**2. Experimental**

the e-h pairs can also depend upon built-in electric field created by doped p-type and n-type layers [5], and thus degree and efficiency of doping of these layers are also important.

Along with its wider optical gap, the doped window layer or the top p-layer is generally made thinner as well [6], so that more light can enter into the active region of the device. However, with a thinner p-type layer the output voltage also get reduced [7,8], leading to more recombination loss of the photo generated charge carriers. Similarly, if optical gap of the window layer is high, then also the absorption loss at the p-type layer reduces. So, a wider optical gap thicker p-type layer appears to be a good option for a solar cell window layer. However, it is known that with increased carbon content within the material, optical gap increases [9,10] and the wider optical gap is usually associated to lower dark conductiv‐ ity [11], and higher activation energy (Ea). As a result the higher optical gap of the p-type

There are several different types of window layer one can use, like hydrogenated amor‐ phous silicon oxide (a-SiO:H) [12], hydrogenated amorphous silicon carbide (a-Si1-xCx:H) [1,13], hydrogenated amorphous silicon (a-Si:H) [14] etc and micro-crystalline or nano-crys‐ talline version of these materials. Out of these, wide band gap a-Si1-xCx:H and nc-Si:H mate‐

Being amorphous in nature and containing hydrogen (H) and carbon (C) atoms in the mate‐ rial the composition and local bonding structure of the characteristic property of the materi‐ al is thus partly determined by microstructure within the material. A microstructure is a local non-uniformity of the material, and is generally used to indicate the density of SiHn or CHn type poly-hydrides in the material, where 1 ≤ n ≤ 3. Such a microstructure can also be

The carbon-silicon bonds lead to higher optical gap of the material and thus the increased carbon fraction x in a-Si1-xCx:H leads to higher optical gap of the material [1,9,17,18]. This higher optical gap results in higher optical transparency of the material, making it more suitable for a transparent window layer of a p-i-n type solar cell. It is also known that boron doping of amorphous silicon alloy material leads to reduction in optical gap [19]. Thus, a

In a multiple- junction amorphous silicon solar cell, multiple p-i-n type structures are joined in tandem [20]. The multiple junction solar cells are also known as multi-junction solar cell. The advantage of such a solar cell is that the open circuit voltage (Voc) becomes higher, and a wider spectral range of solar radiation can be absorbed in aggregate to the component cells. In this re‐ spect double (DJ) and triple junction (TJ) cells have been extensively studied in recent past [21-24]. As purpose of the DJ or TJ cell is the PV energy conversion by utilizing a wider spectral range, so tailoring of the band gap of the component cells become very important part of the design. In a suitable design, the top cell should have wider optical gap so that shorter wave‐ length light can be absorbed but the longer wavelength light will remain unabsorbed, while the middle cell should absorb the middle part and the bottom cell should absorb the longer wavelength part of the solar spectra. Thus, for the single p-i-n type cell or multiple-junction cell, a wide band gap window layer becomes a very significant component of the device.

called a void structure as well, that may be deteriorative for the material [15,16].

suitable boron doped p-a-Si1-xCx:H can become one of the best suited window layers.

layer may lead to lower output voltage from the device.

rials are two of the most promising materials.

290 Photodiodes - From Fundamentals to Applications

#### **2.1. Deposition of Silicon Alloy Films**

We prepared amorphous type p-a-Si1-xCx:H, a-Si:H, n-a-Si:H and nano-crystalline p-nc-Si:H, i-nc-Si:H, n-ncSi:H films, characterized them and applied in single junction, double junction and triple junction solar cells. We used RF PECVD, VHF PECVD, HW-CVD, for depositing silicon alloy materials, sputtering for AZO film deposition and thermal evaporation for met‐ al electrode deposition. The silane (SiH4), methane (CH4), hydrogen (H2), diborane (B2H6) (1% in H2), phosphine (PH3)(1% in H2) were the source gases for various films, where the SiH4, CH4, H2 were used for a-Si1-xCx:H alloy materials, SiH4, H2 for a-Si:H and nc-Si:H films, B2H6 was used as a p-type dopant gas and PH3 as the n-type dopant one.

