Plasma enhanced chemical vapor deposition of excellent a-Si:H passivation layers for a-Si:H/c-Si heterojunction solar cells at high pressure and high power

Abstract

The intrinsic a-Si:H passivation layer inserted between the doped a-Si:H layer and the c-Si substrate is very crucial for improving the performance of the a-Si:H/c-Si heterojunction (SHJ) solar cell. The passivation performance of the a-Si:H layer is strongly dependent on its microstructure. Usually, the compact a-Si:H deposited near the transition from the amorphous phase to the nanocrystalline phase by plasma enhanced chemical vapor deposition (PECVD) can provide excellent passivation. However, at the low deposition pressure and low deposition power, such an a-Si:H layer can be only prepared in a narrow region. The deposition condition must be controlled very carefully. In this paper, intrinsic a-Si:H layers were prepared on n-type Cz c-Si substrates by 27.12 MHz PECVD at a high deposition pressure and high deposition power. The corresponding passivation performance on c-Si was investigated by minority carrier lifetime measurement. It was found that an excellent a-Si:H passivation layer could be obtained in a very wide deposition pressure and power region. Such wide process window would be very beneficial for improving the uniformity and the yield for the solar cell fabrication. The a-Si:H layer microstructure was further investigated by Raman and Fourier transform infrared (FTIR) spectroscopy characterization. The correlation between the microstructure and the passivation performance was revealed. According to the above findings, the a-Si:H passivation performance was optimized more elaborately. Finally, a large-area SHJ solar cell with an efficiency of 22.25% was fabricated on the commercial 156 mm pseudo-square n-type Cz c-Si substrate with the open-circuit voltage (V_oc) of up to 0.732 V.

Key words： PECVD; high pressure and high power; a-Si:H microstructure; passivation; heterojunction solar cell

Acknowledgments

This work was supported by the National High Technology Research and Development Program of China (863 Program) (Grant No. 2011AA050502) and the National Natural Science Foundation of China (Grant No. 61274061).

References

1 Taguchi M, Tanaka M, Matsuyama T, Matsuoka T, Tsuda S, Nakano S, Kishi Y, Kuwano Y. Improvement of the conversion efficiency of polycrystalline silicon thin film solar cell. In: Proceedings of Technical Digest of the 5th International Photovoltaic Science and Engineering Conference. Kyoto, Japan, 1990: 689–692

2 Scherg-Kurmes H, Körner S, Ring S, Klaus M, Korte L, Ruske F, Schlatmann R, Rech B, Szyszka B. High mobility In₂O₃:H as contact layer for a-Si:H/c-Si heterojunction and c-Si:H thin film solar cells. Thin Solid Films, 2015, 594: 316–322

3 Taguchi M, Yano A, Tohoda S, Matsuyama K, Nakamura Y, Nishiwaki T, Fujita K, Maruyama E. 24.7% record efficiency HIT solar cell on thin silicon wafer. IEEE Journal of Photovoltaics, 2014, 4(1): 96–99

4 de Wolf S, Descoeudres A, Holman Z C, Ballif C. High-efficiency silicon heterojunction solar cells: a review. Green, 2012, 2(1): 7– 24

5 Schulze T F, Korte L, Rech B. Impact of a-Si:H hydrogen depth profiles on passivation properties in a-Si:H/c-Si heterojunctions. Thin Solid Films, 2012, 520(13): 4439–4444

6 Wang Q, Page M R, Iwaniczko E, Xu Y Q, Roybal L, Bauer R, To B, Yuan H C, Duda A, Hasoon F, Yan Y F, Levi D, Meier D, Branz H M, Wang T H. Efficient heterojunction solar cells on p-type crystal silicon wafers. Applied Physics Letters, 2010, 96(1): 013507

7 Fesquet L, Olibet S, Vallat-Sauvain E, Shah A, Ballif C. High quality surface passivation and heterojunction fabrication by VHF-PECVD deposition of amorphous silicon on crystalline Si: theory and experiments. In: Proceedings of 23rd European Photovoltaic Solar Energy Conference and Exhibition. Valencia, Spain, 2008, 2: 2DV 2.14

8 Fujiwara H, Kaneko T, Kondo M. Optimization of interface structures in crystalline silicon heterojunction solar cells. Solar Energy Materials and Solar Cells, 2009, 93(6-7): 725–728

9 Kim S K, Lee J C, Park S J, Kim Y J, Yoon K H. Effect of hydrogen dilution on intrinsic a-Si:H layer between emitter and Si wafer in silicon heterojunction solar cell. Solar Energy Materials and Solar Cells, 2008, 92(3): 298–301

