Hostname: page-component-cd9895bd7-hc48f Total loading time: 0 Render date: 2024-12-23T12:06:46.760Z Has data issue: false hasContentIssue false
  • English
  • Français

Polycrystalline silicon passivated tunneling contacts for high efficiency silicon solar cells

Published online by Cambridge University Press:  23 March 2016

Bill Nemeth ,
David L. Young ,
Matthew R. Page ,
Vincenzo LaSalvia ,
Steve Johnston ,
Robert Reedy  and
Paul Stradins
Bill Nemeth*
Affiliation:
National Renewable Energy Laboratory, Golden, Colorado 80401, USA
David L. Young
Affiliation:
National Renewable Energy Laboratory, Golden, Colorado 80401, USA
Matthew R. Page
Affiliation:
National Renewable Energy Laboratory, Golden, Colorado 80401, USA
Vincenzo LaSalvia
Affiliation:
National Renewable Energy Laboratory, Golden, Colorado 80401, USA
Steve Johnston
Affiliation:
National Renewable Energy Laboratory, Golden, Colorado 80401, USA
Robert Reedy
Affiliation:
National Renewable Energy Laboratory, Golden, Colorado 80401, USA
Paul Stradins
Affiliation:
National Renewable Energy Laboratory, Golden, Colorado 80401, USA
*
a)Address all correspondence to this author. e-mail: [email protected]
Get access

Abstract

We apply n- and p-type polycrystalline silicon (poly-Si) films on tunneling SiOx to form passivated contacts to n-type Si wafers. The resulting induced emitter and n+/n back surface field junctions of high carrier selectivity and low contact resistivity enable high efficiency Si solar cells. This work addresses the materials science of their performance governed by the properties of the individual layers (poly-Si, tunneling oxide) and more importantly, by the process history of the cell as a whole. Tunneling SiOx layers (<2 nm) are grown thermally or chemically, followed by a plasma enhanced chemical vapor deposition growth of p+ or n+ doped a-Si:H. The latter is thermally crystallized into poly-Si, resulting in grain nucleation and growth as well as dopant diffusion within the poly-Si and penetration through the tunneling oxide into the Si base wafer. The cell process is designed to improve the passivation of both oxide interfaces and tunneling transport through the oxide. A novel passivation technique involves coating of the passivated contact and whole cell with atomic layer deposited Al2O3 and activating them at 400 °C. The resulting excellent passivation persists after subsequent chemical removal of the Al2O3. The preceding cell process steps must be carefully tailored to avoid structural and morphological defects, as well as to maintain or improve passivation, and carrier selective transport. Furthermore, passivated contact metallization presents significant challenges, often resulting in passivation loss. Suggested remedies include improved Si cell wafer surface morphology (without micropyramids) and postdeposited a-Si:H capping layers over the poly-Si.

Keywords

photovoltaicpassivationthin film
Type
Invited Feature Paper
Information
Journal of Materials Research , Volume 31 , Issue 6 , 28 March 2016 , pp. 671 - 681
Copyright
Copyright © Materials Research Society 2016 

Access options

Get access to the full version of this content by using one of the access options below. (Log in options will check for institutional or personal access. Content may require purchase if you do not have access.)

