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

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91 (i) Defect clusters are the primary sites of impurity precipitation, and hence are not gettered by conventional gettering treatments of P diffusion and Al alloying. (ii) Defect clusters act as shunts, creating "internal sinks," which dissipate power within the cell. (iii) The loss depends on several factors: the nature of the impurity precipitates, distribution and total area of defects compared to the cell area, quality of the base material (the regions with no defects, in which cell performance is limited by the dissolved impurities only), and cell processing technology. (iv) In a typical cell, the defect clusters produce an efficiency loss of 3 to 4 percent. In order to reduce the influence of defect clusters, techniques for dissolving the precipitates during impurity gettering must be developed. These techniques must be costeffective. Concomitantly, it is of major interest to determine the achievable improvement in the cell efficiency. An intuitive approach to mitigating the influence of defect clusters would be to dissolve the precipitates by a high-temperature treatment prior to, or during gettering. A new approach to dissolution of impurity precipitates has recently been developed at NREL, which uses vacancy injection to lower the temperature needed for precipitate dissolution.
CHAPTER 6 CONCLUSIONS AND FUTURE DIRECTIONS 6.1 Conclusions Extended Shockley-Reed-Hall (SRH) calculations across the space charge region was applied to evaluate recombination effects in the SiΝx :H-Si interface. Modeling results show that the overall recombination that is occurring at this interface should consider the charge-induced electric fields both at the edge of and across the space charge region. This is especially required in order to explain the injection-level dependence of the effective surface (interface) recombination velocity (Self). Previous extended SRH modeling results successfully addressed the surface (interface) recombination mechanism at the SiO 2-Si interface. Low Seff of the PECVD SiO2-passivated Si surface is attributed to a combination of moderately low density of interface states at midgap [Dit = (1-10) x 10 10 cm 2 eV-1] and a high positive oxide charge density [QOX = (1-10) x 10 11 cm2]. The presence of a positive charge leads to a band bending at the SiO2-Si interface and will result in separation of electrons and holes, thus reducing carrier recombination. Similarly, the deposition of SiΝ :H layers on the silicon substrate leads to the formation of a space charge region at the SiΝx :H/Si interface and is characterized by a fixed positive charge density (Qf) of the order of 10 12 cm2. In p-type Si, a depletion/inversion layer is formed, while in n-type Si, the positively charged insulator attracts majority carriers and repels minority carriers. Hence, an accumulation layer is formed. However, according to this model calculation, very high Qf (1-3 x 10 12 cm2), for 92
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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
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10 First generation cells consist o
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12 Basically, materials for manufac
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14 Defects are generally categorize
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16 copper, or nickel in concentrati
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18 the SiNx:H layer during the ther
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CHAPTER 2 SILICON NITRIDE LAYER FOR
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22 reflectance of polished Si can b
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24 information is application-orien
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26 film fed growth (EFG) ribbon sil
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28 Figure 2.5 Deposition of SiΝ :
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30 Figure 2.6 shows the dependence
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32 atoms, the interface states are
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34 2.5 Bulk Passivation of Si by Si
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36 It was found that the bulk lifet
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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 80 and 81: 61 recombination in the SCR influen
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 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.
Page 130 and 131: 44. L.L. Alt, S.W. Ing. Jr. and K.W
Page 132 and 133: 90. B.L. Sopori, Y. Zhang, and N.M.
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