**3.6 Photoelectrical properties of a-Si:H:Cl and μc-Si:H:Cl films**

Fig. 25 shows the relation between the dark and photo conductivities for the μc-Si:H:Cl films fabricated by increasing the SiH2Cl2 flow rate at the substrate temperatures of 250°C and 400°C. The photosensitivity reached at 5-6 orders of magnitude at room temperature. The level of photoconductivity was 10-5 S/cm under 100 mW/cm2 white light exposure. The dark and photo-conductivities were the order of 10-12 and 10-5 S/cm, respectively, which shows highly photosensitive films. Fig.26 shows the activation energies for the μc-Si:H:Cl films fabricated by increasing the SiH2Cl2 flow rate at the substrate temperatures of 250°C and 400°C The activation energies of electrical conductivity were 0.40-0.80 eV, suggesting that both a-Si:H:Cl and µc-Si:H:Cl films were intrinsic semiconductor films.

Novel Deposition Technique for Fast Growth

the substrate temperatures of 250°C and 400°C.

Fig. 27. The structure of the p-i-n solar cell

p-type Si:H:Cl

n-type Si:H:Cl

glass

of Hydrogenated Microcrystalline Silicon Thin-Film for Thin-Film Silicon Solar Cells 377

Fig. 26. Activation Energies,⊿**E** for the μc-Si:H:Cl films as a function of SiH2Cl2 flow rate at

deposition of ZnO:Al and p-type Si layers on SnO2 coated glass, respectively by rf magnetron sputtering and plasma CVD methods, μc-Si:H:Cl film with a 2-µm-thickness is fabricated using a high-density microwave plasma as a photovoltaic layer and n-type Si layer was fabricated using conventional rf plasma CVD method. When the samples were being transported between the rf chamber and MWP chamber, they were exposed to air. Subsequently, ZnO:Al and Ag layers were deposited as a top electrode using a shadow mask with a 5×5 mm2 holes. Table 3 shows the typical deposition conditions for p, i and n layers, respectively. Table 4 shows the typical deposition conditions for ZnO:Al, Ag layers fabricated by rf magnetron sputtering. The photocurrent-voltage, I-V characteristics under AM 1.5, 100mW/cm2 exposure condition are measured and the performance of solar cell is characterized with open circuit voltage, Voc, short circuit current, Isc, fill factor, FF and conversion efficiency, η. The collection

efficiency was also measured from 300 to 1200 nm under bias light conditions.

Ag (25mm2

(25mm2)

ZnO:Al

ZnO:Al i-type Si:H:C

**Light** 

SnO2(

ZnO:Al

)

**Surface Texture**

Fig. 24. XRD and Raman spectra of the μc-Si:H:Cl films fabricated at different flow rate of SiH2Cl2 at Ts of 250 and 400C.

Fig. 25. Dark and photo conductivities for the μc-Si:H:Cl films as a function of SiH2Cl2 flow rate at the substrate temperatures of 250°Cand 400°C

#### **4. Preliminary results of p-i-n structure μc-Si:H:Cl thin-film solar cells**

The preliminary result of Si thin-film solar cells using μc-Si:H:Cl thin-film fabricated by the high-density microwave plasma (MWP) of a SiH2Cl2-H2 mixture are shown here. High-rate grown μc-Si:H:Cl thin-films were applied to p-i-n structure Si thin-film solar cells as intrinsic absorption layer. The solar cell was fabricated using a single chamber system. The structure of the solar cell TCO/ZnO:Al/p-i-n/ZnO:Al/Ag is as shown in Fig. 27. After the

Fig. 24. XRD and Raman spectra of the μc-Si:H:Cl films fabricated at different flow rate of

Fig. 25. Dark and photo conductivities for the μc-Si:H:Cl films as a function of SiH2Cl2

The preliminary result of Si thin-film solar cells using μc-Si:H:Cl thin-film fabricated by the high-density microwave plasma (MWP) of a SiH2Cl2-H2 mixture are shown here. High-rate grown μc-Si:H:Cl thin-films were applied to p-i-n structure Si thin-film solar cells as intrinsic absorption layer. The solar cell was fabricated using a single chamber system. The structure of the solar cell TCO/ZnO:Al/p-i-n/ZnO:Al/Ag is as shown in Fig. 27. After the

**4. Preliminary results of p-i-n structure μc-Si:H:Cl thin-film solar cells** 

flow rate at the substrate temperatures of 250°Cand 400°C

SiH2Cl2 at Ts of 250 and 400C.