References

REFERENCES

Van Halen, P. and Pulfrey, D.: High-gain bipolar transistors with polysilicon tunnel junction emitter contacts. IEEE Trans. Electron Devices 32(7), 1307 (1985).Google Scholar
Green, M., Gusev, E., Degraeve, R., and Garfunkel, E.: Ultrathin (<4 nm) SiO2 and Si–O–N gate dielectric layers for silicon microelectronics: Understanding the processing, structure, and physical and electrical limits. J. Appl. Phys. 90(5), 2057 (2001).CrossRefGoogle Scholar
Gan, J.: Polysilicon emitters for silicon concentrator solar cells. Ph.D. Thesis, Stanford University, Stanford, 1990.Google Scholar
Post, I., Ashburn, P., and Wolstenholme, G.: Polysilicon emitters for bipolar transistors: A review and re-evaluation of theory and experiment. IEEE Trans. Electron Devices 39(7), 1717 (1992).Google Scholar
Glunz, S.W., Feldmann, F., Richter, A., Bivour, M., Reichel, C., Steinkemper, H., Benick, J., and Hermle, M.: The irresistible charm of a simple current flow pattern—25% with a solar cell featuring a full-area back contact. In Proc. 32nd EU PVSEC (Hamburg, Germany, 2015).Google Scholar
Asuha, H.K., Maida, O., Takahashi, M., and Iwasa, H.: Nitric acid oxidation of Si to form ultrathin silicon dioxide layers with a low leakage current density. J. Appl. Phys. 94(11), 7328 (2003).Google Scholar
van der Meulen, Y.J.: Kinetics of thermal growth of ultra-thin layers of SiO2 on silicon. I. Experiment. J. Electrochem. Soc. 119(4), 530 (1972).CrossRefGoogle Scholar
Fehlner, F.P.: Formation of ultrathin oxide films on silicon. J. Electrochem. Soc. 119(12), 1723 (1972).Google Scholar
Dingemans, G. and Kessels, W.M.M.: Status and prospects of Al2O3-based surface passivation schemes for silicon solar cells. J. Vac. Sci.Technol. A 30(4), 040802 (2012).CrossRefGoogle Scholar
Stradins, P., Essig, S., Nemeth, W., Lee, B.G., Young, D., Norman, A., Liu, Y., Luo, J.W., Warren, E., Dameron, A., and LaSalvia, V.: Passivated tunneling contacts to n-type wafer silicon and their Implementation into high performance solar cells. In Proc. 6th WCPEC (Kyoto, Japan, 2014).Google Scholar
Nemeth, W., LaSalvia, V., Page, M.R., Warren, E., Dameron, A., Norman, A., Lee, B.G., Young, D., and Stradins, P.: Implementation of tunneling passivated contacts into industrially relevant n-Cz Si solar cells. In Proc. 42nd IEEE PVSC (IEEE: New Orleans, 2015).Google Scholar
Minamisawa, R., Papadopoulos, C., Jabrany, R., Knoll, L., Corvasce, C., and Rahimo, M.: Formation of insulated-gate bipolar transistor highly activated anodes via nickel silicidation with dopant segregation. IEEE Electron. Device Lett. 36(5), 487 (2015).CrossRefGoogle Scholar
Akazawa, H.: Delta-doping of boron atoms by photoexcited chemical vapor deposition. J. Vac. Sci. Technol. A 30(2), 021504 (2012).Google Scholar
Fair, R.: Physical models of boron diffusion in ultrathin gate oxides. J. Electrochem. Soc. 144(2), 708 (1997).Google Scholar
Reed, M. and Plummer, J.: Chemistry of Si-SiO2 interface trap annealing. J. Appl. Phys. 63(12), 5776 (1998).CrossRefGoogle Scholar
Pollack, G., Richardson, W., Malhi, S., Bonifield, T., Shichijo, H., Banerjee, S., Elahy, M., Shah, A., Womack, R., and Chatterjee, P.: Hydrogen passivation of polysilicon MOSFET's from a plasma nitride source. IEEE Electron Device Lett. 5, 468 (1984).Google Scholar
