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

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67 Figure 4.1 Α photograph of QSSPCD apparatus at NREL. 4.2 Wafer Preparation and Passivation Procedure for Producible Minority Carrier Lifetime Measurements 4.2.1 Objective Measurement of the bulk minority carrier lifetime (Tb) by QSSPCD is strongly influenced by surface recombination. Α number of techniques are known to lower the effective surface recombination velocity. These include use of oxidation, floating Ν/Ρ junction, SiΝ X:H layer, HF immersion, and use of iodine in ethanol or methanol (Ι-Ε or I-Μ solution) [ 101-107]. Use of I-Ε (or I-M) solution appears to be very simple and this technique does not require any high temperature treatment such as oxidation, diffusion, or nitridation processes that can change Tb [101].Yet, this is not a preferred procedure within the photovoltaic community because it is a common experience that it is difficult to
obtain same τb-values reproducibly, particularly when the silicon wafer lifetime is long. The objective for studying lifetime measurements using I-Ε passivation is twofold: (i) to apply it to compare lifetimes of wafers (having different 'Lb) by various techniques such as QSSPCD and transient PCD using short laser pulses of different light intensity; (ii) to make minority-carrier diffusion length (L) measurements by surface photovoltage (SPV) technique, and to use τb and L data to determine diffusivity (D) values for various impurity and defect concentrations, using the relationship L =√Dτ b [103,106,107] There are various reasons which can make lifetime measurements irreproducible using I-Ε solution passivation, such as the influence of the strength of iodine in ethanol solution, wafer cleaning procedures, influence of wafer container during lifetime measurements, and stability of the I-Ε solution. Although some of these studies were also performed by other researchers, they only examined individual parameters [102]. The objective of this study was to examine interdependencies between these parameters. 4.2.2 Influence of Wafer Cleaning The initial cleaning procedure ("ICP") in this study was similar to those used by others, and consisted of the following: removal of organics by solvent clean followed by DI water rinse, piranha (H2SO4:Η2O2 2:1) clean at 80°C, dilute HF rinse, DI water rinse and nitrogen drying. Following this cleaning by "ICP", the sample was placed in a Petri dish or polyethylene bag. It was found that zip-lock bags provided an excellent way to passivate the samples. A variety of bags of different quality and thicknesses were utilized in this
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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
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 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 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.
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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