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

More documents

Recommendations

Info

5 Figure 1.2 A schematic of photogeneration effect. In order to produce a solar cell, the semiconductor has to be contaminated or doped. Pure semiconductors (also called "intrinsic") do not conduct electricity at room temperature and are thus not useful for the fabrication of electronic devices. Semiconductors conduct electricity if they are doped with a small amount of impurity atoms. In the case of silicon (Si), these would be atoms from group III and group V of the periodic table. Impurities in semiconductors are divided into two broad categories: donors and acceptors. A donor is an element with typically one more valence electron than the group IV semiconductor. Each Si atom has four electrons in its outermost shell; these electrons are involved in forming chemical bonds with the neighboring Si atoms. For example, an arsenic (As) atom has five electrons in its outermost shell. The extra electron in As can be easily removed from the As donor on which it was originally localized. If this happens, the electron can move freely in the semiconductor material and conduct electric current. A semiconductor doped with donors is known as n-type material. An acceptor is an element with typically one fewer valence electron than the element that forms the semiconductor. A boron (B) atom has three electrons in its outermost shell. The missing electron in the chemical
6 bond is called a hole. It too can be easily removed from the vicinity of the B atom and move freely in the semiconductor material. A semiconductor doped with acceptors is known as p-type material. As the two types of semiconductors are brought together, a p-n junction is formed and the concentration gradient of carriers near the metallurgical junction leads to a carrier flow. As the junction region gets "depleted" of carriers, the ionized dopant cores left behind build up an electric field across the junction, which introduces drift current that is opposite to the diffusion current. An equilibrium situation will be arrived at as the two currents match. In the dark, the equilibrated p-n junction should have a spatially uniform Fermi level and no net macroscopic current flow is observed. When a p-n junction is illuminated, excess electron-hole pairs are generated by light throughout the cell. This disturbs the equilibrium state of carriers everywhere. The excess electrons (holes) in n-type (p-type) region diffuse towards the junction and are quickly pulled across the depletion region by the electric field. This is the photovoltaic effect. A simplified solar cell model is usually illustrated as a current source in parallel with a diode and, a shunt resistance and a series resistance component as well are added. The resulting equivalent circuit of a solar cell is shown in Figure 1.3. Notice that the current generated by the photons is represented by an independent source. The two resistors shown in Figure 1.3 represent two of the losses in a solar cell. Rs is a series resistance loss due, primarily, to the ohmic loss in the surface of the solar cell. The shunt resistance, Rsh, is used to model leakage currents. A shunt resistance of a few hundred ohms does not reduce the output power of the solar cell appreciably. In reality, Rsh is much larger than a few hundred ohms and can in most
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: 4 Figure 1.1 World solar module pro
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 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.
show all

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

Create successful ePaper yourself

Delete template?

Save as template?