24September2017

Materials and Electronics Engineering

Texturing multicrystalline Si solar cell using self-assembly Ni nanoparticle masks

Huijuan Geng1, Yen-Chun Wu2, Ayra Jagadhamma Letha2, Ying Wang1, Yafei Zhang1*, Huey-Liang Hwang1, 2*

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1Key Laboratory for Thin Film and Microfabrication of Ministry of Education, Department of Micro/Nano Electronics, Shanghai Jiao Tong University, Shanghai 200240, PR China

2Department of Electrical Engineering and Institute of Electronics Engineering, National Tsing Hua University, Hsinchu 300, Taiwan

Materials and Electronics Engineering 2015, 2:1

Publication Date (Web): February 2, 2015 (Article)

DOI:10.11605/mee-2-1

*Corresponding author. E-mail: This email address is being protected from spambots. You need JavaScript enabled to view it. ; This email address is being protected from spambots. You need JavaScript enabled to view it.

 

Abstract

 


Figure 1 Process of RIE texturing multicrystalline Si wafer using self-assembly Ni nanoparticle masks.
Surface texturing is indispensable to reduce optical reflectivity for silicon solar cells. Reactive ion etching technique using self-assembly Ni nanoparticle masks has been successfully developed in this work to texture the front surface of the multicrystalline Si wafers. Ni nanoparticles were assembled on the wafer surface by annealing the Ni thin film at 900 °C, which played a dominative role in controlling the morphology of textured structure. Experimental results indicate that the surface structure of the RIE textured wafer is nanopillar array, and the reflectance is significantly reduced to below 2% in the range of wavelength from 400 nm to 1000 nm. Moreover, a damage-free Si surface was recovered by incorporating improved cleaning and damage removal treatment. And the efficiency of the best solar cell with HNO3 treatment can be improved from 8.60 to 12.01%. To the best of our knowledge, this is the first demonstration of using Ni particle masks for mutlicrystalline Si solar cell fabrication. 

Keywords

Reactive ion etching, Ni nanoparticle masks, multicrystalline Si solar cell

 

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Introduction

      Novel surface structures for high efficiency crystalline silicon solar cells were investigated by Chen C.H. [1], and the highest efficiency of the modified grating monocrystalline Si solar cell reached 17.5%. It is noteworthy that the market share of multicrystalline Si solar cells in worldwide PV production is steadfastly increasing due to the high efficiency and low cost [2]. However, the efficiency of mc-Si solar cell is lower than that of monocrystalline Si solar cell, and still needs to be improved. One of the major performance limitations is the inability to effectively texture the front surface to enhance the light absorption [3, 4]. Anisotropic alkaline etching techniques, commonly used to texture monocrystalline Si wafers, are ineffective for multicrystalline Si wafer due to randomly orientated crystallites. It is thus indispensable, but still challenging, to develop various attempts that will isotropically texture the front surface, regardless of crystallographic orientation.

      Various texturing techniques, such as reactive ion etching (RIE) [5, 6], porous silicon etching [7], laser texturing [8], plasma immersion ion implantation [9] and photo-lithographically-defined etching [10], have been attempted to further reduce the surface reflectance of multicrystalline Si wafer. As a kind of plasma etching [11, 12], the RIE process is independent from crystallographic orientation, which is expected to significantly impact terrestrial photovoltaic technology, particularly in the field of mc-Si solar cell. Recently, RIE has gained increasing interest to achieve improved performance [13]. The maskless RIE process is appropriate to increase light trapping in the near IR spectral range, but the morphology of the textured surface is random [14].

      This work is focused on using RIE technique with self-assembly Ni nanoparticle masks to texture the front surface of multicrystalline Si to absorb more light, and Ni nanoparticles were self-aggregated by rapid thermal the Ni film evaporated on the SiO2 layer covered Si wafer, and used as masks, which played a crucial role in controlling the morphology of the textured structure. Ni nanoparticle masks adopted in this research is not only simple to control but also cheap in the fabrication of uniform nanostructure. And then the textured structure was formed by two step RIE process using CF4/Cl2 gases as available etching gases.

