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

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39 Figure 3.1 Band-to band recombination in a direct band-gap semiconductor [76]. Band-to-band transition is typically also a radiative transition in direct-bandgap semiconductors such as GaAs and is technically exploited in light-emitting diodes (LEDs). 3.1.1.2 Trap-Assisted Recombination. Trap-assisted recombination occurs when an electron falls into a "trap" — i.e., an energy level within the bandgap caused by the presence of a foreign atom or a structural defect. Once the trap is filled, it cannot accept another electron. The electron occupying the trap, in a second step, moves into an empty valence band state, thereby completing the recombination process. One can envision this process as a two-step transition of an electron from the conduction band to the valence band or as the annihilation of the electron and hole, which meet each other in the trap. This process is often referred to as Shockley-Read-Hall (SRH) recombination [77, 78]. Figure 3.2 shows the forbidden gap of a semiconductor that has several types of impurity levels. Those near the midgap position, Ε, are labeled as recombination centers. Also shown are levels that are designated as electron traps and hole traps. These lie near the conduction band and the valence band, respectively.
40 Figure 3.2 Schematic diagram of impurity-related energy levels within the forbidden gap of a semiconductor. Levels are labeled as to whether the defect is likely to be a trap or a recombination center according to the SRH model. 3.1.1.3 Auger Recombination. Auger recombination is a process in which an electron and a hole recombine in a band-to-band transition, but now the resulting energy is given off to another electron or hole instead of emitting a photon. Hence, this recombination process involves three charge carriers. The third excited carrier returns to its initial energy state by emitting phonons. 3.1.2 Surface Recombination 3.1.2.1 Fundamentals. Recombination at surfaces and interfaces can have a significant impact on the behavior of semiconductor devices. This is because surfaces and interfaces typically contain a large number of recombination centers. These centers are due to the abrupt termination of the semiconductor crystal, which leaves non-saturated (`dangling') bonds resulting in a large density of defects (surface/interface states). In addition, the
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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
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 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: CHAPTER 3 MODELING OF SURFACE RECOM
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
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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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