The p-a-Si1-xCx:H films were deposited by 13.56 MHz RF PECVD with CH4, SiH4, H2, B2H6 source gases, at substrate temperature (Ts) of 200o C. For optoelectronic characterization, the films were deposited on 25mm×25mm sized Corning 1737 glass substrates and for Fourier transform infra red (FTIR) spectroscopic study we used (100) oriented p-type c-Si wafers. Later, selective samples are used for the p-type layer of the p-i-n type solar cells. Prior to film deposition the substrates were cleaned in acetone, methanol and de-ionized water. A 10-8 Torr base pressure of the reaction chamber was maintained prior to the film depositions.

The intrinsic a-Si:H and nc-Si:H absorption layers were deposited by 60MHz VHF PECVD and Hot Wire CVD methods. Deposition condition for one of the i-type layers is, H2 flow rate 60 sccm, SiH4 flow rate 7 sccm, RF power 8 Watt, pressure 300 mTorr. Deposition condition for ntype layer is, H2 flow rate 10 sccm, SiH4 flow rate 5 sccm, PH3 flow rate 1% to that of silane, RF power 6 Watt, pressure 300 mTorr. Thickness and optical gap of i-type layer is maintained at ~200 nm and 1.75 eV, and that of n-type layer at ~30 nm and 1.7 eV respectively.

posited on the glass substrates, with planar electrode configuration. The photoconductivity

Single- and Multiple-Junction p-i-n Type Amorphous Silicon Solar Cells with p-a-Si1-xCx:H and nc-Si:H Films

gen content C(H) as well as hydrogen bonding configurations of the films were estimated by FTIR spectroscopy [37]. The hydrogen content can be obtained from the absorption peak at 640 cm-1 that includes the rocking mode of bonded hydrogen. To get absorption strength α640(ω) of rocking mode, absorption peak at 640 cm-1 is fitted to a Gaussian function. From the fitted function, the hydrogen content was calculated, using the following equation.

640

w

Where A640 is a constant needed to calculate hydrogen content from rocking mode, and I640 is

Textured TCO coated glasses were used for fabrication of p-i-n type solar cells. After the deposition of the p-, i-, n-type layers, either the solar cell was completed by depositing Ag electrodes or aluminum doped zinc oxide (AZO) layer was deposited by RF magnetron sputtering and then Ag layer was deposited. This AZO/Ag layer combination works as a good back reflector (BR). In order to achieve clear electrical connection the cell was wet etch‐ ed using HCl (for removal of AZO in the BR) and by reactive ion etching in CF4 plasma.

The p-type window layer of the cell was tested with various p-a-Si1-xCx:H materials and pnc-Si:H. In multiple- junction cell we used intrinsic a-Si:H as well as nc-Si:H materials.

For the single p-i-n type a-Si:H solar cell, 8 ~ 20nm thick p-a-Si1-xCx:H was used as p-type layer and to anyalize the interface characteristics with front TCO, p-type nc-Si:H thin film was also inserted between TCO and p-a-Si1-xCx:H layer [38] and improved performance of the solar cell was observed. For the p-i-n nc-Si:H solar cell, about 15nm thick nc-Si:H was used as p type win‐ dow layer to minimize the band mismatching with i-type nc-Si:H layer. The a-Si:H/nc-Si:H double junction (DJ) cell and a-Si:H/nc-Si:H/nc-Si:H triple junction (TJ) solar cells were also fabricated. To improve performance of the multiple-junction solar cells the tunnel junction in

The nc-Si:H bottom cells were separately fabricated in the form of a single p-i-n type cell struc‐ ture, measured its characteristic properties and then a few of the selected cells were used in multiple-junction solar cells. Fig. 1 shows the schematic diagram of a nc-Si:H thin film solar cells. Unlike the a-Si:H solar cells, p-type nc-Si:H thin film was used as a window layer to mini‐

the form of n-nc-Si:H/p-nc-Si:H or n-a(nc)-Si:H/AZO/p-nc-Si:H structures were used.