Experiments

      P-type mc-Si wafers with thickness of 200 ± 20 µm, 4 cm × 4 cm, and resistivity of 0.3-3 Ω-cm were employed in this work. The whole process of obtaining textured structure on multicrystalline Si wafer is described in Fig. 1, and can be summarized in the following steps. Firstly, the saw damage on the surface was removed by etching in CH3COOH:HNO3:H2O=3:2:1 solution for 10 s. Silicon oxide (~10 nm) buffered layer was deposited by plasma enhanced chemical vapor deposition (PECVD) under standard recipe, and used to avoid Ni doping into Si when being annealed at high temperature. Thirdly, Ni (~15 nm) thin film was deposited by E-gun evaporation and annealed at 900 °C for 1 min to aggregate, and grow up to form Ni nanoparticles. Then, using Ni nanoparticles as masks, wafers were etched to form the desired structure by RIE technique for 300 s. Finally, the Ni nanoparticles were removed with HNO3, HCl solutions and then the wafer cleaning was carried out by RCA process.

      The RIE textured wafer was subjected to phosphorus diffusion using POCl3 as the dopant source at 900 °Cfor 10 min to form the PN junction for solar cells as conventional cell fabrication protocol. All the wafers were subjected to edge etching and porous Si glass formed in the doping process were removed by buffer oxide etch. Silicon-nitride layer (ca. 80 nm) was grown by PECVD. Finally, Ag (front) electrode and Al (back) electrode were formed by screen printing technique and followed by firing at 900 °Cfor 10 s. Solar cells were obtained in the university laboratories.

      The RIE process is performed by Metal etcher (Japan Anelva ILD-4100). The surface structure was elucidated by scanning electron microscope (SEM), and the surface reflectance was examined by a UV-vis-NIR spectrophotometer equipped with an integrating sphere detector. The performances of the solar cells were determined under a one sun global solar spectrum of air mass (AM) 1.5 at 25 °C.

Figure 1 Process of RIE texturing multicrystalline Si wafer using self-assembly Ni nanoparticle masks.

Figure 1 Process of RIE texturing multicrystalline Si wafer using self-assembly Ni nanoparticle masks.

Results and discussion

      The adhesion between Ni and Si is too good to make Ni self-aggregated, so a buffer layer (SiO2 layer) deposited between Ni and Si layer is required to solve this problem. Besides, the thin oxide layer can also prevent the formation of NiSi2 compounds and facilitates the self-assembly of Ni nanoparticles from retaining the thermal power on SiO2 layer, it can avoid Ni doping into Si when being annealed at high temperature [15]. Figure 2a and b show SEM images of Ni nanoparticles formed by annealing the Ni thin film at 900 °C. The obtained Ni nanoparticles, having approx. size of 280 nm, are clearly observed. And the distance between Ni nanoparticles is about 225 nm. The sizes of Ni nanoparticles can be tuned by controlling the growth parameters of Ni nanoparticles, such as thickness of Ni thin film, annealing time and temperature. The obtained Ni nanoparticles are used as masks in the RIE process, which play a crucial role in controlling the morphology of the textured structure. A two-step RIE process is used to form the nanopillar structure. The first step is used to etch the Ni thin film between particles, and the second step is used to etch the multicrystalline Si. The parameter of RIE process used for obtaining the lowest reflectance of the sample is shown in Table1. Figure 2c and d exhibit the SEM images of the surface textured structure after RIE process, the nanopillars are about 570 nm in height and 300 nm in diameter.

Table 1 Parameters of RIE for obtaining the textured structure on multicrystalline Si wafer.

Figure 2 (a) and (b) Morphologies of self-assembly Ni nanoparticles, (c) and (d) morphologies of the obtained surface structures after the RIE process.

