快速热处理在太阳电池中的应用
摘要
太阳能是一种非常重要的可再生清洁能源,使用太阳电池发电是利用太阳能的重要途径之一,而制备低成本、高效率太阳能电池则是大规模利用太阳能电池发电的关键。本篇论文利用一种快速、节省能耗而且廉价的技术——快速热处理(Rapid Thermal Processing,RTP)技术,在国内率先成功地制备了具有较高光电转化效率的单晶硅太阳能电池。在三个重要的热处理环节(磷扩散制作P-N结、热氧化、电极烧结)采用了快速热处理法,电极制作环节采用了大规模生产线上常用的丝网印刷电极法。经过初步研究,用大面积的单晶硅片制备出转换效率为11%、开路电压为564.6 mV、短路电流密度为30.7 mA/cm~2的太阳电池。
在太阳电池制备过程中,发射极(p-n结)的制备是一个非常重要的环节,因此在这个过程中,我们着重研究了磷在硅中的扩散。实验中使用液态旋涂磷源(Spin-on-dopants,SOD)做为掺杂剂,利用RTP技术在不同时间、温度和气氛下进行了快速热扩散。处理后,利用四探针法(Four-Poim Probe,FPP)、扩展电阻法(Spreading Resistance Profiles,SRP)等研究了磷在硅中的扩散.下面是本论文研究工作的主要内容,及取得的主要成果:
1) 利用SRP和FPP对经过不同温度下,干氧、湿氧和氢气气氛下磷的扩散进行了研究,发现RTP系统并不适合在湿氧环境下进行快速热处理。通过对实验结果的分析,发现在RTP处理时,氧气对磷在硅中的扩散也有类似常规热处理时的氧化增强扩散效应。
2) 利用SRP和FPP研究了氧气和氩气气氛中,1050℃和900℃下RTP扩散不同时间的样品。结果表明,在氧气氛中、1050℃下RTP时,高能光子的增强扩散效应在扩散过程中不起主导作用,而在低温阶段(900℃),不管是氧气气氛还是氩气气氛中,高能光子增强扩散效应都在扩散过程中起主导作用。
3) 利用SRP和FPP研究了不同气氛、时间和温度的RTP处理后样品中磷的扩散情况及扩散深度随时间变化的规律。结果又一次验证了氧化增强扩散效应,并表明,氧气气氛下的磷扩散表现为两个阶段,在这两个阶段里,氧化增强扩散效应和光能光子增强扩散效应所起的作用发生了变化。
4) 利用RTP技术和工业上常用的丝网印刷电极方法在国内率先制备了具有
In this thesis, rapid thermal processing (RTP), a rapid and low-cost technique, was employed to fabricate mono-crystalline silicon solar cells. RTP was applied in the three important thermal processes, which were the p-n junction formation by phosphorous diffusion, thermal oxidation and contact formation. The electrode contacts were fabricated with the screen-printing technique, which was commonly used in the large-scale production lines. Up to now, a large area mono-crystalline silicon solar cell with high conversion efficiency has been fabricated successfully in domestic, and its conversion efficiency, open-circuit voltage, and short-circuit current density are 11%, 564.6 mV, and 30.7 mA/cm~2, respectively.Since the fabrication of emitters (p-n junctions) is a very important process in the whole solar cell fabrication processes, phosphorous diffusion in silicon has been extensively investigated. In the work, Spin-on-dopants (SOD), as dopants, thermally diffused in the rapid thermal processor with different dwell time, temperatures, and ambients. The behaviors of phosphorous diffusion in silicon were studied by Four-Point Probe (FPP), Spreading Resistance Profiles (SRP) and other equipments. The main research work and its achievements are as follows:1. Wet oxygen apparatus was developed by the author. Phosphorous diffusion in the RTP processor with different temperatures and ambients, including dry oxygen, wet oxygen and argon, was characterized by SRP and FPP. It was found that the RTP processor was not suitable for rapid thermal processing in the wet oxygen ambient and oxygen had an oxidation-enhanced-diffusion effect on the phosphorous diffusion in silicon under RTP as oxygen did in the conventional thermal process.2. After rapid thermal processing at 1050 ℃ and 900 ℃ with oxygen and argon ambients for different dwell time, the phosphorous diffusion was characterized by SRP and FPP. It was found that under RTP, the high energy photons' enhanced diffusion effect didn't dominate the diffusion process at 1050 ℃ in the oxygen ambient, while it did dominate the diffusion process at 900 ℃ either in oxygen
ambient or argon ambient.3. The dependence of phosphorous diffusion on the dwell time was researched by SRP and FPP after the samples were processed by RTP with different ambient, dwell time and temperatures. It was found that both the oxidation and high-energy photons could enhance the phosphorous diffusion under RTP.4. The mono-crystalline silicon solar cells with the conversion efficiency of 11% was fabricated by RTP.