**2.5. nc-Si:H bottom cell using 60MHZ VHF CVD**

w

( ) *I d* a w

640

) light generated by solar simulator. The hydro‐

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293

640 640 *CH A I* ( ) = (3)

<sup>=</sup> ò (4)

was measured under AM1.5 (100mW/cm2

the integrated absorption coefficient.

**2.4. Fabrication of solar cells**

Electrical characteristics of the thin films were measured in a planar electrode configura‐ tion. Auger analysis was performed in order to estimate fractional carbon content (x) of the material.

#### **2.2. Deposition of intrinsic nc-Si:H thin film by 60MHZ VHF CVD**

Table 1 shows the deposition conditions of nc-Si:H thin film. The nc-Si:H films were pre‐ pared at higher hydrogen dilution.


**Table 1.** Deposition condition of nc-Si:H films at various hydrigen dilution, RSi = SiH4/(SiH4+H2), with SiH4 flow rate as 7 sccm, RF power 8Watt, deposition time 60 min, dsh =2cm that is the electrode seperation of the PECVD system.

#### **2.3. Characterization of Si alloy films**

Raman and spectroscopy and X-ray diffraction (XRD) spectroscopy were used to character‐ ize crystallinity of the films. Usually the nanocrystals were embedded in amorphous silicon phase and thus the characteristic spectra of both the crystalline and amorphous phase is visi‐ ble in the spectroscopic analysis. The Raman spectra of nc-Si:H silicon thin film is composed of 520cm-1 peak (of intensity Ic) of crystalline phase and 480cm-1 peak (of intensity Ia) of amorphous phase [27]. In polycrystalline silicon thin film, the peak is shifted to lower wave‐ number because of the amorphous phase and occurs at 517-518cm-1. The crystalline volume fraction (Xc) was calculated using relation [28, 34, 35]

$$X\_c = (I\_c) / (I\_c + I\_a) \tag{1}$$

The average crystal size was obtained from

$$d\_{\mathcal{A}\_{\text{Raman}}} = 2\pi \sqrt{B / \Delta o} \tag{2}$$

where Δω is the shift of Raman peak for μc-Si:H with respect to that of c-Si, B=2.0cm-1.nm2 [36]. The dark conductivity (σd) and photoconductivity (σph) were measured for the films de‐ posited on the glass substrates, with planar electrode configuration. The photoconductivity was measured under AM1.5 (100mW/cm2 ) light generated by solar simulator. The hydro‐ gen content C(H) as well as hydrogen bonding configurations of the films were estimated by FTIR spectroscopy [37]. The hydrogen content can be obtained from the absorption peak at 640 cm-1 that includes the rocking mode of bonded hydrogen. To get absorption strength α640(ω) of rocking mode, absorption peak at 640 cm-1 is fitted to a Gaussian function. From the fitted function, the hydrogen content was calculated, using the following equation.

$$C(H) = A\_{640} I\_{640} \tag{3}$$

$$I\_{640} = \int \frac{\alpha\_{640}(\alpha)}{\alpha} d\alpha \tag{4}$$

Where A640 is a constant needed to calculate hydrogen content from rocking mode, and I640 is the integrated absorption coefficient.