Figure 2 (a) and (b) Morphologies of self-assembly Ni nanoparticles, (c) and (d) morphologies of the obtained surface structures after the RIE process.

      The micro-nano structure as a rough surface has good antireflection for the scattering to light. Figure 3 shows the reflectance of planar multicrystalline Si wafer, pyramid structured monocrystalline Si wafer and RIE textured multicrystalline Si wafer. Compared with planar multicrystalline Si wafer, remarkable decrease of reflectivity is observed in RIE textured multicrystalline Si wafer. And it is noted that the reflectivity of RIE textured multicrystalline Si wafer is much lower than that of pyramid structured monocrystalline Si wafer, which is lower than that of conventional texture multicrystalline Si wafer. For obtained RIE textured structure, the reflectance is reduced to below 2 % in the range of wavelength from 400 nm to 1000 nm. As compared with the conventional acidic or alkaline texturing used in the industrial production line, the results indicate that the RIE process is very useful to decrease the reflection of the multicrystalline Si wafer.

Figure 3 Reflectance curves of planar multicrystalline Si wafer, pyramid structured monocrystalline Si wafer and RIE textured multicrystalline Si wafer.

Figure 3 Reflectance curves of planar multicrystalline Si wafer, pyramid structured monocrystalline Si wafer and RIE textured multicrystalline Si wafer.

      Despite widespread applicability of RIE process, it is well known that Si surface exposed to plasma process suffers from surface damage [16]. So surface damage can be induced during the RIE process, which could deteriorate the performance of solar cell. Wet-chemical etching has been observed to be best suited for the recovery process [17]. In this work, we have investigated damage removal etching in the HNO3/HF/H2O (50:1:20) solution. The sample was dipped into the HNO3/HF/H2O solution for 10 s to remove the RIE surface layer damage and then annealed at 550 °Cfor 1 h to remove the deep layer damage occurred during the RIE process. The obtained RIE textured structure is nanoscale, so Si3N4 layer could not passivate the textured surface completely. So an extra process dipping the sample into the HNO3 solution for 30 s also could be incorporated into this process flow to get a thin oxide film to passivate the RIE textured surface better. Figure 4 displays the illuminated J-V characteristics of the RIE textured solar cell: with and without HNO3 treatment process. The short circuit current (Jsc), open circuit (Voc), fill factor (FF) and conversion efficiency (Eff) are summarized. Compared with the solar cell without HNO3 treatment, it is obvious that the performance of the solar cell treated with HNO3 process is improved remarkably. Jsc is improved from 26.6 to 33.9 mA cm-2. And the efficiency is enhanced to 12.01 %. The results indicate that HNO3 treatment process could further remove the RIE damage to enhance the performance of the mc-Si solar cell, and the further optimization could help to get higher efficiency solar cells.

Figure 4 Illuminated J-V curves for RIE textured mc-Si solar cells: (a) without and (b) with HNO3 treatment.

Figure 4 Illuminated J-V curves for RIE textured mc-Si solar cells: (a) without and (b) with HNO3 treatment.

Conclusions

      RIE technique using self-assembly Ni nanoparticle mask has been developed to texture the front surface of mc-Si solar cell. The obtained Ni nanoparticles play a crucial role in controlling the morphology of the textured structure during the RIE process. The obtained textured structure significantly improves the antireflection and light trapping properties. By this process, the Eff and Jsc of the solar cell fabricated so far could reach to 12.01 % and 33.9 mA cm-2 respectively. Therefore, the optical and electrical properties demonstrate that this technique could be applied to mc-Si wafers to achieve higher efficiency by increasing the probability of absorption of photons and enhancing the photo-generated current in a conventional solar cell production line. 

References

1 C.H. Chen, Investigations on novel surface structures for high efficiency crystalline silicon solar cells [PhD]. National Tsing Hua University. 2012. 

