Surface and bulk passivation of multicrystalline silicon solar cells by ...

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61 recombination in the SCR influences the magnitude of Seff, whereas, at high injection levels, Seff is mostly determined by the recombination at the surface. After plasma deposition, there is damage beneath the Si surface up to about 20 nm deep [97, 98], which agrees well with the calculated L. Note that the major amount of surface damage can be healed by the RTA process so that the width of the SCR will subsequently be reduced. Therefore, a reduction of minority-carrier recombination in the SCR is expected after the firing step for metallization of Si solar cells. 3.3 H Transportation Mediated by SiΝ :Η Layer Based on the damaged layer and trapping/detrapping theory, a semi-quantitative hydrogen transportation model is proposed which can be simply described in the following steps: (i) A large amount of the hydrogen atoms are trapped and "stored" in processinduced traps (PITS) across the damaged region produced by the plasma process during the nitride deposition. (ii) In a rapid thermal annealing (RTA) step, H is released from the surface and redistributed into the bulk region. Also, because the concentration of H in the damaged region is higher than that in the SίΝx :H layer, some of the H may migrate into the nitride layer. (iii) H evolution from SiΝ :H layer thus occurs both ways: into the air and into Si. The diffusion process of H into the bulk region and the out-diffusion into the ambient occur simultaneously. As the H diffuses deeper into Si, it saturates the traps and other defects, requiring less H for passivation. At the same time, the damage at the surface is
62 being healed. Eventually, all the traps in the bulk of the Si are filled with H, the surface damage is healed and the H transport mediated by SiΝ :H reaches a steady state. Outflow of H across the SiΝ :H/Si interface stops accordingly [97]. An illustration of hydrogen transport is shown in Figure 3.13. Figure 3.13 A schematic illustration of H transport from SiΝ :H layer to bulk Si (the black dots represent H atoms, and the brown dots represent defects/impurities in the bulk Si).
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Copyright Warning & Restrictions Th
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ABSTRACT SURFACE AND BULK PASSIVATI
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SURFACE AND BULK PASSIVATION OF MUL
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APPROVAL PAGE SURFACE AND BULK PASS
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Chuan Li, B.L. Sopori, P. Rupnowski
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ACKNOWLEDGEMENT The work presented
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TABLE OF CONTENTS (Continued) Chapt
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LIST OF TABLES Table Page 2.1 Posit
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LIST OF FIGURES (Continued) Figure
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LIST OF FIGURES (Continued) Figure
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2 percent; however, soon, more adva
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4 Figure 1.1 World solar module pro
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6 bond is called a hole. It too can
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8 Figure 1.4 The I-V characteristic
Page 29 and 30: 10 First generation cells consist o
Page 31 and 32: 12 Basically, materials for manufac
Page 33 and 34: 14 Defects are generally categorize
Page 35 and 36: 16 copper, or nickel in concentrati
Page 37 and 38: 18 the SiNx:H layer during the ther
Page 39 and 40: CHAPTER 2 SILICON NITRIDE LAYER FOR
Page 41 and 42: 22 reflectance of polished Si can b
Page 43 and 44: 24 information is application-orien
Page 45 and 46: 26 film fed growth (EFG) ribbon sil
Page 47 and 48: 28 Figure 2.5 Deposition of SiΝ :
Page 49 and 50: 30 Figure 2.6 shows the dependence
Page 51 and 52: 32 atoms, the interface states are
Page 53 and 54: 34 2.5 Bulk Passivation of Si by Si
Page 55 and 56: 36 It was found that the bulk lifet
Page 57 and 58: CHAPTER 3 MODELING OF SURFACE RECOM
Page 59 and 60: 40 Figure 3.2 Schematic diagram of
Page 61 and 62: 42 σ and σp are the capture cross
Page 63 and 64: 44 Qsi — charge density induced i
Page 66 and 67: 47 Figure 3.5 The calculated depend
Page 68 and 69: 49 * 10 Λ m; m is in a range from
Page 70 and 71: 51 Na, sigma_n, sigma_p: enter x.xx
Page 72 and 73: 53 Figure 3.7 Measured Seff(Δn) de
Page 74 and 75: 55 curves converge to a single valu
Page 76 and 77: 57 seen that, initially Ss decrease
Page 78 and 79: 59 carrier recombination within the
Page 82 and 83: 63 Figure 3.13 shows that: 1) after
Page 84 and 85: CHAPTER 4 MINORITY-CARRIER LIFETIME
Page 86 and 87: 67 Figure 4.1 Α photograph of QSSP
Page 88 and 89: 69 work. The most convenient is 1 m
Page 90 and 91: 7Ι dependence of the minority carr
Page 92 and 93: 73 It was tempting to assume that l
Page 94 and 95: 75 resistivities and lifetime) do n
Page 96 and 97: 77 5.2 Objective An electronic mode
Page 98 and 99: 79 Figure 5.2 is a photograph of a
Page 100 and 101: 81 impurity-gettering methods which
Page 102 and 103: 83 distribution of local currents a
Page 104 and 105: 85 modeling. Wafers were selected f
Page 106 and 107: 87 Figure 5.5 A comparison of (a) d
Page 108 and 109: 89 alloying results in metallizatio
Page 110 and 111: 91 (i) Defect clusters are the prim
Page 112 and 113: 93 SiNX induced charge density on t
Page 114 and 115: APPENDIX I PROGRAMS TO CALCULATE SR
Page 116 and 117: 97 phin = -ΕΙ - 1 / beta * log(nd
Page 118 and 119: 99 ίter3 = 0 for xi=1 to nmax/2-1
Page 120 and 121: 101 input "output file name {XXXXXX
Page 122 and 123: 103 F (i) = (exp (beta * (phip - ph
Page 124 and 125: APPENDIX III COMPUTATIONAL METHOD F
Page 126 and 127: 107 where, dscr is the width of the
Page 128 and 129: REFERENCES 1. E. Becquerel , C. R.
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44. L.L. Alt, S.W. Ing. Jr. and K.W
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90. B.L. Sopori, Y. Zhang, and N.M.
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