We succeed in introducing optimum window layer material to fabricate a-Si:H solar cells. The solar cells of window layer which used high energy band gap material would improve Voc and conversion efficiency. The window layer of a-SiO which is a kind of high energy band gap material is effective in obtaining high Voc. The maximum efficiency obtained so far is 5.75%.
In addition, we have shown that deposition pressure plays a key role in determining Jsc of μc-Si:H solar cells fabricated using high deposition rate plasma process. High pressure deposition at 8Torr is effective in obtaining high Jsc. The maximum efficiency obtained so far is 5.045%. We propose that low oxygen concentration behavior associated with the microstructure of high pressure grown μc-Si:H is responsible for the excellent charge collection behavior in p-i-n junction solar cells. Otherwise, we also succeed in utilizing a method technology of DLCP to extract number of detects from intrinsic layer for thin film solar cells. High deposition pressure is effective in suppressing number of detects in the vicinity of p/i interface.
27
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Figure
Figure 2.1(a) The type of superstrate solar cells structure
Figure 2.1(b) The type of substrate solar cells structure
33
Figure 2.2 The current-voltage (I-V) characteristics of thin film solar cells under illumination
Figure 2.3-1 Band diagram of p-i-n junction
34
Figure 2.3-2 Variation of junction capacitance with alternation voltage drive level
Figure 2.3-3 Drive level charge density versus depletion width in the solar cell
35
Figure 3.1 shows current-voltage characteristics of amorphous silicon thin film solar cells under standard illumination conditions
-0.4 -0.2 0.0 0.2 0.4 0.6 0.8 1.0
-15 -10 -5 0 5 10 15
Current density (mA/cm2 )
Voltage (V) P_uc-Si
P_SiC P_SiO
36
Figure 3.2(a) Capacitance vs. dc bias for μc-Si window layer of solar cell. The measuring frequency is 100Hz and the temperature is 300K.The amplitude of the alternating voltage is 25mV、50 mV、75 mV、100 mV, respectively
Depletion width (um)
Figure 3.2(b) Drive level charge density versus depletion width in the solar cell depicted in Figure 3.2(a)
37
Figure 3.3(a) Capacitance vs. dc bias for a-SiC window layer of solar cell. The measuring frequency is 100Hz and the temperature is 300K.The amplitude of the alternating voltage is 25mV、50 mV、75 mV、100 mV, respectively
Depletion width (um)
Figure 3.3(b) Drive level charge density versus depletion width in the solar cell depicted in Figure 3.3(a)
38
Figure 3.4(a) Capacitance vs. dc bias for a-SiO window layer of solar cell. The measuring frequency is 100Hz and the temperature is 300K.The amplitude of the alternating voltage is 25mV、50 mV、75 mV、100 mV, respectively
Depletion width (um)
Figure 3.4(b) Drive level charge density versus depletion width in the solar cell depicted in Figure 3.4(a)
39
Depletion width (um)
0.0 0.1 0.2 0.3 0.4 0.5 0.6
NDL (cm-3 )
0 2e+20 4e+20 6e+20 8e+20 1e+21
uc-Si a-SiC
Figure 3.5 Drive level charge density as a function of depletion width of two different types of a-Si solar cells (see text)
Depletion width (um)
0.0 0.1 0.2 0.3 0.4 0.5 0.6
NDL (cm-3 )
0 2e+20 4e+20 6e+20 8e+20 1e+21
a-SiC a-SiO
Figure 3.6 Drive level charge density as a function of depletion width of two different types of a-Si solar cells (see text)
40
Figure 3.7 Illuminated J-V parameters of a-Si p-i-n solar cells by temperature measurement a-Si p-i-n solar cells for deposited p layers (a)μc-Si, (b) a-SiC, (c)a-SiO
41
Figure 3.8 The normalized initial open circuit voltage as a function of temperature of three different types of a-Si solar cells (see text)
Figure 3.9 The normalized initial short circuit current as a function of temperature of three different types of a-Si solar cells (see text)
Temperature (oC)
42
Figure 3.10 The normalized initial conversion efficiency as a function of temperature of three different types of a-Si solar cells (see text)
Figure 3.11 Forward bias J-V characteristics for a-Si solar cells with different temperature
43
Figure 4.1 Current-voltage (J-V) characteristics of μc-Si solar cells under standard illumination conditions
Figure 4.2 Quantum efficiency spectra for μc-Si solar cells prepared at different i-layer deposition pressures
44
Figure 4.3 Band diagram of p-i-n junction by oxygen diffuse grain boundary process
45
Figure 4.4 Dark and photo conductivity at room temperature for μc-Si solar cells prepared at different i-layer deposition pressures
Figure 4.5 Dark conductivity at room temperature and activation energy measured at 300K-370K for μc-Si solar cells prepared at different i-layer deposition pressures
3 4 5 6 7 8 9
46
Figure 4.6(a) Capacitance versus dc bias for μc-Si solar cells at i-layer deposition pressure: 4Torr. The measuring frequency is 100Hz and the temperature is 300K.The amplitude of the alternating voltage is 25mV、50 mV、75 mV、100 mV, respectively
Figure 4.6(b) Drive level charge density versus depletion width in the solar cell depicted in Figure 4.6(a)
Voltage (V)
47
Figure 4.7(a) Capacitance versus dc bias for μc-Si solar cells at i-layer deposition pressure : 6Torr. The measuring frequency is 100Hz and the temperature is 300K. The amplitude of the alternating voltage is 25mV、50 mV、75 mV、100 mV, respectively
Figure 4.7(b) Drive level charge density versus depletion width in the solar cell depicted in Figure 4.7(a)
Voltage (V)
48
Figure 4.8(a) Capacitance versus dc bias for μc-Si solar cells at i-layer deposition pressures : 8Torr. The measuring frequency is 100Hz and the temperature is 300K.
