低成本衬底上晶体硅薄膜太阳电池的研究

【作者】 励旭东；

【导师】 马本堃；

【作者基本信息】 北京师范大学 ， 凝聚态物理， 2003， 博士

【摘要】 本文主要研究了低成本衬底上薄膜的生长以及薄膜太阳电池的制备。本文的主要工作包括三个部分：首先是在模拟低成本衬底（非活性重掺杂单晶硅衬底）上外延薄膜并制备太阳电池。其主要目的是检验外延系统、研究薄膜生长特性、研究薄膜太阳电池的设计和工艺；其次是陶瓷衬底上多晶硅薄膜的生长和区熔再结晶的研究；最后是颗粒硅带衬底上多晶硅薄膜太阳电池的制备。 作为在该项研究的先期工作，首先在非活性重掺杂单晶硅衬底上制备了薄膜太阳电池。研究了外延工艺、电池制备工艺对太阳电池性能的影响。实验中发现，在我们现有设备上，采用优化的工艺条件，可以获得低缺陷密度、高质量的单晶硅薄膜。通过上述研究并结合器件模拟的有关结果，设计了优化的电池结构和工艺条件。在此基础上制备的太阳电池效率达到15.12％(J_SC=30.45mA，V_OC=637.1mV，FF=0.7797)。该结果已属国际同类研究的先进水平。 其次，研究了多种非硅衬底（主要是陶瓷衬底）上多晶硅薄膜的生长。对薄膜形貌以及生长特性等进行了分析。提出了一种简化的区熔再结晶方法，利用这种方法在非硅衬底获得了晶粒尺寸达到毫米级、致密的籽晶层。该研究工作对今后陶瓷衬底薄膜太阳电池的研究打下了良好的基础。 作为本文的主要内容，对低成本的颗粒硅带衬底作了较详细的研究。分析了衬底特性、外延薄膜的生长规律和特性。采用加入重掺杂层、快速生长等办法减少衬底对薄膜的影响。对低成本衬底上薄膜电池的工艺，特别是氢退火效应、氮化硅的制备和特性等作了深入的研究。发现这些工艺对钝化薄膜太阳电池的缺陷和晶界，改善薄膜质量和电池性能有明显的作用。通过这些研究工作，在高纯度颗粒硅带衬底上采用直接生长方式制备的薄膜电池效率达到8.25％(J_SC=26.69mA／cm²，V_OC=506.8mV，FF=0.6101)，在低纯度衬底上制备的电池效率达到4.5％(J_SC=20.39mA／cm²，V_OC=386.9mV，FF=0.57)，这些结果已达到国外同更多还原

【Abstract】 The wide use of solar cells will be a feasible way to solve the energy and environmental protection problems. The development of solar cells is showing a tendency to improve efficiency and reduce cost. Silicon thin-film solar cells are considered the most promising cells in the future for their advantages, such as low cost, high efficiency, great stability, simple processing, and none-pollution.To achieve this aim, silicon thin film solar cells on low cost substrates are studied in this thesis. Three kinds of substrates are adopted in our work, include heavily doped mono-crystalline silicon wafer, ceramics, and silicon sheets from powder （SSP）.Firstly, crystalline silicon thin films were deposited on heavily doped mono-crystalline silicon wafer by rapid thermal chemical vapor deposition （RTCVD）. With the optimized deposition parameters, mono crystalline silicon films with low defects density were obtained. Based on experiments and computer simulations, optimized processing conditions for cells’ fabrication were achieved. The best conversion efficiency of 15.12% （Voc=637.1mV, Jsc=30.45mA/cm², FF=0.7797, AM=1.5G ） has been reached, which is close to the best result in the world.Secondly, growth and recrystallization of silicon films on ceramic substrates were studied. Heavily doped polycrystalline silicon thin films were deposited on low cost ceramics substrates by RTCVD. Compact and uniform films with grain size in the order of some micrometers were fabricated. By means of zone melting recrystallization （ZMR） method, polycrystalline silicon thin films with large grains and relative high carrier mobility were obtained, which could act as a seeding layer. The maximum grain of these films was about one millimeter in width and some millimeters in length, and hole mobility exceeded 50cm²/Vs. Active silicon films deposited on these seeding layers showed the same morphologies. These results show that these films have great potential for photovoltaic applications.Finally, low cost SSP substrates were used in our experiments. Poly-crystalline silicon thin films were deposited on SSP substrates directly without any intermediate layer. A P⁺ layer between active layer and substrate was applied as a barrier for defects and impurities, and relative high deposition rate was achieved. Suitable processing conditions for cells’ fabrication, such as phosphorous diffusion, hydrogen passivation, SiN_x anti-reflection coating deposited by plasma enhanced chemical deposition （PECVD） were also studied. Based on these works, efficiency of 8.25 % (J_sc=26.69mA/cm2, V_oc=506.8mV, FF=0.6101) and 4.5% (J_sc=20.39mA/cm², V_oc=386.9mV, FF=0.57) have been obtained on high-purity and low-purity SSP substrates respectively. These results reach the better level in the world.更多还原