2 D.H. Macdonald, A. Cuevas, M.J. Kerr, C. Samundsett, D. Ruby, S. Winderbaum, A. Leo, Texturing industrial multicrystalline silicon solar cells. Solar Energy 76, 277–283 (2004). doi:10.1016/j.solener.2003.08.019
3 Y.F. Zhang, H.J. Geng, Z.H. Zhou, J. Wu, Z.M. Wang, Y.Z. Zhang, Z.L. Li, L.Y. Zhang, Z. Yang, H.L. Hwang, Development of inorganic solar cells by nanotechnology. Nano-Micro Lett. 4, 124–134 (2012). doi:10.1007/BF03353703
4 S.H. Zhong, B.W. Liu, Y. Xia, J.H. Liu, J. Liu, Z.N. Shen, Z. Xu, C.B. Li, Influence of the texturing structure on the properties of black silicon solar cell. Sol. Energ. Mat. Sol. C. 108, 200–204 (2013). doi:10.1016/j.solmat.2012.10.001
5 J. Yoo, G. Yu, J. Yi, Large-area multicrystalline silicon solar cell fabrication using reactive ion etching (RIE). Sol. Energ. Mat. Sol. C. 95, 2–6 (2011). doi:10.1016/j.solmat.2010.03.029
6 W.A. Nositschka, O. Voigt, P. Manshanden, H. Kurz, Texturisation of multicrystalline silicon solar cells by RIE and plasma etching. Sol. Energ. Mat. Sol. C. 80, 227–237 (2003). doi:10.1016/j.solmat.2003.06.003
7 X. Li, P.W. Bohn, Metal-assisted chemical etching in HF/H2O2 produces porous silicon. Appl. Phys. Lett. 77, 2572–2574 (2000). doi:10.1063/1.1319191
8 M. Abbott, J. Cotter, Optical and electrical properties of laser texturing for high-efficiency solar cells. Prog. Photovolt. Res. Appl. 14, 225–235 (2006). doi:10.1002/pip.667
9 J. Liu, B.W. Liu, Z.N. Shen, J.H. Liu, S.H. Zhong, S. Liu, C.B. Li, Y. Xia, Characterization of PIII textured industrial multicrystalline silicon solar cells. Solar Energy 86, 3004–3008 (2012). doi:10.1016/j.solener.2012.07.006
10 J. Zhao, A. Wang, M.A. Green, F. Ferrazza, 19.8% efficient “honeycomb” textured multicrystalline and 24.4% monocrystalline silicon solar cells. Appl. Phys. Lett. 73, 1991–1993 (1998). doi:10.1063/1.122345
11 C. Cho, D. Kong, J.H. Oh, B. Kim, B. Lee, J. Lee, Surface texturing method for silicon solar cell using reactive ion etching with metal mesh. Phys. Status Solidi A 211, 1844–1849 (2014). doi:10.1002/pssa.201330545
12 W.A. Nositschka, C. Beneking, O. Voigt, H. Kurz, Texturisation of multicrystalline silicon wafers for solar cells by reactive ion etching through colloidal masks. Sol. Energ. Mat. Sol. C. 76, 155–166 (2003). doi:10.1016/S0927-0248(02)00214-3
13 K.S. Lee, M.H. Ha, J.H. Kim, J.W. Jeong, Damage-free reactive ion etch for high-efficiency large-area multi-crystalline silicon solar cells. Sol. Energ. Mat. Sol. C. 95, 66–68 (2011). doi:10.1016/j.solmat.2010.03.007
14 J. Yoo, J.S. Cho, S. Ahn, J. Gwak, A. Cho, Y.J. Eo, J.H. Yun, K. Yoon, J. Yi, Random reactive ion etching texturing techniques for application of multicrystalline silicon solar cells. Thin Solid Films 546, 275–278 (2013). doi:10.1016/j.tsf.2013.02.045
15 G.R. Lin, H.C. Kuo, H.S. Lin, C.C. Kao, Rapid self-assembly of Ni nanodots on Si substrate covered by a less-adhesive and heat-accumulated SiO2 layers. Appl. Phys. Lett. 89, 073018-3pp (2006). doi:10.1063/1.2336081
16 S. Schaefer, R. Lüdemann, Low damage reactive ion etching for photovoltaic applications. J. Vac. Sci. Technol. A 17, 749–754 (1999). doi:10.1116/1.581644
17 S.H. Zaidi, D.S. Ruby, J.M. Gee, Characterization of random reactive ion etched-textured silicon solar cells. IEEE Trans Electron Devices 48, 1200–1206 (2001). doi:10.1109/16.925248

