An Improved Process for Bifacial n-PERT Solar Cells Fabricated with Phosphorus Activation and Boron Diffusion in One-step High Temperature

Abstract

The bifacial n-PERT (Passivated Emitter Rear Totally diffused) solar cells were fabricated using a simplified process in which the activation of ion-implanted phosphorus and boron diffusion were performed simultaneously in a high-temperature process. For further efficiency improvement, the rear side doping level was regulated by applying two different implantation doses and the chemical etching step of boron rich layer (BRL) was added, and their effects on cell performance were investigated. The solar cells average efficiency reaches 20.35% with a bifaciality factor of 90% by optimizing rear side doping level, which can be explained by the decrease of Auger recombination. And it is further enhanced to 20.74% by removing the front side BRL due to the improvement of surface passivation and bulk lifetime. The improved fabrication process possesses the advantages of low complexity and cost and high cell efficiency and bifaciality factor which could provide a promising way to the commercial production of bifacial n-PERT solar cells.

Keywords

n-PERT solar cells / ion implantation / diffusion / bifacial structure

References

[1] Fischer M. International Technology Roadmap for Photovoltaic (ITRPV), (11th ed.), 2020, available at https://itrpv.vdma.org/download

[2] Green MA. Solar Cell Efficiency Tables (Version 38)[J]. Prog. Photovolt. Res. Appl., 2011, 19: 565-572.

[3] Glunz SW, Rein S, Lee JY, et al. Minority Carrier Lifetime Degradation in Boron-doped Czochralski Silicon[J]. J. Appl. Phys., 2001, 90(5): 2 397-2 404.

[4] Schmidt J. Light-induced Degradation in Crystalline Silicon Solar Cells[J]. Solid State Phenom., 2004, 95: 187-196.

[5] Xiao S, Xu S. High-efficiency Silicon Solar Cells-materials and Devices Physics[J]. Crit. Rev. Solid State Mater Sci., 2014, 39(4): 277-317.

[6] Xiao SQ, Xu S, Ostrikov K. Low-temperature Plasma Processing for Si Photovoltaics[J]. Mater. Sci. Eng. R-Rep., 2014, 78: 1-29.

[7] Zhao J, Wang A, Altermatt PP, et al. High Efficiency PERT Cells on n-type Silicon Substrates[C]. In: Conference Record of the Twenty-Ninth IEEE Photovoltaic Spec. Conf., 2002: 218–221

[8] Mueller T, Schwertheim S, Mueller N, et al. High Efficiency Silicon Heterojunction Solar Cell Using Novel Structure[C]. In: 2010 35th IEEE Photovoltaic Spec. Conf., 2010: 000683–000688

[9] Cousins PJ, Smith DD, Luan HC, et al. Generation 3: Improved Performance at Lower Cost[C]. In: 2010 35th IEEE Photovoltaic Spec. Conf., 2010: 000275–000278

[10] Ohtsuka H, Sakamoto M, Tsutsui K, et al. Bifacial Silicon Solar Cells with 21.3% Front Efficiency and 19.8% Rear Efficiency[J]. Prog. Photovolt. Res. Appl., 2000, 8(4): 385-390.

[11] Green MA. The Passivated Emitter and Rear Cell (PERC): From Conception to Mass Production[J]. Sol. Energy Mater. Sol. Cells, 2015, 143: 190-197.

[12] Shanmugam V, Chen N, Yan X, et al. Impact of the Manufacturing Process on the Reverse-bias Characteristics of High-efficiency n-type Bifacial Silicon Wafer Solar Cells[J]. Sol. Energy Mater. Sol. Cells, 2019, 191: 117-122.

[13] Blévin T, Lanterne A, Grange B, et al. Development of Industrial Processes for the Fabrication of High Efficiency n-type PERT Cells[J]. Sol. Energy Mater. Sol. Cells, 2014, 131: 24-29.

[14] Wei Q, Zhang S, Yu S, et al. High Efficiency n-PERT Solar Cells by B/P Co-diffusion Method[J]. Energy Procedia, 2017, 124: 700-705.

[15] Meier S, Maier S, Demberger C, et al. Fast Co-diffusion Process for Bifacial n-type Solar Cells[J]. Solar RRL, 2017, 1(1): 1600005

[16] Shimizu S, Hsu SP, Du CH, et al. Screen Printable Boron Doping Paste and Its Process for n-type PERT Solar Cells[J]. IEEE J. Photovolt., 2018, 8(2): 483-486.

[17] Ryu K, Madani K, Rohatgi A, et al. High Efficiency Screen-printed n-type Silicon Solar Cell Using Co-diffusion of APCVD Boron Emitter and POCl3 Back Surface Field[J]. Curr. Appl. Phys., 2018, 18(2): 231-235.

[18] Yin HP, Tang WS, Zhang JB, et al. Screen-printed n-type Si Solar Cells with Laser-doped Selective Back Surface Field[J]. Solar Energy, 2021, 220: 211-216.

[19] Lanterne A, Le Perchec J, Gall S, et al. Understanding of the Annealing Temperature Impact on Ion Implanted Bifacial n-type Solar Cells to Reach 20.3% Efficiency[J]. Prog. Photovolt.: Res. Appl., 2015, 23(11): 1 458-1 465.