Ok, Y., Upadhyaya, A., Rounsaville, B., Madini, K., Jones, K., Ryu, K., Chandrasekaran, V., Das, A., McPherson, B., Gupta, A., and Rohatgi, A.: High implied Voc (>715 mV) and low emitter saturation current density (∼10 fA/cm2) from a lightly B doped implanted emitter. In Proc. 42nd IEEE PVSC (IEEE: New Orleans, 2015).Google Scholar
Lindekugel, S., Lautenschlager, H., Ruof, T., and Reber, S.: Plasma hydrogen passivation for crystalline silicon thin-films. In Proc. 23rd EU-PVSEC (Valencia, Spain, 2008).Google Scholar
Dingemans, G., Beyer, W., Van de Sanden, M.C.M., and Kessels, W.M.M.: Hydrogen induced passivation of Si interfaces by Al2O3 films and SiO2/Al2O3 stacks. Appl. Phys. Lett. 97, 152106 (2010).Google Scholar
Mihailetchi, V., Komatsu, Y., and Geerligs, L.: Nitric acid pretreatment for the passivation of boron emitters for n-type base silicon solar cells. Appl. Phys. Lett. 92(6), 63510 (2008).Google Scholar
Mack, S., Wolf, A., Brosinsky, C., Schmeisser, S., Kimmerle, A., Saint-Cast, P., Hofmann, M., and Biro, D.: Silicon surface passivation by thin thermal oxide/PECVD layer stack systems. IEEE J. Photovoltaics 1(2), 135 (2011).Google Scholar
Brotherton, S.: Polycrystalline silicon thin film transistors. Semicond. Sci. Technol. 10, 721 (1995).Google Scholar
Young, D., Nemeth, W., LaSalvia, V., Reedy, R., Essig, S., Bateman, N., and Stradins, P.: Interdigitated back passivated contact (IBPC) solar cells formed by ion implantation. IEEE J. Photovoltaics 6(1), 41 (2016).Google Scholar
Abbasi, S.A. and Brunnschweiler, A.: Effects of masking oxide on diffusion into silicon. IEEE Proc. Solid-State Electron Devices 128(5), 185 (1981).Google Scholar
Shao, L., Liu, J., Chen, Q.Y., and Chu, W.K.: Boron diffusion in silicon: The anomalies and control by point defect engineering. Mater. Sci. Eng., R 42(3), 65 (2003).Google Scholar
Batra, S., Manning, M., Dennison, C., Sultan, A., Bhattacharya, S., Banerjee, S., Lobo, M., Lux, G., Kirschbaum, C., Norberg, J., Smith, T., and Mulvaney, B.: Discontinuity of B-diffusion profiles at the interface of polycrystalline Si and single crystal Si. J. Appl. Phys. 73(8), 3800 (1993).Google Scholar
Kurachi, I. and Yoshioka, K.: Enhancement and retardation of thermal boron diffusion in silicon from atmospheric pressure chemical vapor deposited boron silicate glass film. Jpn. J. Appl. Phys. 53(3), 036504 (2014).Google Scholar
Chen, T., Lei, T., Lin, H., Chang, C., Hsieh, W., and Chen, L.: Low temperature growth of silicon-boron layer by ultrahigh vacuum chemical vapor deposition. Appl. Phys. Lett. 64(14), 1853 (1994).Google Scholar
Kanaki, A., Zianni, X., and Narducci, D.: Boron diffusion in silicon in the presence of grain boundaries and voids. Mater. Today Proc. 2.2, 583 (2015).Google Scholar
Street, R.A.: Hydrogenated Amorphous Silicon (Cambridge University Press, Cambridge, England, 1991); p. 51.CrossRefGoogle Scholar
Campbell, S., Cooper, K., Dixon, L., Earwaker, R., Port, S., and Schiffrin, D.: Inhibition of pyramid formation in the etching of Si p (100) in aqueous potassium hydroxide-isopropanol. J. Micromech. Microeng. 5(3), 209 (1995).CrossRefGoogle Scholar
Auret, F.D. and Mooney, P.M.: Deep levels introduced during electron-beam deposition of metals on n-type silicon. J. Appl. Phys. 55(4), 988 (1984).Google Scholar
Kuwano, K. and Ashok, S.: Investigation of sputtered indium-tin oxide/silicon interfaces: Ion damage, hydrogen passivation and low-temperature anneal. Appl. Surf. Sci. 117, 629 (1997).CrossRefGoogle Scholar