Acknowledgements

The authors gratefully acknowledge financial support from National High-Tech R & D Program of China (863, No.2011AA050504), the National Natural Science Foundation of China (No. 61274051, No. 61376003, and No. 51272155), Shanghai Science and Technology Grant (No. 12nm0503800), and Ministry of Economic Affairs, Taiwan (No.102-EC-17-A-13-S1-173). The authors would like to thank Prof. Dong Xu and Dr. Poonam Sharma for their supports in experiments and discussion.

References

1 C.H. Chen, Investigations on novel surface structures for high efficiency crystalline silicon solar cells [PhD]. National Tsing Hua University. 2012. 
2 D.H. Macdonald, A. Cuevas, M.J. Kerr, C. Samundsett, D. Ruby, S. Winderbaum, A. Leo, Texturing industrial multicrystalline silicon solar cells. Solar Energy 76, 277–283 (2004). doi:10.1016/j.solener.2003.08.019

3 Y.F. Zhang, H.J. Geng, Z.H. Zhou, J. Wu, Z.M. Wang, Y.Z. Zhang, Z.L. Li, L.Y. Zhang, Z. Yang, H.L. Hwang, Development of inorganic solar cells by nanotechnology. Nano-Micro Lett. 4, 124–134 (2012). doi:10.1007/BF03353703
4 S.H. Zhong, B.W. Liu, Y. Xia, J.H. Liu, J. Liu, Z.N. Shen, Z. Xu, C.B. Li, Influence of the texturing structure on the properties of black silicon solar cell. Sol. Energ. Mat. Sol. C. 108, 200–204 (2013). doi:10.1016/j.solmat.2012.10.001
5 J. Yoo, G. Yu, J. Yi, Large-area multicrystalline silicon solar cell fabrication using reactive ion etching (RIE). Sol. Energ. Mat. Sol. C. 95, 2–6 (2011). doi:10.1016/j.solmat.2010.03.029
6 W.A. Nositschka, O. Voigt, P. Manshanden, H. Kurz, Texturisation of multicrystalline silicon solar cells by RIE and plasma etching. Sol. Energ. Mat. Sol. C. 80, 227–237 (2003). doi:10.1016/j.solmat.2003.06.003
7 X. Li, P.W. Bohn, Metal-assisted chemical etching in HF/H2O2 produces porous silicon. Appl. Phys. Lett. 77, 2572–2574 (2000). doi:10.1063/1.1319191
8 M. Abbott, J. Cotter, Optical and electrical properties of laser texturing for high-efficiency solar cells. Prog. Photovolt. Res. Appl. 14, 225–235 (2006). doi:10.1002/pip.667
9 J. Liu, B.W. Liu, Z.N. Shen, J.H. Liu, S.H. Zhong, S. Liu, C.B. Li, Y. Xia, Characterization of PIII textured industrial multicrystalline silicon solar cells. Solar Energy 86, 3004–3008 (2012). doi:10.1016/j.solener.2012.07.006
10 J. Zhao, A. Wang, M.A. Green, F. Ferrazza, 19.8% efficient “honeycomb” textured multicrystalline and 24.4% monocrystalline silicon solar cells. Appl. Phys. Lett. 73, 1991–1993 (1998). doi:10.1063/1.122345
11 C. Cho, D. Kong, J.H. Oh, B. Kim, B. Lee, J. Lee, Surface texturing method for silicon solar cell using reactive ion etching with metal mesh. Phys. Status Solidi A 211, 1844–1849 (2014). doi:10.1002/pssa.201330545
12 W.A. Nositschka, C. Beneking, O. Voigt, H. Kurz, Texturisation of multicrystalline silicon wafers for solar cells by reactive ion etching through colloidal masks. Sol. Energ. Mat. Sol. C. 76, 155–166 (2003). doi:10.1016/S0927-0248(02)00214-3
13 K.S. Lee, M.H. Ha, J.H. Kim, J.W. Jeong, Damage-free reactive ion etch for high-efficiency large-area multi-crystalline silicon solar cells. Sol. Energ. Mat. Sol. C. 95, 66–68 (2011). doi:10.1016/j.solmat.2010.03.007
14 J. Yoo, J.S. Cho, S. Ahn, J. Gwak, A. Cho, Y.J. Eo, J.H. Yun, K. Yoon, J. Yi, Random reactive ion etching texturing techniques for application of multicrystalline silicon solar cells. Thin Solid Films 546, 275–278 (2013). doi:10.1016/j.tsf.2013.02.045
15 G.R. Lin, H.C. Kuo, H.S. Lin, C.C. Kao, Rapid self-assembly of Ni nanodots on Si substrate covered by a less-adhesive and heat-accumulated SiO2 layers. Appl. Phys. Lett. 89, 073018-3pp (2006). doi:10.1063/1.2336081
16 S. Schaefer, R. Lüdemann, Low damage reactive ion etching for photovoltaic applications. J. Vac. Sci. Technol. A 17, 749–754 (1999). doi:10.1116/1.581644
17 S.H. Zaidi, D.S. Ruby, J.M. Gee, Characterization of random reactive ion etched-textured silicon solar cells. IEEE Trans Electron Devices 48, 1200–1206 (2001). doi:10.1109/16.925248

