Hydrogenated amorphous si deposition for high efficiency a-Si/c-Si heterojunction solar cells
Hydrogenated amorphous si deposition for high efficiency a-Si/c-Si heterojunction solar cells
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DOI：
10.1109/pvsc.2013.6744127
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发表时间：
2013-06
期刊：
影响因子：
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通讯作者：
Qi Wang;M. Page;Y. Ai;W. Nemeth;L. Roybal;Hao-Chih Yuan
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作者：
Qi Wang;M. Page;Y. Ai;W. Nemeth;L. Roybal;Hao-Chih Yuan
研究了在高效a-Si/c-Si异质结（HJ）太阳电池中，采用热丝化学气相沉积（HWCVD）和等离子体增强化学气相沉积（PECVD）方法沉积氢化非晶硅（a-Si：H）的差异。在HWCVD中，诸如硅烷的工艺气体从高温热灯丝分解。由于缺乏可能对c-Si表面造成损害的离子轰击，因此认为所得沉积是温和的。在PECVD中，工艺气体从高频电场分解，并且在a-Si：H沉积期间预期离子轰击。我们发现，a-Si：H钝化的高质量n型晶片的初始少数载流子寿命在HWCVD工艺中更高（约为ms），并且最终少数载流子寿命（在250°C退火后）在PECVD工艺中更高（超过几ms）。这些发现表明，在PECVD中的离子轰击的损伤并不像我们预期的那样有害;或者如果有损伤，它可以通过退火来修复。我们还推测，HWCVD本征a-Si：H层退火后的寿命没有进一步增加可能与沉积过程中热丝对衬底的直接加热有关。高衬底温度会促进外延硅生长，并将氢从a-Si/c-Si界面驱离，从而降低表面钝化质量。为了减少热效应，优选快门和低灯丝温度。通过优化工艺，我们能够使用PECVD工艺在未织构化的n型晶片上制造具有714 mV的高开路电压和大于19%的效率的HJ太阳能电池，并且独立地确认使用HWCVD工艺在织构化的n型晶片上的最佳效率为19.7%。
We study the differences in hydrogenated amorphous Si (a-Si:H) depositions between Hot-Wire Chemical Vapor Deposition (HWCVD) and Plasma Enhanced Chemical Vapor Deposition (PECVD) for high efficiency a-Si/c-Si heterojunction (HJ) solar cells. In HWCVD, process gases such as silane decompose from the high-temperature hot filament. The resulting deposition is thought to be gentle due to the lack of ion bombardment that may cause damage to c-Si surface. In PECVD, process gases decompose from a high frequency electric field and ion bombardment is expected during the a-Si:H deposition. We found that the initial minority carrier lifetime of a-Si:H passivated high-quality n-type wafer was higher (about a ms) with the HWCVD process, and the final minority carrier lifetime (after 250°C annealing) was higher (over a few ms) with the PECVD process. These findings suggest that the damage from the ion bombarding in PECVD is not as detrimental as we expected; or if there is damage, it can be repaired by the annealing. We also speculate that the lack of further increase of the lifetime after annealing with HWCVD intrinsic a-Si:H layer can be related to the direct substrate heating from the hot filament during the deposition. A high substrate temperature will promote epi-Si growth and drive hydrogen out of the a-Si/c-Si interface to decrease the quality of surface passivation. To reduce the heating effect, a shutter and a low filament temperature are preferred. With the optimized process, we were able to fabricate HJ solar cells with high open circuit voltage of 714 mV and efficiency greater than 19% on an un-textured n-type wafer using the PECVD process, and independently confirm best efficiency of 19.7% on textured n-type wafer with the HWCVD process.