[20] Kiefer F, Peibst R, Ohrdes T, et al. Influence of the Boron Emitter Profile on V_oc and J_sc Losses in Fully Ion Implanted n-type PERT Solar Cells[J]. Phys. Stat. Sol. (a), 2015, 212(2): 291-297.

[21] Milési F, Coig M, Lerat JF, et al. Homojunction Silicon Solar Cells Doping by Ion Implantation[J]. Nucl. Instruments Methods Phys. Res. Sect. B Beam Interact. with Mater. Atoms, 2017, 409: 53-59.

[22] Torregrosa F, Roux L, Lanterne A, et al. PULSION®-Solar, a Efficient and Cost Effective Plasma Immersion Ion Implantation Solution for Phosphorus and Boron Doping Needed for High Conversion Efficiency Silicon Solar Cells[C]. In: Proc. 22nd Int. Conf. Implantation Technol. (IIT), Würzburg, Germany, 2018: 180–183

[23] Lanterne A, Desrues T, Lorfeuvre C, et al. Plasma-immersion Ion Implantation: A Path to Lower the Annealing Temperature of Implanted Boron Emitters and Simplify PERT Solar Cell Processing[J]. Prog. Photovolt. Res. Appl., 2019, 27(12): 1 081-1 091.

[24] Kania D, Böscke TS, Braun M, et al. Pilot Line Production of Industrial High-efficient Bifacial n-type Silicon Solar Cells with Efficiencies Exceeding 20.6%[C]. In: Proc. Eur. Photovoltaic Spec. Conf., Paris, France, 2013: 1 383–1 385

[25] Kessler MA, Ohrdes T, Wolpensinger B, et al. Charge Carrier Lifetime Degradation in Cz Silicon through the Formation of a Boron-rich Layer during BBr₃ Diffusion Processes[J]. Semicond. Sci. Technol., 2010, 25(5): 055001

[26] Ryu K, Choi CJ, Park H, et al. Fundamental Understanding, Impact, and Removal of Boron-rich Layer on n-type Silicon Solar Cells[J]. Sol. Energy Mater. Sol. Cells, 2016, 146: 58-62.

[27] Peng ZW, Hsieh PT, Huang CJ, et al. Toward 21% Efficiency NPERT Solar Cells with Selective Back Surface Field Technique[J]. Energy Procedia, 2016, 92: 702-707.

[28] Ryu K, Kim S, Kim W, et al. Mass Production of Low-cost Screen-printed Bifacial n-type Si Solar Cells with BBr₃-diffused Front Emitter and Ion-implanted Back Surface Field[C]. In: 2016 43rd IEEE Photovoltaic Spec. Conf., 2016: 2 512–2 514

[29] Böscke T S, Kania D, Schöllhorn C, et al. Fully Ion Implanted and Coactivated Industrial n-type Cells with 20.5% Efficiency[J]. IEEE J. Photovolt., 2013, 4(1): 48-51.

[30] Lanterne A, Le Perchec J, Gall S, et al. 20.5% Efficiency on Large Area n-type PERT Cells by Ion Implantation[J]. Energy Procedia, 2014, 55: 437-443.

[31] Schrof J, Müller R, Reedy RC, et al. Impact of Implanted Phosphorus on the Diffusivity of Boron and Its Applicability to Silicon Solar Cells[J]. J. Appl. Phys., 2015, 118(4): 045702

[32] Green MA. Limits on the Open-circuit Voltage and Efficiency of Silicon Solar Cells Imposed by Intrinsic Auger Processes[J]. IEEE Trans. Electron Devices, 1984, 31(5): 671-678.

[33] Richter A, Glunz SW, Werner F, et al. Improved Quantitative Description of Auger Recombination in Crystalline Silicon[J]. Phys. Rev. B, 2012, 86(16): 165202

[34] Kreinin L, Bordin N, Karsenty A, et al. PV Module Power Gain due to Bifacial Design. Preliminary Experimental and Simulation Data[C]. In: 2010 35th IEEE Photovoltaic Spec. Conf., 2010: 002171–002175

[35] Chen CC, Lin CL, Chien JW, et al. High Efficiency on Boron Emitter n-type Cz Silicon Bifacial Cells with Industrial Process[J]. Energy Procedia, 2013, 38: 416-422.

[36] Duttagupta S, Lin F, Shetty KD, et al. Excellent Boron Emitter Passivation for High-efficiency Si Wafer Solar Cells Using AlO_x/SiN_x Dielectric Stacks Deposited in an Industrial Inline Plasma Reactor[J]. Prog. Photovolt. Res. Appl., 2013, 21(4): 760-764.

[37] Shi J, Li X, Song D, et al. Mass Production and Modeling of High Efficiency n-PERT Solar Cells with Ion Implanted BSF/selective-BSF[J]. Solar Energy, 2017, 142: 87-90.

[38] Fernandez-Robledo S, Nekarda J, Büchler A. A Laser Induced Forward Transfer Process for Selective Boron Emitters[J]. Sol. Energy Mater. Sol. Cells, 2017, 161: 397-406.