薄膜硅/晶体硅异质结电池中本征硅薄膜钝化层的性质及光发射谱研究

本文采用甚高频等离子体化学气相沉积技术 (VHF-PECVD) 制备薄膜硅/晶体硅异质结电池中的本征硅薄膜钝化层, 光发射谱 (OES) 测量技术研究了硅薄膜沉积过程中等离子体发光谱随时间的变化. 结果表明: 在实验优化条件下等离子体发光谱很快达到稳定 (大约25 s), 并且SiH^*/H_α^* 的比值随时间变化较小, 避免了生长过程中硅薄膜结构的不均匀性, 这主要是SiH₄没有完全耗尽避免了SiH₄的反向扩散. 进一步研究了沉积参数对稳态发光谱和硅薄膜性质的影响, 结果表明: 随着硅烷浓度增加, H_α^*峰强度减小, SiH^*峰强度增加, 薄膜从微晶转变成非晶, 非晶硅薄膜钝化效果好; 随着沉积气压增大, H_α^*和 SiH^*峰强度先增加后减小, 高气压下H_α^*和 SiH^*峰强度下降主要是反应前驱物的聚合形成高聚合物, 不利于形成高质量的硅薄膜, 因此钝化效果下降; 随着反应功率密度增加, H_α^*和 SiH^*峰强度增大, 当功率密度为150 mW/cm² 趋于饱和, 硅薄膜的致密度和钝化效果也开始下降, 50 mW/cm²的低功率密度下硅薄膜钝化效果差可能是由于原子H 浓度低, 不能完全钝化单晶硅表面的悬挂键. 关键词： 薄膜硅 异质结 光发射谱 钝化

Study on the properties and optical emission spectroscopy of the intrinsic silicon thin film in silicon heterojunction solar cells

The intrinsic silicon thin film for passivation of the crystalline silicon wafer surfaces in silicon heterojunction cells was prepared by very high fregucency plasma enhanced CVD (VHF-PECVD). Plasma emission versus time was recorded by optical emission spectroscopy (OES) during the silicon thin film deposition. Results show that the H_α^* and SiH^* signals stabilize soon (about 25 s after deposition) under the optimized deposition conditions, and the variation of SiH^*/H_α^* ratio is little, thus avoiding the structure non-uniformity of silicon film during the growth. The reason is that the SiH₄ back diffusion is avoided owing to SiH₄ being not fully depleted. The study of the influence of the deposition parameters on steady-state plasma emission spectra and properties of silicon films shows that as the SiH₄ concentration increases, the H_α^* decreases and the SiH^* increases, the silicon film will transit from microcrystalline to amorphous, and the good passivation effect can be achieved in the amorphous silicon film. H_α^* and SiH^* increase firstly and then decrease with the deposition pressure, the decrease of H_α^* and SiH^* under high pressure can be attributed to a high polymer formation which is not beneficial to the formation of high quality silicon film, and therefore the passivation effect of silicon films decreases under high pressures. H_α^* and SiH^* increase with power density, and are saturated when the power density is 150 mW/cm²; for this the quality and passivation effect of the silicon film begin to decrease, the passivation effect of the silicon film at a power density of 50 mW/cm² is poor, which may be due to the low concentration of atomic H being unable to fully passivate the dangling bonds at the silicon surface.
Keywords： silicon film heterojunction optical emission spectroscopy passivation