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

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41 surfaces and interfaces are more likely to contain impurities since they are exposed during the device fabrication process. As discussed above, the trap-assisted recombination is described by the SRH theory. In order to calculate the recombination rate, a number of simplifying assumptions are made [79] : (a) no radiative recombination or Auger recombination; (b) the semiconductor is not degenerate; (c) the energy level of the defects does not change with charge condition; (d) the relaxation time of the charge carriers caught by the defect is negligibly small compared to the average time between two emission processes; (e) the defect concentration is very small compared to the doping density; (f) Fermi-Dirac statistics apply; (g) the defects do not interact with each other (i.e., an electron cannot make a transition from one defect level to another). Based on these assumptions, the SRH theory predicts the following recombination rate Ut (unit cm-3/s) for a single -level defect located at an energy Εt [79] : τρ0 = 1/σpvthΝt τnO TnO = 1/σnvthΝt 1 _ 1
42 σ and σp are the capture cross sections of electrons and holes, νth is the thermal velocity of the electron or hole. The electron and hole concentrations are n and p, respectively. Νt is the volume density of deep levels and Εt is the energy level of the traps, τ„ ο and τ ο are the so-called capture time constant of electrons and holes. Typical values for the capture cross sections of bulk defects in silicon are in the range of 10 i2 10' 18 cm2. The recombination rate is proportional to the thermal velocity and the defect concentration. The driving force for this recombination process is the term np-ni2, which describes the deviation of carrier concentration from the thermal equilibrium values. The SRH recombination rate has been derived in most semiconductor textbooks (Grove and Fitzgerald, 1966; Sze, 1981) and is shown to be [80, 81]: For a doped semiconductor, one has either n0»ρ0 (n-type) or ρo»no (p-type). First, taking the case of an n-type material, one can derive the recombination rate for holes at a single energy level, Ε1, in the forbidden gap. This case is completely symmetrical to that of electron recombination in p-type material. In this expression, n o = ND and p0'0. Therefore, where, p is injection level.
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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
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 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: 40 Figure 3.2 Schematic diagram of
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
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91 (i) Defect clusters are the prim
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93 SiNX induced charge density on t
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APPENDIX I PROGRAMS TO CALCULATE SR
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97 phin = -ΕΙ - 1 / beta * log(nd
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99 ίter3 = 0 for xi=1 to nmax/2-1
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101 input "output file name {XXXXXX
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103 F (i) = (exp (beta * (phip - ph
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APPENDIX III COMPUTATIONAL METHOD F
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107 where, dscr is the width of the
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REFERENCES 1. E. Becquerel , C. R.
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44. L.L. Alt, S.W. Ing. Jr. and K.W
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90. B.L. Sopori, Y. Zhang, and N.M.
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