10 Kim S, Dao V A, Shin C, Cho J, Lee Y, Balaji N, Ahn S, Kim Y, Yi J. Low defect interface study of intrinsic layer for c-Si surface passivation in a-Si:H/c-Si heterojunction solar cells. Thin Solid Films, 2012, 521: 45–49

11 Lee S J, Kim S H, Kim D W, Kim K H, Kim B K, Jang J. Effect of hydrogen plasma passivation on performance of HIT solar cells. Solar Energy Materials and Solar Cells, 2011, 95(1): 81–83

12 Zhao L, Diao H W, Zeng X B, Zhou C L, Li H L, Wang W J. Comparative study of the surface passivation on crystalline silicon by silicon thin films with different structures. Physica B: Condensed Matter, 2010, 405(1): 61–64

13 Meddeb H, Bearda T, Abdelraheem Y, Ezzaouia H, Gordon I, Szlufcik J, Poortmans J. Structural, hydrogen bonding and in situ studies of the effect of hydrogen dilution on the passivation by amorphous silicon of n-type crystalline (100) silicon surfaces. Journal of Physics D: Applied Physics, 2015, 48(41): 415301

14 Zhang L P, Liu W Z, Guo W W, Bao J, Zhang X Y, Liu J N, Wang D L, Meng F Y, Liu Z X. Interface processing of amorphous-crystalline silicon heterojunction prior to the formation of amorphous-to-nanocrystalline transition phase. IEEE Journal of Photovoltaics, 2016, 6(3): 604–610

15 Ge J, Ling Z P, Wong J, Stangl R, Aberle A G, Mueller T. Analysis of intrinsic hydrogenated amorphous silicon passivation layer growth for use in heterojunction silicon wafer solar cells by optical emission spectroscopy. Journal of Applied Physics, 2013, 113(23): 234310

16 Guo W W, Zhang L P, Bao J, Meng F Y, Liu J N, Wang D L, Bian J Y, Liu W Z, Feng Z Q, Verlinden P J, Liu Z X. Defining a parameter of plasma-enhanced CVD to characterize the effect of silicon-surface passivation in heterojunction solar cells. Japanese Journal of Applied Physics, 2015, 54(4): 041402

17 Geissbühler J, De Wolf S, Demaurex B, Seif J P, Alexander D T L, Barraud L, Ballif C. Amorphous/crystalline silicon interface defects induced by hydrogen plasma treatments. Applied Physics Letters, 2013, 102(23): 231604

18 Deligiannis D, Marioleas V, Vasudevan R, Visser C C G, van Swaaij R A C M M, Zeman M. Understanding the thickness-dependent effective lifetime of crystalline silicon passivated with a thin layer of intrinsic hydrogenated amorphous silicon using a nanometer-accurate wet-etching method. Journal of Applied Physics, 2016, 119(23): 235307

19 De Wolf S. Intrinsic and doped a-Si:H/c-Si interface passivation. In: Physics and Technology of Amorphous-crystalline Heterostructure Silicon Solar Cells. Berlin: Springer-Verlag Berlin Heidelberg, 2012: 223–259<?Pub Caret?>

20 Sproul A B. Dimensionless solution of the equation describing the effect of surface recombination on carrier decay in semiconductors. Journal of Applied Physics, 1994, 76(5): 2851–2854

21 Beeman D, Tsu R, Thorpe M F. Structural information from the Raman spectrum of amorphous silicon. Physical Review B: Condensed Matter and Materials Physics, 1985, 32(2): 874–878

22 Morell G, Katiyar R S, Weisz S Z, Jia H, Shinar J, Balberg I. Raman study of the network disorder in sputtered and glow discharge a-Si:H films. Journal of Applied Physics, 1995, 78(8): 5120–5125

23 Ouwens J D, Schropp R E I. Hydrogen microstructure in hydrogenated amorphous silicon. Physical Review B: Condensed Matter and Materials Physics, 1996, 54(24): 17759–17762

24 Guo W W, Zhang L P, Meng F Y, Bao J, Wang D L, Liu J N, Feng Z Q, Verlinden P J, Liu Z X. Study of the correlation between hydrogenated amorphous silicon microstructure and crystalline silicon surface passivation in heterojunction solar cells. Physica Status Solidi A: Applications and Materials Science, 2015, 212(10): 2233–2238

25 Langford A A, Fleet M L, Nelson B P, Lanford W A, Maley N. Infrared absorption strength and hydrogen content of hydrogenated amorphous silicon. Physical Review B: Condensed Matter and Materials Physics, 1992, 45(23): 13367–13377