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 [ Time:2014/4/2 ]
Series of process in preparation and functionalization of silicon nanowire (SiNW) arrays by ISSP
Author :LI Shuxin

Recently, researchers in the institute of solid state physics (ISSP), have made series of process in preparation, release and integrate transfer of silicon nanowire (SiNW) arrays. Moreover, on basis of this, solar cell devices which have significant photoelectric conversion performance and excellent stability have been fabricated.
Silicon as the core material of modern electronic elements, has important applications in the fields of microelectronics, photovoltaic, photoelectric, thermoelectric, and energy storage. The study of SiNW arrays is always a hot point, and the density of SiNW arrays is one of the determining factors to affect the information storage and other applications. However, the density of SiNWs is still limited by the density of pores in the AAO template which is extremely difficult to increase beyond the 1010/cm2 level. On the other hand, crystalline silicon has high hardness and poor bending performance, which greatly limits its application in the future conductive or portable electronic products.
Ph.D Da Yong TENG used the metal-assisted chemical etching(MACE) method to prepare SiNW arrays of high density via a new PS microspheres-based two-step template method. Through controlling the plasma etching treatment of PS microspheres and adjusting the content of Fe(NO3)3 solvent during the first template fabrication, he discovers that the density of Si nanowires can be increased to two times that of the single-layer PS microspheres and further to three times when a double layer of PS microspheres is introduced(Figure 1). In addition, he also finds that the density of SiNW arrays can be further increased by using small diameter PS microspheres. Ph.D Luo Wu proposes an effective method to automatically release SiNW arrays readily from Si wafer with a high integrity by an selective ammonia etching process, then transfers SiNW arrays to any accepted substrates(Figure 2), especially for the flexible substrates which has good bending properties, such as PET. Although the thickness of SiNW array films is only several micrometers, the absorption of the visible light is greater than 90% (Figure 3). The relevant results have been published in Langmuir (Langmuir 30, 2259, 2014) and Scientific Reports (Scientific Reports 4, 3940, 2014).
Ph.D Wei Wei HE further fabricates SiNW arrays/organic hybrid solar cells, and proposes a new interface treatment method to decrease the defect density effectively, then significantly improves the stability of the solar cells (Figure 4). The conversion efficiency of SiNW arrays hybrid solar cells fabricated by the traditional method would be lower than 10% after putting in the atmosphere environment for 24 hours without encapsulation, however, the cells that we made showed an average efficiency loss 45% during a period of five months. The relevant results have been published in Scientific Reports (Scientific Reports 4, 3715, 2014).
This work was supported by the National Basic Research Program of China (973 Program, Grant No. 2011CB302103), National Natural Science Foundation of China (Grant No.11274308), and the Hundred Talent Program of the Chinese Academy of Sciences.

Figure 1: A high density of SiNW arrays

Figure 2: Schematic illustrations of the fabrication procedure for auto-releasing SiNW arrays

Figure 3: Vertical transferring of the released SiNW arrays on flexible substrates and the corresponding absorption 
Figure 4: Stability of SiNA/PEDOT:PSS hybrid solar cells

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