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

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81 impurity-gettering methods which must dissolve the precipitates during a gettering process. 5.4 Influence of Defect Clusters on Solar Cell Performance Defect clusters constitute regions of high carrier recombination resulting in low photocurrent generation, which can be easily observed by performing light beam induced current (LBIC) mapping. However, their dominant effect occurs through a voltage-degradation mechanism. Defect cluster regions develop a lower voltage compared to defect-free regions during the cell operation. Because the entire cell is connected through a common junction, the defect cluster regions exert a shunting influence on the entire cell. Unfortunately, the shunting behavior of the defect clusters cannot be evaluated through experimental measurements alone. It requires a combination of theoretical modeling to include the distributed nature of the cell and experimental measurements pertaining to local characteristics of the cell. The next section briefly describes the use of a network model to evaluate the efficiency loss due to defect clusters. This model was developed previously to describe a nonuniform solar cell. The detailed discussion of original model can be found in the literature [114]. 5.4.1 Theory Α conventional approach in defect modeling for calculating the influence of defects on the material quality is to estimate the "average" carrier recombination and express it in terms of an average minority-carrier lifetime or diffusion length. However, such a procedure will not work for device modeling, because a solar cell is a distributed device in which each region "communicates with" all other regions and the entire device "is sensitive to" the presence of each defect cluster. Hence it is necessary to calculate the
82 characteristics of each local device using its local properties, and then calculate the influence of each local device on the entire device. This approach permits the calculation of the influence of any defect distribution on the total device performance, and can be applied to calculate the performance of the device without any defects, to determine losses introduced by various defect distributions. This formalism can be easily incorporated into the Network Model developed for an inhomogeneous solar cell [114]. The network model builds a large-area solar cell from an array (40x40) of small-area, local cells that are interconnected through a common junction and a bus. Each small-area cell is assigned a defect density corresponding to that in the actual wafer for the corresponding location. Figure 5.4(a) illustrates this model. In the present analysis, a defect cluster is considered as a localized, large defect that propagates through the entire cell (crossing both the base and the emitter regions of the cell), as illustrated in figure 5.4(b). Because of very high recombination and large size, one can ignore internal carrier transport and band bending associated with each defect cluster. The defect region acts as a "poor" device in the spatial distribution of the total cell. The modeling requires two steps. First, each device is represented in terms of the recombination properties associated with its defect density, which yields values of photogenerated current density (J ph), a minority-carrier lifetime (τ), and dark saturation-current components J01 and J02, corresponding to the bulk and the junction recombination, respectively. Next, the diode array is interconnected using resistive components corresponding to the sheet resistance of the junction and the metallization pattern. The network is solved to yield the terminal characteristics of the device, as well as
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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 :
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 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 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.
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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