#### **2.4. Fabrication of solar cells**

The intrinsic a-Si:H and nc-Si:H absorption layers were deposited by 60MHz VHF PECVD and Hot Wire CVD methods. Deposition condition for one of the i-type layers is, H2 flow rate 60 sccm, SiH4 flow rate 7 sccm, RF power 8 Watt, pressure 300 mTorr. Deposition condition for ntype layer is, H2 flow rate 10 sccm, SiH4 flow rate 5 sccm, PH3 flow rate 1% to that of silane, RF power 6 Watt, pressure 300 mTorr. Thickness and optical gap of i-type layer is maintained at

Electrical characteristics of the thin films were measured in a planar electrode configura‐ tion. Auger analysis was performed in order to estimate fractional carbon content (x) of

Table 1 shows the deposition conditions of nc-Si:H thin film. The nc-Si:H films were pre‐

**Table 1.** Deposition condition of nc-Si:H films at various hydrigen dilution, RSi = SiH4/(SiH4+H2), with SiH4 flow rate as 7 sccm, RF power 8Watt, deposition time 60 min, dsh =2cm that is the electrode seperation of the PECVD system.

Raman and spectroscopy and X-ray diffraction (XRD) spectroscopy were used to character‐ ize crystallinity of the films. Usually the nanocrystals were embedded in amorphous silicon phase and thus the characteristic spectra of both the crystalline and amorphous phase is visi‐ ble in the spectroscopic analysis. The Raman spectra of nc-Si:H silicon thin film is composed of 520cm-1 peak (of intensity Ic) of crystalline phase and 480cm-1 peak (of intensity Ia) of amorphous phase [27]. In polycrystalline silicon thin film, the peak is shifted to lower wave‐ number because of the amorphous phase and occurs at 517-518cm-1. The crystalline volume

> 2 / *Raman d B* = D p

 w

where Δω is the shift of Raman peak for μc-Si:H with respect to that of c-Si, B=2.0cm-1.nm2 [36]. The dark conductivity (σd) and photoconductivity (σph) were measured for the films de‐

( )/( ) *X I II c c ca* = + (1)

(2)

H2(sccm) 60 ~ 185 RSi 10.4% ~ 3.6% Ts.(°C) 140°C & 200

~200 nm and 1.75 eV, and that of n-type layer at ~30 nm and 1.7 eV respectively.

**2.2. Deposition of intrinsic nc-Si:H thin film by 60MHZ VHF CVD**

the material.

pared at higher hydrogen dilution.

292 Photodiodes - From Fundamentals to Applications

**2.3. Characterization of Si alloy films**

fraction (Xc) was calculated using relation [28, 34, 35]

The average crystal size was obtained from

Textured TCO coated glasses were used for fabrication of p-i-n type solar cells. After the deposition of the p-, i-, n-type layers, either the solar cell was completed by depositing Ag electrodes or aluminum doped zinc oxide (AZO) layer was deposited by RF magnetron sputtering and then Ag layer was deposited. This AZO/Ag layer combination works as a good back reflector (BR). In order to achieve clear electrical connection the cell was wet etch‐ ed using HCl (for removal of AZO in the BR) and by reactive ion etching in CF4 plasma.

The p-type window layer of the cell was tested with various p-a-Si1-xCx:H materials and pnc-Si:H. In multiple- junction cell we used intrinsic a-Si:H as well as nc-Si:H materials.

For the single p-i-n type a-Si:H solar cell, 8 ~ 20nm thick p-a-Si1-xCx:H was used as p-type layer and to anyalize the interface characteristics with front TCO, p-type nc-Si:H thin film was also inserted between TCO and p-a-Si1-xCx:H layer [38] and improved performance of the solar cell was observed. For the p-i-n nc-Si:H solar cell, about 15nm thick nc-Si:H was used as p type win‐ dow layer to minimize the band mismatching with i-type nc-Si:H layer. The a-Si:H/nc-Si:H double junction (DJ) cell and a-Si:H/nc-Si:H/nc-Si:H triple junction (TJ) solar cells were also fabricated. To improve performance of the multiple-junction solar cells the tunnel junction in the form of n-nc-Si:H/p-nc-Si:H or n-a(nc)-Si:H/AZO/p-nc-Si:H structures were used.

