Photoluminescence Characterization of Phosphorus Diffusion and Hydrogenation in Continuous Wave Diode Laser Crystallized
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Photoluminescence Characterization of Phosphorus Diffusion and Hydrogenation in Continuous Wave Diode Laser Crystallized Si Thin-Film on Glass. Miga Jung1, Anthony Teal1, Rhett Evans2, Jae Sung Yun1, Sergey Varlamov1, Martin A. Green1 1 University of New South Wales, Kensington, NSW, 2052, Australia. 2 Suntech R&D Australia Pty Ltd, 5 Parkview Drive, Homebush Bay, NSW, 2127 Australia. ABSTRACT In this paper, the effect of phosphorus diffusion and hydrogen passivation on the material properties of laser crystallised silicon on glass is investigated. Photoluminescence imaging, as well as Hall effect and Suns-Voc techniques are applied for the characterisation of laser crystallized silicon thin-film material properties. Hall effect as well as Suns-Voc measurements supports the photoluminescence imaging results; phosphorus diffusion and hydrogen passivation of laser crystallized films improves the overall material quality. Hydrogen passivation is more effective at improving the electronic properties of the laser crystallized films than phosphorus diffusion. Hydrogen passivated samples improved the photoluminescence intensity even further by a factor of 3. In addition, a correlation between photoluminescence intensity and open-circuit voltage is demonstrated: samples with highest photoluminescence intensity (1678 counts/s), gave the highest voltage (530 mV). Hall effect measurement shows a significant improvement in the bulk material, with carrier mobility increasing from 208 cm2/Vs to 488 cm2/Vs. INTRODUCTION Liquid phase crystallization of silicon thin-film on glass (LPSCG) using a continuous wave diode laser has allowed the fabrication of high quality silicon thin-film on glass, with solar cell voltages surpassing the voltages previously achieved on poly-silicon based thinfilm cells grown on foreign substrates [1]. However, LPCSG is a spatially inhomogeneous material that can often vary in the material parameters of defect density, crystal orientation and grain size. This variation can also be observed within a single sample [1]. For the improvement of efficiency, it is essential to characterise the effects of solar cell processing on the material properties. The most well-known and acknowledged passivation techniques for improving minority carrier lifetimes in silicon-based films are phosphorus gettering and hydrogen passivation [2, 3]. In this paper, the effect of phosphorus diffusion and hydrogen passivation on the electronic properties of LPCSG is investigated through photoluminescence imaging (PL), Hall Effect and Suns-Voc. In addition, we investigate the relationship between PL imaging and open-circuit voltage (Voc) of LPCSG films. Theory – PL intensity and Voc
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Relating PL intensity to the Voc of a solar cell is a convenient way of evaluating cell performance and the influence of processes on the material. The relationship between PL intensity and the carrier concentration is shown in equation (1); where Ai is a calibration factor determined by experiment, B is the radiative recombination coefficient, ND is
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