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Additional Info

  • Type of Publishing: JOUR - Journal
  • Title:

    Texturing multicrystalline Si solar cell using self-assembly Ni nanoparticle masks

  • Author: Huijuan Geng, Yen-Chun Wu, Ayra Jagadhamma Letha, Ying Wang, Yafei Zhang, Huey-Liang Hwang
  • Year: 2015
  • Volume: 2
  • Issue: 1
  • Journal Name: Materials and Electronics Engineering
  • Publisher: Nicety Press Company Limited
  • ISSN: 2410-1648
  • URL: http://www.meej.org/volume-2/february-2015/item/370-texturing-multicrystalline-si-solar-cell-using-self-assembly-ni-nanoparticle-masks
  • Abstract:

        Surface texturing is indispensable to reduce optical reflectivity for silicon solar cells. Reactive ion etching technique using self-assembly Ni nanoparticle masks has been successfully developed in this work to texture the front surface of the multicrystalline Si wafers. Ni nanoparticles were assembled on the wafer surface by annealing the Ni thin film at 900 °C, which played a dominative role in controlling the morphology of textured structure. Experimental results indicate that the surface structure of the RIE textured wafer is nanopillar array, and the reflectance is significantly reduced to below 2 % in the range of wavelength from 400 nm to 1000 nm. Moreover, a damage-free Si surface was recovered by incorporating improved cleaning and damage removal treatment. And the efficiency of the best solar cell with HNO3 treatment can be improved from 8.60 to 12.01 %. To the best of our knowledge, this is the first demonstration of using Ni particle masks for mutlicrystalline Si solar cell fabrication.

  • Publish Date: Monday, 02 February 2015
  • Start Page: 1
  • DOI: 10.11605/mee-2-1