Review on Metallization Approaches for High-Efficiency Silicon Heterojunction Solar Cells

Abstract

Crystalline silicon (c-Si) heterojunction (HJT) solar cells are one of the promising technologies for next-generation industrial high-efficiency silicon solar cells, and many efforts in transferring this technology to high-volume manufacturing in the photovoltaic (PV) industry are currently ongoing. Metallization is of vital importance to the PV performance and long-term reliability of HJT solar cells. In this review, we summarize the development status of metallization approaches for high-efficiency HJT solar cells. For conventional screen printing technology, to avoid the degradation of the passivation properties of the amorphous silicon layer, a low-temperature-cured (< 250 ℃) paste and process are needed. This process, in turn, leads to high line/contact resistances and high paste costs. To improve the conductivity of electrodes and reduce the metallization cost, multi-busbar, fine-line printing, and low-temperature-cured silver-coated copper pastes have been developed. In addition, several potential metallization technologies for HJT solar cells, such as the Smart Wire Contacting Technology, pattern transfer printing, inkjet/FlexTrailprinting, and copper electroplating, are discussed in detail. Based on the summary, the potential and challenges of these metallization technologies for HJT solar cells are analyzed.

Keywords

Silicon solar cells / Passivating-contact / Heterojunction / Metallization / Electrode

References

[1] Chavali RVK, de Wolf S, Alam MA Device physics underlying silicon heterojunction and passivating-contact solar cells: a topical review. Prog Photovolt Res Appl, 2018, 26(4): 241-260.

[2] ITRPV consortium (2022) International technology roadmap for photovoltaic (ITRPV). https://www.vdma.org/viewer/-/v2article/render/50902381

[3] Allen TG, Bullock J, Yang XB, et al. Passivating contacts for crystalline silicon solar cells. Nat Energy, 2019, 4(11): 914-928.

[4] Yoshikawa K, Yoshida W, Irie T, et al. Exceeding conversion efficiency of 26% by heterojunction interdigitated back contact solar cell with thin film Si technology. Sol Energy Mater Sol Cells, 2017, 173: 37-42.

[5] Goodrich A, Hacke P, Wang Q, et al. A wafer-based monocrystalline silicon photovoltaics road map: utilizing known technology improvement opportunities for further reductions in manufacturing costs. Sol Energy Mater Sol Cells, 2013, 114: 110-135.

[6] Zhao J, König M, Wissen A et al (2017) > 23% silicon heterojunction solar cells in Meyer Burger's Demo line: results of pilot production on mass production tools. In: IEEE 44th photovoltaic specialist conference. Washington, DC, pp 1752–1754. https://doi.org/10.1109/PVSC.2017.8366365

[7] Mette A New concepts for front side metallization of industrial silicon solar cells, 2007 Baden-Württemberg University of Freiburg

[8] de Wolf S, Kondo M Nature of doped a-Si: H/c-Si interface recombination. J Appl Phys, 2009, 105(10

[9] Taguchi M, Yano A, Tohoda S, et al. 24.7% record efficiency HIT solar cell on thin silicon wafer. IEEE J Photovolt, 2014, 4(1): 96-99.

[10] Liu ZX (2022) HJT vs PERC+TOPCon: opportunities and challenges. In: 19th China photovoltaic academic conference. China

[11] Ru XN, Qu MH, Wang JQ, et al. 25.11% efficiency silicon heterojunction solar cell with low deposition rate intrinsic amorphous silicon buffer layers. Sol Energy Mater Sol Cells, 2020, 215: 110643.

[12] Shen WZ, Zhao YX, Liu F Highlights of mainstream solar cell efficiencies in 2021. Front Energy, 2022, 16(1): 1-8.