#### **2.5. nc-Si:H bottom cell using 60MHZ VHF CVD**

The nc-Si:H bottom cells were separately fabricated in the form of a single p-i-n type cell struc‐ ture, measured its characteristic properties and then a few of the selected cells were used in multiple-junction solar cells. Fig. 1 shows the schematic diagram of a nc-Si:H thin film solar cells. Unlike the a-Si:H solar cells, p-type nc-Si:H thin film was used as a window layer to mini‐ mize the interface defects arising from the band mismatch with i-nc-Si:H. To form p type nc-Si:H thin film by 13.56 MHz PECVD, higher H2 gas flow rates were used (see Table 2).

**2.6. Structure and fabrication of multiple- junction solar cell**

cells were kept as 2.0 μm and 3.2 μm respectively.

**a-Si:H top-cell**

**nc-Si:H bottom-cell**

Fig. 1(b) shows the schematic diagram of a double junction and Fig. 1(c) shows that of a triple junction solar cell. Fluorine doped tin oxide (FTO) coated glass (Asahi-U type glass) or tex‐ tured AZO was used for solar cell front electrode and over which the cells were deposited. P-I-N a-Si:H top and nc-Si:H bottom cells were deposited in turn in multi-chamber system. For the tunnel junctions at the n-p interface, it was made either nano crystalline or AZO layer was de‐

Single- and Multiple-Junction p-i-n Type Amorphous Silicon Solar Cells with p-a-Si1-xCx:H and nc-Si:H Films

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295

Fig. 1(c) shows the structure of a-Si:H/nc-Si:H/nc-Si:H triple junction thin solar cell. The dep‐ osition conditions are given in Table 3 for double junction cell and Table 4 for a triple junc‐ tion cell. The thickness of a-Si:H top intrinsic layer was 150nm, the thickness of nc-Si:H middle absorption layer was 2.0μm and thickness of bottom absorption layer was 3.2μm. No inter-layer for TRJ was used between the cells and to improve the tunnel junction, the nanocrystalline (n-nc-Si:H)-(p nc-Si:H) layers were used. For back electrode, AZO/Ag BR was used. For a MJ solar cell, current matching is an important step for optimization of de‐ vice performance. We optimized the component cell structures with the help of QE spectra, after which the i-layer thickness of the middle and bottom cells of a triple junction (TJ) solar

**p nc-Si:H p-a-Si1-xCx:H i a-Si:H n a-Si:H**

**p nc-Si:h i nc-Si:H n a-Si:H**

posited in between the n-type and p-type layers of the successive cells as n/AZO/p.

SiH4(sccm) 1 6 7 5 H2(sccm) 180 5 60 5 B2H6(sccm)×100 0.4 1-4 - - RF power (W) 16 6 8 6 Pressure (mTorr) 500 300 300 300 Thickness <5nm 20nm 100-300nm 20-30nm

SiH4(sccm) 1 5 5 H2(sccm) 180 95 5 RF power (W) 16 16 6 Pressure (mTorr) 500 300 300 Thickness 20nm 1.7 μm 20-30nm

**Table 3.** Deposition condition for a double junction solar cell. The top cell was deposited with textured front TCO, CH4 flow rate for p-a-Si1-xCx:H as 16 sccm, 1% gas phase doping of n-type layer with PH3. The bottom cell's p-type layer was 0.4% doped with B2H6, with no CH4 flow and the n-layer as 1% doped. With AZO/Ag as BR, and less than 10nm thick

AZO interlayer as a tunnel junction in between n-type and p-type layers of the cells.


**Table 2.** Deposition condition for a nanocrystalline single p-i-n type solar cell in a RF PECVD system, with 0.36cm2 cell area. For BR and back electrode, a 100nm AZO and 500 nm Ag/Al metal layers were deposited at the back of the cell. The n-layer was doped by 1% with phosphine.

