IMPACT OF IRON CONTAMINATION IN MULTICRYSTALLINE SILICON SOLAR CELLS: ORIGINS,CHEMICAL STATES, AND DEVICE IMPACTS

摘要

Synchrotron-based microprobe techniques have been applied to study the distribution, size, chemicalstate, and recombination activity of Fe clusters in two types of mc-Si materials: block cast mc-Si, and AstroPowerSilicon Film? sheet material. In sheet material, high concentrations of metals were found at recombination-active,micron-sized intragranular clusters consisting of micron and sub-micron sized particles. In addition, Fe nanoparticleswere located in densities of ～2×10 7 cm-2 along recombination-active grain boundaries. In cast mc-Si, two types ofparticles were identified at grain boundaries: (1) micron-sized oxidized Fe particles accompanied by other metals(Cr, Mn, Ca, Ti), and (2) a higher number of sub-micron FeSi2 precipitates that exhibited a preferred orientationalong the crystal growth direction. In both materials, it is believed that the larger Fe clusters are inclusions of foreignparticles, from which Fe dissolves in the melt to form the smaller FeSi2 nanoprecipitates, which by virtue of theirmore homogeneous distribution are deemed more dangerous to solar cell device performance. Based on thisunderstanding, strategies proposed to reduce the impact of Fe on mc-Si electrical properties include gettering,passivation, and limiting the dissolution of foreign Fe-rich particles in the melt.