Title :
Quality characterization of silicon bricks using photoluminescence imaging and photoconductive decay
Author :
Johnston, Steve ; Yan, Fei ; Zaunbrecher, Katherine ; Al-Jassim, Mowafak ; Sidelkheir, Omar ; Ounadjela, Kamel
Author_Institution :
Nat. Renewable Energy Lab., Golden, CO, USA
Abstract :
Imaging techniques can be applied to multicrystalline silicon solar cells throughout the production process, which includes as early as when the bricks are cut from the cast ingot. Photoluminescence (PL) imaging of the band-to-band radiative recombination is used to characterize silicon quality and defects regions within the brick. PL images of the brick surfaces are compared to minority-carrier lifetimes measured by resonant-coupled photoconductive decay (RCPCD). RCPCD is a transient photoconductive decay technique that monitors the recombination of excess carriers using a frequency of about 420 MHz. Carriers are excited by nanosecond laser pulses of long-wavelength light in the range of 1150 nm. The low frequency and long penetration depth of light promote measurement of carriers away from the surface such that lifetimes of up to 100 μs are measured in upgraded-metallurgical-grade silicon, and up to 200 μs in electronic-grade silicon bricks. PL intensity shows correlation to lifetime in addition to the valuable spatial information from top to bottom of the brick and defect regions throughout the brick.
Keywords :
brick; elemental semiconductors; high-speed optical techniques; laser beam effects; metallurgical industries; minority carriers; photoconductivity; photoluminescence; quality assurance; silicon; Si; band-to-band radiative recombination; cast ingot; defects; light long-penetration depth; light low-frequency depth; long-wavelength light; minority-carrier lifetimes; multicrystalline silicon solar cells; nanosecond laser pulse; photoluminescence imaging; resonant-coupled photoconductive decay; silicon quality characterization; spatial information; time 100 mus; transient photoconductive decay technique; upgraded-metallurgical-grade silicon bricks; wavelength 1150 nm; Charge carrier lifetime; Correlation; Frequency measurement; Imaging; Photoluminescence; Silicon; Wavelength measurement; charge-carrier lifetime; imaging; impurities; infrared imaging; photoconductivity; photoluminescence; photovoltaic cells; silicon;
Conference_Titel :
Photovoltaic Specialists Conference (PVSC), 2012 38th IEEE
Conference_Location :
Austin, TX
Print_ISBN :
978-1-4673-0064-3
DOI :
10.1109/PVSC.2012.6317645