[13] LONGi (2022) 26.50%! LONGi sets new world record for HJT cell efficiency. WeChat official account of LONGi. https://mp.weixin.qq.com/s/QU7e18I2uuKCo_E3Wodm-Q. https://mp.weixin.qq.com/s/QU7e18I2uuKCo_E3Wodm-Q.Accessed25June2022

[14] Savin H, Repo P, von Gastrow G, et al. Black silicon solar cells with interdigitated back-contacts achieve 22.1% efficiency. Nat Nanotechnol, 2015, 10(7): 624-628.

[15] Zarede T, Lidjici H, Mahrane A, et al. 3D numerical simulation of bifacial heterojunction silicon p-type solar cell. SILICON, 2018, 10(4): 1745-1753.

[16] Verlinden PJ, Aleman M, Posthuma N, et al. Simple power-loss analysis method for high-efficiency interdigitated back contact (IBC) silicon solar cells. Sol Energy Mater Sol Cells, 2012, 106: 37-41.

[17] Rahman T, To A, Pollard ME, et al. Minimising bulk lifetime degradation during the processing of interdigitated back contact silicon solar cells. Prog Photovolt Res Appl, 2018, 26(1): 38-47.

[18] Bonilla RS, Hoex B, Wilshaw PR Special issue: surface and interface passivation in crystalline silicon solar cells. Sol Energy Mater Sol Cells, 2020, 213.

[19] Bivour M, Steinkemper H, Jeurink J, et al. Rear emitter silicon heterojunction solar cells: fewer restrictions on the optoelectrical properties of front side TCOs. Energy Procedia, 2014, 55: 229-234.

[20] Stuckelberger M, Biron R, Wyrsch N, et al. Review: progress in solar cells from hydrogenated amorphous silicon. Renew Sustain Energy Rev, 2017, 76: 1497-1523.

[21] Hermle M, Feldmann F, Bivour M, et al. Passivating contacts and tandem concepts: approaches for the highest silicon-based solar cell efficiencies. Appl Phys Rev, 2020, 7(2

[22] Panigrahi J, Komarala VK Progress on the intrinsic a-Si: H films for interface passivation of silicon heterojunction solar cells: a review. J Non Cryst Solids, 2021, 574.

[23] Olibet S, Vallat-Sauvain E, Ballif C Model for a-Si: H/c-Si interface recombination based on the amphoteric nature of silicon dangling bonds. Phys Rev B, 2007, 76(3

[24] Adachi D, Hernández JL, Yamamoto K Impact of carrier recombination on fill factor for large area heterojunction crystalline silicon solar cell with 25.1% efficiency. Appl Phys Lett, 2015, 107(23): 233506.

[25] Bivour M, Schröer S, Hermle M Numerical analysis of electrical TCO/a-Si: H(p) contact properties for silicon heterojunction solar cells. Energy Procedia, 2013, 38: 658-669.

[26] Khokhar MQ, Hussain SQ, Kim S, et al. Review of rear emitter silicon heterojunction solar cells. Trans Electr Electron Mater, 2020, 21(2): 138-143.

[27] Nogay G, Seif JP, Riesen Y, et al. Nanocrystalline silicon carrier collectors for silicon heterojunction solar cells and impact on low-temperature device characteristics. IEEE J Photovolt, 2016, 6(6): 1654-1662.

[28] Lei C, Peng CW, Zhong J, et al. Phosphorus treatment to promote crystallinity of the microcrystalline silicon front contact layers for highly efficient heterojunction solar cells. Sol Energy Mater Sol Cells, 2020, 209.

[29] Ling ZP, Ge J, Mueller T, et al. Optimisation of p-doped μc-Si: H emitter layers in crystalline-amorphous silicon heterojunction solar cells. Energy Procedia, 2012, 15: 118-128.

[30] Sharma M, Panigrahi J, Komarala VK Nanocrystalline silicon thin film growth and application for silicon heterojunction solar cells: a short review. Nanoscale Adv, 2021, 3(12): 3373-3383.

