Surface and bulk passivation of multicrystalline silicon solar cells by ...
Surface and bulk passivation of multicrystalline silicon solar cells by ... Surface and bulk passivation of multicrystalline silicon solar cells by ...
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
9<br />
between radiation <strong>and</strong> generation, one finds that recombination cannot be reduced<br />
below its radiative component, yielding a lower basic limit for Vic .<br />
Considering that FF is calculated as a function <strong>of</strong> Vic <strong>by</strong> assuming that the I- V<br />
characteristics <strong>of</strong> a diode are, in an ideal case, an exponential function, calculations<br />
show that FF is limited <strong>by</strong> Egap.<br />
The optimum value <strong>of</strong> Egap for the total energy conversion efficiency<br />
(including charge separation) is 4.5 eV, with a "limited" efficiency approaching<br />
30%. Gallium arsenide (GaAs), indium phosphide (InP), <strong>and</strong> cadmium telluride<br />
(CdTe) are semiconductor materials that have b<strong>and</strong>gap energies very near the<br />
optimum value. However, the first two are too costly for large-scale terrestrial<br />
applications, <strong>and</strong> CdTe has toxicity problems. With crystalline <strong>silicon</strong>, laboratory<br />
<strong>cells</strong> have been produced that are near the corresponding efficiency "limit" <strong>of</strong> 29%-<br />
30% [18, 19]. However, such record <strong>cells</strong> are based on sophisticated designs <strong>and</strong> are<br />
not suited for large-scale commercial utilization. Unlike the small-size, expensive<br />
laboratory facilities, various additional losses must be considered for commercial PV-<br />
Si <strong>cells</strong> <strong>and</strong> compromises between performance <strong>and</strong> cost <strong>of</strong>ten end up with module<br />
efficiencies that are, in the best cases, 15% — 20% [20].<br />
1.3 Silicon Solar Cells<br />
1.3.1 Three Generations <strong>of</strong> Solar Cells<br />
Solar <strong>cells</strong> can be conveniently classified into three generations regarding their<br />
history, research <strong>and</strong> applications, even though, in reality, these generations are<br />
concurrently present in commercial production [21].
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