**Figure 1.** Schematic diagram of (a) single p-i-n type (b) double junction, (c) triple junction solar cell, where M stands for metal electrode.

For n-type layer of the cell, a-Si:H or nc-Si:H thin film was used. The AZO(~100nm) was depos‐ ited by RF magnetron sputtering and Ag/Al metal layers were deposited by thermal evapora‐ tion. The Al in back reflector (BR) electrode also acts as a protection layer to minimize the damage on Ag during electrode isolation dry etching. The fabricated solar cell areas were 0.36cm2 . The area is controlled by using shadow mask during electrode deposition.

#### **2.6. Structure and fabrication of multiple- junction solar cell**

mize the interface defects arising from the band mismatch with i-nc-Si:H. To form p type nc-

SiH4(sccm) 0.2 ~ 1 ~ 7 5 H2(sccm) ~ 180 ~ 95 5 B2H6(sccm) ~ 1 - - RF power (W) 16 16 6 Pressure (mTorr) 500 300 300 Thickness 30nm 2μm 30nm

**Table 2.** Deposition condition for a nanocrystalline single p-i-n type solar cell in a RF PECVD system, with 0.36cm2 cell area. For BR and back electrode, a 100nm AZO and 500 nm Ag/Al metal layers were deposited at the back of the cell.

**Figure 1.** Schematic diagram of (a) single p-i-n type (b) double junction, (c) triple junction solar cell, where M stands

For n-type layer of the cell, a-Si:H or nc-Si:H thin film was used. The AZO(~100nm) was depos‐ ited by RF magnetron sputtering and Ag/Al metal layers were deposited by thermal evapora‐ tion. The Al in back reflector (BR) electrode also acts as a protection layer to minimize the damage on Ag during electrode isolation dry etching. The fabricated solar cell areas were

. The area is controlled by using shadow mask during electrode deposition.

The n-layer was doped by 1% with phosphine.

294 Photodiodes - From Fundamentals to Applications

for metal electrode.

0.36cm2

**p nc-Si:H i nc-Si:H n a(nc-Si):H**

Si:H thin film by 13.56 MHz PECVD, higher H2 gas flow rates were used (see Table 2).

Fig. 1(b) shows the schematic diagram of a double junction and Fig. 1(c) shows that of a triple junction solar cell. Fluorine doped tin oxide (FTO) coated glass (Asahi-U type glass) or tex‐ tured AZO was used for solar cell front electrode and over which the cells were deposited. P-I-N a-Si:H top and nc-Si:H bottom cells were deposited in turn in multi-chamber system. For the tunnel junctions at the n-p interface, it was made either nano crystalline or AZO layer was de‐ posited in between the n-type and p-type layers of the successive cells as n/AZO/p.

Fig. 1(c) shows the structure of a-Si:H/nc-Si:H/nc-Si:H triple junction thin solar cell. The dep‐ osition conditions are given in Table 3 for double junction cell and Table 4 for a triple junc‐ tion cell. The thickness of a-Si:H top intrinsic layer was 150nm, the thickness of nc-Si:H middle absorption layer was 2.0μm and thickness of bottom absorption layer was 3.2μm. No inter-layer for TRJ was used between the cells and to improve the tunnel junction, the nanocrystalline (n-nc-Si:H)-(p nc-Si:H) layers were used. For back electrode, AZO/Ag BR was used. For a MJ solar cell, current matching is an important step for optimization of de‐ vice performance. We optimized the component cell structures with the help of QE spectra, after which the i-layer thickness of the middle and bottom cells of a triple junction (TJ) solar cells were kept as 2.0 μm and 3.2 μm respectively.


