Optical absorption coefficient and minority carrier diffusion length measurements in low-cost silicon solar cell material

Abstract

The optical absorption coefficient of silicon solar cell material grown by three low-cost growth methods was measured in the wavelength interval 0.8≤λ≤1.0 μm, the wavelength region of interest in surface photovoltage measurements of the minority carrier diffusion length. The square root of the absorption coefficient was found to vary linearly with photon energy over the wavelengths studied, and the measured data agree with a linear empirical fit to within 0.5% RMS. The absorption coefficients obtained are slightly lower than those reported by Runyan, with the greatest disagreement at long wavelengths. Minority carrier diffusion lengths computed using the present absorption coefficients are approximately 16% greater than those calculated using Runyan’s data. Excellent sample-to-sample agreement within and between lots indicates that for two of the growth methods studied, material quality as judged by optical properties has not been sacrificed by the use of low-cost growth methods. Samples grown by the third growth method studied showed measurably poorer optical quality.

The silicon on dust substrate path to make solar cells directly from a gaseous feedstock

“…The minority carrier diffusion length can be extracted by plotting the inverse internal quantum efficiency (IQE) versus the absorption length and computing the intercept at the horizontal axis [11], yielding a diffusion length of around 70 μm. We used optical absorption data from [12].…”

Minority Carrier Diffusion Lengths in Multi-Crystalline Silicon Wafers and Solar Cells

“…These authors used the a(l) data of ref. 6 (eq.1), relevant to crystalline, stress relieved Si, these data have been critically reviewed by several authors [8,9]. In fig.…”