在太阳电池制备过程中,发射极(p-n结)的制备是一个非常重要的环节,因此在这个过程中,我们着重研究了磷在硅中的扩散。实验中使用液态旋涂磷源(Spin-on-dopants,SOD)做为掺杂剂,利用RTP技术在不同时间、温度和气氛下进行了快速热扩散。处理后,利用四探针法(Four-Poim Probe,FPP)、扩展电阻法(Spreading Resistance Profiles,SRP)等研究了磷在硅中的扩散.下面是本论文研究工作的主要内容,及取得的主要成果:
1) 利用SRP和FPP对经过不同温度下,干氧、湿氧和氢气气氛下磷的扩散进行了研究,发现RTP系统并不适合在湿氧环境下进行快速热处理。通过对实验结果的分析,发现在RTP处理时,氧气对磷在硅中的扩散也有类似常规热处理时的氧化增强扩散效应。
2) 利用SRP和FPP研究了氧气和氩气气氛中,1050℃和900℃下RTP扩散不同时间的样品。结果表明,在氧气氛中、1050℃下RTP时,高能光子的增强扩散效应在扩散过程中不起主导作用,而在低温阶段(900℃),不管是氧气气氛还是氩气气氛中,高能光子增强扩散效应都在扩散过程中起主导作用。
3) 利用SRP和FPP研究了不同气氛、时间和温度的RTP处理后样品中磷的扩散情况及扩散深度随时间变化的规律。结果又一次验证了氧化增强扩散效应,并表明,氧气气氛下的磷扩散表现为两个阶段,在这两个阶段里,氧化增强扩散效应和光能光子增强扩散效应所起的作用发生了变化。
4) 利用RTP技术和工业上常用的丝网印刷电极方法在国内率先制备了具有
In this thesis, rapid thermal processing (RTP), a rapid and low-cost technique, was employed to fabricate mono-crystalline silicon solar cells. RTP was applied in the three important thermal processes, which were the p-n junction formation by phosphorous diffusion, thermal oxidation and contact formation. The electrode contacts were fabricated with the screen-printing technique, which was commonly used in the large-scale production lines. Up to now, a large area mono-crystalline silicon solar cell with high conversion efficiency has been fabricated successfully in domestic, and its conversion efficiency, open-circuit voltage, and short-circuit current density are 11%, 564.6 mV, and 30.7 mA/cm~2, respectively.Since the fabrication of emitters (p-n junctions) is a very important process in the whole solar cell fabrication processes, phosphorous diffusion in silicon has been extensively investigated. In the work, Spin-on-dopants (SOD), as dopants, thermally diffused in the rapid thermal processor with different dwell time, temperatures, and ambients. The behaviors of phosphorous diffusion in silicon were studied by Four-Point Probe (FPP), Spreading Resistance Profiles (SRP) and other equipments. The main research work and its achievements are as follows:1. Wet oxygen apparatus was developed by the author. Phosphorous diffusion in the RTP processor with different temperatures and ambients, including dry oxygen, wet oxygen and argon, was characterized by SRP and FPP. It was found that the RTP processor was not suitable for rapid thermal processing in the wet oxygen ambient and oxygen had an oxidation-enhanced-diffusion effect on the phosphorous diffusion in silicon under RTP as oxygen did in the conventional thermal process.2. After rapid thermal processing at 1050 ℃ and 900 ℃ with oxygen and argon ambients for different dwell time, the phosphorous diffusion was characterized by SRP and FPP. It was found that under RTP, the high energy photons' enhanced diffusion effect didn't dominate the diffusion process at 1050 ℃ in the oxygen ambient, while it did dominate the diffusion process at 900 ℃ either in oxygen
ambient or argon ambient.3. The dependence of phosphorous diffusion on the dwell time was researched by SRP and FPP after the samples were processed by RTP with different ambient, dwell time and temperatures. It was found that both the oxidation and high-energy photons could enhance the phosphorous diffusion under RTP.4. The mono-crystalline silicon solar cells with the conversion efficiency of 11% was fabricated by RTP.
引文
1 能源危机带来光伏产业巨大商机,website:http://blog. cnfol. com/tdl/articles/135685. html
2 R. R Mertens, R. J. Van Overstraeten, K. U. Leuven, Solar cell fabrication techniques for single and semicrystalline silicon substrates, International Journal of Solar Energy, 1984, 2(2): 121-140.
3 Centrotherm Elektrische Anlagen GmbH & Co. Website: www. centrotherm. de
4 R. B. Campbell, D. L. Meier, Simultaneous junction formation using a directed energy light source, J. Electrochem. Soc., 1986, 133(10): 2210-2211
5 A. Rohatgi, Z. Chen, P. Doshi, T. Pham and D. Ruby, et al. High-efficiency silicon solar cells by rapid thermal processing. Appl. Phys. Lett. 1994, 65(16): 2087-2089
6 R. A. Steeman, M. Lefrancois, RTP emitter diffusion in an industrial process, Conference Record of the 28th IEEE Photovoltaic Specialists Conference, Sep. 2000, p288-290.
2 R. R Mertens, R. J. Van Overstraeten, K. U. Leuven, Solar cell fabrication techniques for single and semicrystalline silicon substrates, International Journal of Solar Energy, 1984, 2(2): 121-140.
3 Centrotherm Elektrische Anlagen GmbH & Co. Website: www. centrotherm. de
4 R. B. Campbell, D. L. Meier, Simultaneous junction formation using a directed energy light source, J. Electrochem. Soc., 1986, 133(10): 2210-2211
5 A. Rohatgi, Z. Chen, P. Doshi, T. Pham and D. Ruby, et al. High-efficiency silicon solar cells by rapid thermal processing. Appl. Phys. Lett. 1994, 65(16): 2087-2089
6 R. A. Steeman, M. Lefrancois, RTP emitter diffusion in an industrial process, Conference Record of the 28th IEEE Photovoltaic Specialists Conference, Sep. 2000, p288-290.