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Solar Cells Thin Film Technologies Part 7

Tham khảo tài liệu 'solar cells thin film technologies part 7', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Architectural Design Criteria for Spacecraft Solar Arrays 169 solids which are of interest to the solar array designer are ionisation and atomic displacement. Ionisation occurs when orbital electrons are removed from an atom or molecule in gases liquids or solids. The measure of the intensity of ionising radiation is the roentgen. The measure of the absorbed dose in any material of interest is usually defined in terms of absorbed energy per unit mass. The accepted unit of absorbed dose is the rad 100 erg g or 0.01 J kg . For electrons the absorbed dose may be computed from the incident fluence o in cm-2 as Dose rad 1.6x10-8 dE dx o where dE dx in MeV cm2 g-1 is the electron stopping power in the material of interest. In this manner the effects of an exposure to fluxes of trapped electrons of various energies in space can be reduced to an absorbed dose. By the concept of absorbed dose various radiation exposures can be reduced to absorbed dose units which reflect the degree of ionisation damage in the material of interest. This concept can be applied to electron gamma and X-ray radiation of all energies. Several ionisation related effects may degrade the solar cell assemblies. The reduction of transmittance in solar cell cover glasses is an important effect of ionising radiation. The basis for solar cells damage is the displacement of semiconductor atoms from their lattice sites by fast particles in the crystalline absorber. The displaced atoms and their associated vacancies after various processes form stable defects producing changes in the equilibrium of carrier concentrations and in the minority carrier lifetime. Such displacements require a certain minimum energy similar to that of other atomic movements. Seitz and Koehler 1956 estimated the displacement energy is roughly four times the sublimation energy. Electron threshold energies up to 145 keV have been reported. Particles below this threshold energy cannot produce displacement damage therefore the space .