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

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93 SiNX induced charge density on the Si surface will lead to no injection level dependence of the effective surface recombination velocity, which is in contradiction to experimental results. This discrepancy implies that, perhaps, other recombination mechanisms are missing in the previous SRV modeling. Α modified SRH formalism, which includes the carrier recombination in the damaged region that is caused by ion bombardment onto the Si wafer during PECVD step, was developed in this study to evaluate the recombination at the SiN X :H-Si interface. Modeling results indicate that, at low injection-levels, carrier recombination in this damaged layer can be the dominant mechanism as compared to the surface recombination. The calculated results seem to be in agreement with the experimental results reported by other research groups. It should be noted that the majority of surface damage can be healed by the rapid thermal annealing process. Therefore, less minoritycarrier recombination in the SCR is expected after the firing treatment of Si solar cells. Minority-carrier life measurements, using QSSPCD technique, indicate that the measurements are very sensitive to wafer preparation and surface passivation. Α simple laboratory procedure for wafer preparation was proposed in this study. Α combination of theoretical and experimental study indicates that, in a typical cell, the defect clusters produce an efficiency loss of 3 to 4 percent in efficiency. In order to reduce the influence of defect clusters, techniques for dissolving the precipitates during impurity gettering must be developed. 6.2 Future Directions The future work may consider the following:
94 1. Although the damaged region at the SiΝ X:H-Si was experimentally identified, additional research is needed to: (a) understand the types of defects/traps in this region and (b) the charge distribution which dominates the surface (interface) recombination at low injection levels. Deep level transient spectroscopy (DLTS) is the technique that can lead to quantifying the interface traps. 2. The previous model of SiΝ X:H-Si interface recombination was modified in this work. In order for the recombination in Si solar cells to be studied in detail, a thorough study of the SiΝX Si interface and the N+/P junction is required. 3. More lifetime measurements and surface recombination velocity calculations need to be performed to support the modeling results. 4. Detailed analyses, such as the process of vacancy injection in rapid thermal anneal step, H transport and evolution from the nitride layer to the bulk Si region, etc, are necessary to determine the optimum process for ΡΕCVD-SiΝ X :H-assissted H passivation of Si solar cells.
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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
Page 57 and 58:
CHAPTER 3 MODELING OF SURFACE RECOM
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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 110 and 111: 91 (i) Defect clusters are the prim
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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