The amplitude of the alternating voltage is 25mV、50 mV、75 mV、100 mV, respectively
Figure 4.8(b) Drive level charge density versus depletion width in the solar cell depicted in Figure 4.8(a)
Voltage (V)
49
Figure 4.9 Drive level charge density as a function of depletion width of for μc-Si solar cells prepared at different i-layer deposition pressures (see text)
Volatage (V)
Figure 4.10(a) Forward bias J-V characteristics for μc-Si solar cells prepare at i layer deposition pressure (4Torr) with different temperature
Depletion width (um)
50
Figure 4.10(b) Forward bias J-V characteristics for μc-Si solar cells prepare at i layer deposition pressure (6Torr) with different temperature
Figure 4.10(c) Forward bias J-V characteristics for μc-Si solar cells prepare at i layer deposition pressure (8Torr) with different temperature
Volatage (V)
51
Figure 4.11 Illuminated J-V parameters of μc-Si p-i-n solar cells by temperature measurement for i layers deposited at deposition pressure (a) 4Torr, (b) 6Torr, (c) 8Torr
52
Figure 4.12 The normalized initial open circuit voltage as a function of temperature of μc-Si solar cells prepared at different i-layer deposition pressures(see text)
Figure 4.13 The normalized initial short circuit current as a function of temperature of μc-Si solar cells prepared at different i-layer deposition pressures (see text)
Temperature (oC)
53
Figure 4.14 The normalized initial conversion efficiency as a function of temperature of μc-Si solar cells prepared at different i-layer deposition pressures (see text)
Temperature (oC)
20 30 40 50 60 70 80 90
Normalized Efficiency (%)
0.86 0.88 0.90 0.92 0.94 0.96 0.98 1.00 1.02
4Torr 6Torr 8Torr
54
Table
Table 3.1 Illuminated J-V parameters of a-Si p-i-n solar cells for deposited different p layers
Table 3.2 Parameters of change of a-Si p-i-n solar cells for deposited different p layers by temperature effect
P-layer
∆Voc ∆Jsc ∆Efficiencyμc-Si
-4.63% 2.94% 1.13%a-SiC
-3.55% 1.17% 3.41%a-SiO
-1.96% 0.7% 14.8%Sample P-layer Voc (V)
Jsc (mA/cm2)
FF Efficiency (%)
A μc-Si 0.71 12.0 0.57 4.79
B a-SiC 0.78 11.3 0.63 5.43
C a-SiO 0.81 11.5 0.65 5.75
55
Table 3.3 Temperatures correspond to the value of n and J0 of a-Si p-i-n solar cells for deposited μc-Si p layers at V=0.1V~0.5V, V=0.7V~0.8V, V=1.2~1.3V, respectively
P layer : μc-Si P layer : μc-Si P layer : μc-Si
n J0 n J0 n J0
25℃ 8.1 2.1E-04 3.5 7.4E-06 18.2 2.1E-02
65℃ 8.4 6.2E-04 3.5 1.9E-05 1612 2.4E-02
85℃ 7.7 1.6E-03 3.6 1.2E-04 15.4 3.0E-02
Table 4-1 Illuminated J-V parameters of μc-Si p-i-n solar cells for i layers deposited at different deposition pressure
Sample Pressure (Torr)
Voc (V)
Jsc (mA/cm2)
FF Efficiency (%)
Rs (Ω)
Rsh (Ω)
A 4.0 0.48 9.71 0.51 2.34 7.45 223.78
B 6.0 0.42 14.6 0.61 3.73 3.88 549.04
C 8.0 0.45 17.9 0.62 5.05 3.46 1447.97
56
Table4-2 The parameters of μc-Si p-i-n solar cells for i layers deposited at different deposition pressure
Table4-3 Temperatures correspond to the value of n and J0 of μc-Si p-i-n solar cells for i layers deposited at different deposition pressure and (a) at V=0.2V~0.4V (b)at V=0.6V~1V
57
(b)
4Torr 6Torr 8Torr
n J0 n J0 n J0
25℃ 6.7 2.8E-04 7.4 5.7E-04 7.7 3.4E-04
45℃ 7.7 1.8E-04 7.1 6.2E-04 7.1 4.1E-04
65℃ 8.1 2.2E-04 7.1 6.4E-04 7.0 3.7E-04
85℃ 8.3 2.1E-04 6.8 8.5E-04 6.9 6.3E-04
Table4-4: Parameters of change of μc-Si p-i-n solar cells for i layers deposited at different deposition pressure by temperature effect