cells due to non-uniform soiling for the crystalline-Si cases; and corner soiling can lead to hot-spot formation no matter the module orientation.

This paper addresses the effects of a short high-temperature step, corresponding to the firing of the metallization on Si solar cells, on the structural and optical properties of high-rate (> 0.5 nm/s) plasma deposited a-SiNx:H films. Three different types of a-SiNx:H films were prepared using (i) a N2-SiH4 expanding thermal plasma, (ii) a NH3-SiH4 expanding thermal plasma, and (iii) a NH3-SiH4 microwave plasma. The changes in structural and optical properties of the films have been investigated before and after the high temperature step by means of elastic recoil detection, spectroscopic ellipsometry, and Fourier transform infrared spectroscopy. The high temperature step induces significant changes in hydrogen content, mass density, and optical properties of the films and these thermally induced effects are more enhanced for Si-rich films than for N-rich films. It is found that a high density and thermal stability of the as-deposited films are crucial for obtaining good bulk passivation properties.

Excellent and thermally stable surface passivation of SiNx:H grown using N2 and SiH4 as precursor gases has been obtained with MicroWave PECVD. The thermal stability of the surface passivation is even better than that for layers deposited with NH3 and SiH 4. Additionally, we found that the bulk passivating properties of SiNx:H deposited with N2+SiH4 are as good as that of the standard SiNx:H deposited with NH3+SiH 4. Absorption at shorter wavelengths in SiNx:H layers deposited with N2+SiH4 is somewhat higher. Solar cell efficiencies are comparable for both nitrides.