[31] Green MA Solar cells: operating principles, technology, and system applications, 1998 Kensington University of New South Wales

[32] Zou S, Ye XY, Wu CK, et al. Complementary etching behavior of alkali, metal-catalyzed chemical, and post-etching of multicrystalline silicon wafers. Prog Photovolt Res Appl, 2019, 27(6): 511-519.

[33] Martini L, Serenelli L, Menchini F, et al. Silicon heterojunction solar cells toward higher fill factor. Prog Photovolt Res Appl, 2020, 28(4): 307-320.

[34] Schubert G (2006) Thick film metallisation of crystalline silicon solar cells: mechanisms, models and applications. University of Konstanz, Baden-Württemberg, Germany. https://www.semanticscholar.org/paper/cd60620c1e95b462500222f7b57b343eeb5de4cf

[35] Rodofili A, Wolke W, Kroely L, et al. Laser transfer and firing of NiV seed layer for the metallization of silicon heterojunction solar cells by Cu-plating. Sol RRL, 2017, 1(8): 1700085.

[36] Sun ZQ, Chen XQ, He YC, et al. Toward efficiency limits of crystalline silicon solar cells: recent progress in high-efficiency silicon heterojunction solar cells. Adv Energy Mater, 2022, 12(23): 2270094.

[37] Wenzel T, Lorenz A, Lohmüller E, et al. Progress with screen printed metallization of silicon solar cells—towards 20 μm line width and 20 mg silver laydown for PERC front side contacts. Sol Energy Mater Sol Cells, 2022, 244.

[38] Potts SJ, Phillips C, Jewell E, et al. High-speed imaging the effect of snap-off distance and squeegee speed on the ink transfer mechanism of screen-printed carbon pastes. J Coat Technol Res, 2020, 17(2): 447-459.

[39] Liang L, Li ZG, Cheng LK, et al. Microstructural characterization and current conduction mechanisms of front-side contact of n-type crystalline Si solar cells with Ag/Al pastes. J Appl Phys, 2015, 117(21

[40] Khanna A, Ling ZP, Shanmugam V et al (2013) Screen printed metallisation for silicon heterojunction solar cells. In: 28th European PV solar energy conference and exhibition. Villepinte, Frankreich, pp 1336–1339

[41] Chen DP, Zhao L, Diao HW, et al. Choice of the low-temperature sintering Ag paste for a-Si: H/c-Si heterojunction solar cell based on characterizing the electrical performance. J Alloys Compd, 2015, 618: 357-365.

[42] Bai JG, Zhang ZZ, Calata JN et al (2005) Low-temperature sintering of nanoscale silver pastes for high-performance and highly-reliable device interconnection. In: Proceedings of ASME 2005 international mechanical engineering congress and exposition. Florida, pp 415–424. https://doi.org/10.1115/IMECE2005-79187

[43] Schube J Metallization of silicon solar cells with passivating contacts, 2020 Baden-Württemberg University of Freiburg

[44] Kim MI, Choi EB, Lee JH Improved sinter-bonding properties of silver-coated copper flake paste in air by the addition of sub-micrometer silver-coated copper particles. J Mater Res Technol, 2020, 9(6): 16006-16017.

[45] Zhang RW, Lin W, Lawrence K, et al. Highly reliable, low cost, isotropically conductive adhesives filled with Ag-coated Cu flakes for electronic packaging applications. Int J Adhesion Adhes, 2010, 30(6): 403-407.

[46] Körner S, Waltinger A, Partsch U et al (2016) High performance silver polymer pastes for SHJ cells.Publica.fraunhofer.de.https://publica.fraunhofer.de/starweb/servlet.starweb?path=epub0.web&search=N-421177

[47] Li YM, Kim HS, Yi J, et al. Improved electrical performance of low-temperature-cured silver electrode for silicon heterojunction solar cells. IEEE J Photovolt, 2018, 8(4): 969-975.