**Table 3.** Deposition condition for a double junction solar cell. The top cell was deposited with textured front TCO, CH4 flow rate for p-a-Si1-xCx:H as 16 sccm, 1% gas phase doping of n-type layer with PH3. The bottom cell's p-type layer was 0.4% doped with B2H6, with no CH4 flow and the n-layer as 1% doped. With AZO/Ag as BR, and less than 10nm thick AZO interlayer as a tunnel junction in between n-type and p-type layers of the cells.


x 0.59y 0.23 = - (5)

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297

E 1.40 2.99x <sup>g</sup> = + (6)

*d a* = - <sup>0</sup> exp / [ ] *E kT* (7)

C temperature range. We observed that

for this range of y. The expression for x comes from the linear fit to the data points of Fig. 2(a). It may appear that while methane flow rate is zero the fractional carbon content will become negative. This conclusion is not realistic. The negative intercept of the linear equa‐ tion (or -0.23) may indicate the change in chemical kinetics, that comes into play in the chemical vapor of the RF PECVD system in presence of methane, in comparison to when

Optical gap (Eg) of the films were measured as the photon energy at which absorption coeffi‐

tent. The band gap of p-a-Si1-x Cx deposited ranges within 1.7 ~ 2.3 eV. It can be seen that Eg

The expression for Eg comes from the linear fit to the data points of Fig. 2(b). It may appear that for a-Si:H samples, where carbon content x=0 the optical gap of the sample will be 1.40 eV. However this not the case, as it is known that Eg of a-Si:H is ~1.7 eV and depends on hydrogen content. The reason may be the role played by carbon in amorphous network. At low carbon content of p-a-Si1-xCx:H samples, the number density of Si-H bonds decrease. In a-Si:H sample it's the Si-H bonds that helps enhancing optical gap. In p-a-Si1-xCx:H samples it has been found that Si-H bond density decreases and C-H bond density increases. Thus while carbon content of the p-a-Si1-xCx:H films were increased role of the Si-Si bonds on optical gap that remain un‐ changed, while number density of Si-H and C-H changes. Thus the role of bonded Si-H, C-H bonds on optical gap may be reflected in the factor 2.99x while the contribution of Si-Si bonds

Fig. 2(c) shows effect of C content on the dark conductivity and the related activation ener‐

where σ0 is a constant, k-Boltzmann constant, T temperature. Ea is estimated experimentally

as x increases, the dark conductivity decreases from 10-5 to 10-10 Scm-1 and the activation energy increases from 0.35 to over 0.8 eV. For p-type material the activation energy is the energy differ‐ ence between Fermi level and valence band mobility edge. Furthermore, the relatively higher value of activation energy of the samples may be because of lower doping, which is 0.17%, whereas normal doping used in solar cell is usually 1%. However, the trend in variation of Ea and σd becomes qualitatively obvious as the trend of the traces were nearly complementary to

C to 125o

on the optical gap may be contributing to the 1.40 constant of the equation for Eg.

gy. The σd and activation energy (Ea) were related by Arrhenius relation

s s

through slope of a plot of log(σd) vs 1/T in 25o

cm-1. Fig. 2(b) shows the change in the Eg of p-a-Si1-x Cx depending on the C con‐

Single- and Multiple-Junction p-i-n Type Amorphous Silicon Solar Cells with p-a-Si1-xCx:H and nc-Si:H Films

methane was absent.

increases almost linearly with x, where

cient is 104

**Table 4.** Deposition condition for a triple junction solar cell. All the n-layers of the cells were 1% doped with PH3, players of the bottom and middle cells were 0.4% doped, The top cell was deposited with textured front TCO, CH4 flow rate for p-a-Si1-xCx:H as 16 sccm. The p-type layer of the middle and the bottom cells were deposited with 0.4% B2H6 doping, no CH4 flow and the n-layer as 1% doped. With AZO/Ag BR, and less than 10nm thick AZO interlayer as a tunnel junction in between n-type and p-type layers of the cells. For the middle and the bottom cells the RF power was 16W for the p-, i-, n- layers. The cell area was 0.36cm2.
