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

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25 2.2 Processing of Silicon Nitride Films for Si Solar Cells Currently hydrogen containing silicon nitride (SiΝ :H) layers deposited by plasma enhanced chemical vapor deposition (PECVD) method have been extensively employed as AR coatings for multicrystalline Si solar cells. This is because of its capability to accomplish multiple functions and eliminate several additional process steps that are required in the fabrication of high-efficiency Si solar cells [42]. PECVD is a method of forming a thin solid film on a substrate by reaction of vapor phase chemicals which contain the required constituents. The reactant gases are activated by plasma energy and react on a temperature-controlled surface to form the thin film. The reactive species, energy, rate of chemical supply and substrate temperature largely determine the film properties. The first publication specifically aimed at plasma-enhanced deposition for semiconductor processing appeared in 1963 [44]. Two years later, PECVD technique was invented [45]. This technique was soon utilized in IC technology and, in the mid-1970s, in photovoltaic (PV) technology, when the first PECVD amorphous silicon (a-Si) thin film solar cell was fabricated in RCA Laboratories by Carlson and Wronski in 1976 [46]. In 1981, for the first time, plasma SiN was applied to single-crystalline silicon metalinsulator-semiconductor inversion-layer (MIS-IL) solar cell cells as a promising dielectric [47, 48]. The first commercial cast me-Si solar cell process with SiN AR coating was developed using available commercial equipment [49]. Since then, plasma SiN has been used by several large Si solar cell venders. To name a few, Mobil Solar (now ASE America) incorporated plasma SiN into edge-defined
26 film fed growth (EFG) ribbon silicon solar cells. An overview of the history of the PECVD SiN can be found in the literature [50]. Silicon nitride deposition by PECVD was described by Sterling and Swann in 1965 [51]. For the photovoltaic application, SiΝ X:H film is usually made from a gas mixture of SiΗ4 and ΝΗ3. Silane acts as a source of silicon and hydrogen. Ammonia, in addition to being a source of nitrogen, has a tendency to deposit SiN with a high ratio of incorporated hydrogen. Deposition is performed in a reactor operating at a pressure from a few hundred mTorr to a few Torn Silane and ammonia or nitrogen react in a plasma at temperatures in the range of 200 to 400°C. The kinetic energy of the plasma is used to dissociate the input gas leading to the following species: SiH4+e—*SiΗ, SiΗ 2, SiΗ3, Si, H+e, ΝΗ3+e— ΝΗ2, ΗΝ, N, H+e. The reaction between the nitrogen- and hydrogen-containing species in the plasma results in an amorphous solid deposit commonly denoted as a-SiΝX:Η or simply SiN. The overall deposition reaction is written as: frequency. The deposition rate depends strongly on rf power, gas flow, chamber pressure and
Page 1 and 2: Copyright Warning & Restrictions Th
Page 3 and 4: ABSTRACT SURFACE AND BULK PASSIVATI
Page 5 and 6: SURFACE AND BULK PASSIVATION OF MUL
Page 7 and 8: APPROVAL PAGE SURFACE AND BULK PASS
Page 9 and 10: Chuan Li, B.L. Sopori, P. Rupnowski
Page 11 and 12: ACKNOWLEDGEMENT The work presented
Page 13 and 14: TABLE OF CONTENTS (Continued) Chapt
Page 15 and 16: LIST OF TABLES Table Page 2.1 Posit
Page 17 and 18: LIST OF FIGURES (Continued) Figure
Page 19 and 20: LIST OF FIGURES (Continued) Figure
Page 21 and 22: 2 percent; however, soon, more adva
Page 23 and 24: 4 Figure 1.1 World solar module pro
Page 25 and 26: 6 bond is called a hole. It too can
Page 27 and 28: 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: 24 information is application-orien
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 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.
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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