[48] Wang DL (2022) HJT low temperature metallization technology. In: 19th China photovoltaic academic conference, China

[49] Chung K, Bang J, Thacharon A, et al. Non-oxidized bare copper nanoparticles with surface excess electrons in air. Nat Nanotechnol, 2022, 17(3): 285-291.

[50] Perelaer J, Smith PJ, Mager D, et al. Printed electronics: The challenges involved in printing devices, interconnects, and contacts based on inorganic materials. J Mater Chem, 2010, 20(39): 8446.

[51] Yongqiang X, Baojiao G, Jianfeng G The theory of thermodynamics for chemical reactions in dispersed heterogeneous systems. J Colloid Interface Sci, 1997, 191(1): 81-85.

[52] Wang B, Ji Z, Zimone FT, et al. A technique for sputter coating of ceramic reinforcement particles. Surf Coat Technol, 1997, 91(1–2): 64-68.

[53] Xu XR, Luo XJ, Zhuang HR, et al. Electroless silver coating on fine copper powder and its effects on oxidation resistance. Mater Lett, 2003, 57(24–25): 3987-3991.

[54] Chen KT, Ray D, Peng YH, et al. Preparation of Cu–Ag core-shell particles with their anti-oxidation and antibacterial properties. Curr Appl Phys, 2013, 13(7): 1496-1501.

[55] Zhang Q, Liang SH, Zhuo LC Fabrication and properties of the W-30wt%Cu gradient composite with W@WC core-shell structure. J Alloys Compd, 2017, 708: 796-803.

[56] Shin J, Kim H, Song KH, et al. Synthesis of silver-coated copper particles with thermal oxidation stability for a solar cell conductive paste. Chem Lett, 2015, 44(9): 1223-1225.

[57] Liu JH, Wang K, Yu FW, et al. A paste based on Cu@Sn@Ag particles for Die attachment under ambient atmosphere in power device packaging. J Mater Sci Mater Electron, 2020, 31(3): 1808-1816.

[58] Sun HP, Wang KJ, Cai XL, et al. Preparation and performance of silver coated copper powder. Adv Mater Res, 2013, 750–752: 1057-1062.

[59] Schube J, Fellmeth T, Jahn M, et al. Advanced metallization with low silver consumption for silicon heterojunction solar cells. AIP Conf Proc, 2019, 2156(1

[60] Hong W (2022) Research direction and progress of low-temperature paste for high-efficiency heterojunction cells. In: 19th China photovoltaic academic conference, China

[61] Dhamrin M (2021) Low cost metallization approaches for advance solar cell structures. In: 17th China SoG Silicon and PV Power conference. Suzhou, China

[62] Kim SY, Kim MI, Lee JH Pressure-assisted sinter-bonding characteristics at 250 ℃ in air using bimodal Ag-coated Cu particles. Electron Mater Lett, 2020, 16(3): 293-298.

[63] Schneider A, Rubin L, Rubin G (2006) Solar cell efficiency improvement by new metallization techniques—the Day4 electrode concept. In: IEEE 4th world conference on photovoltaic energy conference. Waikoloa, HI, USA, pp 1095–1098. https://doi.org/10.1109/WCPEC.2006.279333

[64] Faes A, Despeisse M, Levrat J et al (2014) SmartWire solar cell interconnection technology. In: Proceedings of the 29th European photovoltaic solar energy conference, Amsterdam, Niederlande, pp 2555–2561

[65] Braun S, Micard G, Hahn G Solar cell improvement by using a multi busbar design as front electrode. Energy Procedia, 2012, 27: 227-233.

[66] Zhao J, König M, Yao Y et al (2018) >24% silicon heterojunction solar cells on Meyer burger's on mass production tools and how wafer material impacts cell parameters. In: IEEE 7th world conference on photovoltaic energy conversion (WCPEC), Waikoloa, pp 1514–1519. https://doi.org/10.1109/PVSC.2018.8547908

[67] Lossen J, Matusovsky M, Noy A, et al. Pattern transfer printing (PTP™) for c-Si solar cell metallization. Energy Procedia, 2015, 67: 156-162.

