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

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9 between radiation and generation, one finds that recombination cannot be reduced below its radiative component, yielding a lower basic limit for Vic . Considering that FF is calculated as a function of Vic by assuming that the I- V characteristics of a diode are, in an ideal case, an exponential function, calculations show that FF is limited by Egap. The optimum value of Egap for the total energy conversion efficiency (including charge separation) is 4.5 eV, with a "limited" efficiency approaching 30%. Gallium arsenide (GaAs), indium phosphide (InP), and cadmium telluride (CdTe) are semiconductor materials that have bandgap energies very near the optimum value. However, the first two are too costly for large-scale terrestrial applications, and CdTe has toxicity problems. With crystalline silicon, laboratory cells have been produced that are near the corresponding efficiency "limit" of 29%- 30% [18, 19]. However, such record cells are based on sophisticated designs and are not suited for large-scale commercial utilization. Unlike the small-size, expensive laboratory facilities, various additional losses must be considered for commercial PV- Si cells and compromises between performance and cost often end up with module efficiencies that are, in the best cases, 15% — 20% [20]. 1.3 Silicon Solar Cells 1.3.1 Three Generations of Solar Cells Solar cells can be conveniently classified into three generations regarding their history, research and applications, even though, in reality, these generations are concurrently present in commercial production [21].
10 First generation cells consist of large-area, high quality and single junction devices. First generation technologies involve high energy and labor input which prevents any significant progress in reducing production costs. Single junction silicon devices are approaching the theoretical limiting efficiency under concentrated sunlight [22] and achieve cost parity with fossil fuel energy generation after a payback period of 5-7 years [23]. However, first-generation cells are expensive to produce because of the high costs of purifying, crystallizing and sawing the single silicon wafer. Secondgeneration solar cells are aimed at reducing costs by using thin films of silicon and other compound semiconductors, such as gallium arsenide (GaAs), cadmium telluride (CdTe), copper indium diselenide (CIS) and copper indium gallium selenide (CIGS) mounted on steel, plastic or glass substrates in order to reduce material mass and, therefore, production costs [24]. However, second-generation devices suffer from structural defects that make them less efficient than their single-crystal counterparts, thus making commercialization of these technologies difficult. In 2007, First Solar produced 200 MW of CdTe solar cells making it the fifth largest producer of solar cells in 2007 and the first ever to be in the top ten companies for production of solar cells using second generation technologies alone [25]. Wurth Solar commercialized its CIS technology in 2007 with production capacities of 15 MW [26]. Nanosolar commercialized its CIGS technology in 2007 with a production capacity of 430 MW for 2008 in the United States and Germany [27]. In 2007, the total market share was as follows: 4.7% for CdTe, thin film silicon at 5.2% and CIGS at 0.5% [25]. Third generation technologies are targeting higher conversion efficiencies of up to 30-60% as compared to the poor performance of second generation while retaining low cost materials and manufacturing techniques [21]. The following are the
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: 8 Figure 1.4 The I-V characteristic
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 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
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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
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67 Figure 4.1 Α photograph of QSSP
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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
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75 resistivities and lifetime) do n
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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
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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
Page 112 and 113:
93 SiNX induced charge density on t
Page 114 and 115:
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
Page 124 and 125:
APPENDIX III COMPUTATIONAL METHOD F
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107 where, dscr is the width of the
Page 128 and 129:
REFERENCES 1. E. Becquerel , C. R.
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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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Surface and bulk passivation of multicrystalline silicon solar cells by ...

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