[68] Adrian A, Rudolph D, Lossen J et al (2018) Benefits of pattern transfer printing method for finger metallization on silicon solar cells. In: Proceedings of the 35th European photovoltaic solar energy conference and exhibition, Brussels, pp 24–27

[69] Mayberry R, Chandrasekaran V Metallization contributions, requirements, and effects related to pattern transfer printing (PTP™) on crystalline silicon solar cells. AIP Conf Proc, 2019, 2156(1

[70] Geissbühler J, Faes A, Lachowicz A et al (2017) Metallization techniques and interconnection schemes for high efficiency silicon heterojunction PV. PV Tech (pv-tech.org). https://www.pv-tech.org/technical-papers/metallization-techniques-and-interconnection-schemes-for-high-efficiency-silicon-heterojunction-pv/

[71] Tous L (2014) Nickel/copper plated contacts as an alternative to silver screen printing for the front side metallization of industrial high efficiency silicon solar cells. KU Leuven—Faculty of Engineering, Heverlee, Belgium

[72] JBAO Technology Ltd. (2022) Patented copper electroplating equipment. www.jbao-tech.com, http://www.jbao-tech.com/Cn/ProductView, http://www.jbao-tech.com/Cn/ProductView.Accessed6June2022

[73] Geissbühler J, de Wolf S, Faes A, et al. Silicon heterojunction solar cells with copper-plated grid electrodes: Status and comparison with silver thick-film techniques. IEEE J Photovolt, 2014, 4(4): 1055-1062.

[74] Li ZT, Hsiao PC, Zhang W, et al. Patterning for plated heterojunction cells. Energy Procedia, 2015, 67: 76-83.

[75] Yu J, Li JJ, Zhao YL, et al. Copper metallization of electrodes for silicon heterojunction solar cells: process, reliability and challenges. Sol Energy Mater Sol Cells, 2021, 224.

[76] Yu J, Bian JT, Liu YC, et al. Patterning and formation of copper electroplated contact for bifacial silicon hetero-junction solar cell. Sol Energy, 2017, 146: 44-49.

[77] Glatthaar M, Rohit R, Rodofili A, et al. Novel plating processes for silicon heterojunction solar cell metallization using a structured seed layer. IEEE J Photovolt, 2017, 7(6): 1569-1573.

[78] Hatt T, Kluska S, Yamin M, et al. Native oxide barrier layer for selective electroplated metallization of silicon heterojunction solar cells. Sol RRL, 2019, 3(6): 1900006.

[79] Hatt T, Mehta VP, Bartsch J, et al. (2018) Novel mask-less plating metallization route for bifacial silicon heterojunction solar cells. AIP Conf Proc, 1999, 1.

[80] Adachi D, Terashita T, Uto T, et al. Effects of SiO_x barrier layer prepared by plasma-enhanced chemical vapor deposition on improvement of long-term reliability and production cost for Cu-plated amorphous Si/crystalline Si heterojunction solar cells. Sol Energy Mater Sol Cells, 2017, 163: 204-209.

[81] Dabirian A, Lachowicz A, Schüttauf JW, et al. Metallization of Si heterojunction solar cells by nanosecond laser ablation and Ni–Cu plating. Sol Energy Mater Sol Cells, 2017, 159: 243-250.

[82] Yu J, Zhang LP, Chen T, et al. Dual-function light-trapping: selective plating mask of SiO_x/SiN_x stacks for silicon heterojunction solar cells. Sol RRL, 2019, 3(3): 1800261.

[83] Li JJ, Yu J, Chen T, et al. In-situ formation of indium seed layer for copper metallization of silicon heterojunction solar cells. Sol Energy Mater Sol Cells, 2020, 204.