Fig. 26. Activation Energies,⊿**E** for the μc-Si:H:Cl films as a function of SiH2Cl2 flow rate at the substrate temperatures of 250°C and 400°C.

deposition of ZnO:Al and p-type Si layers on SnO2 coated glass, respectively by rf magnetron sputtering and plasma CVD methods, μc-Si:H:Cl film with a 2-µm-thickness is fabricated using a high-density microwave plasma as a photovoltaic layer and n-type Si layer was fabricated using conventional rf plasma CVD method. When the samples were being transported between the rf chamber and MWP chamber, they were exposed to air. Subsequently, ZnO:Al and Ag layers were deposited as a top electrode using a shadow mask with a 5×5 mm2 holes. Table 3 shows the typical deposition conditions for p, i and n layers, respectively. Table 4 shows the typical deposition conditions for ZnO:Al, Ag layers fabricated by rf magnetron sputtering. The photocurrent-voltage, I-V characteristics under AM 1.5, 100mW/cm2 exposure condition are measured and the performance of solar cell is characterized with open circuit voltage, Voc, short circuit current, Isc, fill factor, FF and conversion efficiency, η. The collection efficiency was also measured from 300 to 1200 nm under bias light conditions.

Fig. 27. The structure of the p-i-n solar cell

Novel Deposition Technique for Fast Growth

B2H6 (sccm) 9

**5. Conclusion**

Table 3. Typical deposition conditions for p, i and n layers

Table 4. Typical deposition condition for ZnO:Al and Ag layers

of Hydrogenated Microcrystalline Silicon Thin-Film for Thin-Film Silicon Solar Cells 379

Substrate Distance (mm) 20 60 20 Substrate Temperature (◌ْ ◌ْ C) 250 250 250 Power (W) 5 700 5 Pressure (mTorr) 200 120 200 H2 (sccm) 61 15 55 SiH2Cl2 (sccm) 3 3 3 PH3 (sccm) 15

Substrate Position (cm) 6 6 6 Substrate Temperature (°C) 350 250 250 RF Power (W) 100 100 50 Pressure (Pa) 2.5 2.5 2.5 thickness (Å) 2500 2500 1500

Fig.28 illustrates photocurrent –voltage characteristics for Si:H:Cl thin-film solar cells under 100 mW/cm2 white light exposure. Fig. 28a shows the I-V characteristics for the cell using μc-Si:H:Cl films fabricated at 20 Å/s by the high-density microwave plasma CVD of SiH2Cl2. The 5-6% efficiencies have been achieved for the cells fabricated by the conventional rf plasma-CVD method. However, the performance is still poor and the open circuit voltage, (Voc):0.54 V, short circuit density, (Jsc):2.15 mA/cm2, Fill Factor, FF:0.5236 and the conversion efficiency was 0.5236% in the cell made by the high-density microwave plasma from SiH2Cl2 but solar cell performance is confirmed by the high-density microwave plasma from SiH2Cl2 for the first time. The diffusion of Boron and Chlorine happens easily in i-layer by the high-density microwave plasma. Moreover, the etching reaction of p layer has occurred because of the hydrogen plasma. It is required to evaluate not only a single film but it is also necessary to evaluate the each interface i.e. AZO/p, p/i and i/n in order to improve the solar cell performance. More over precise control of p/i, i/n, AZO/p interface formation is needed for obtaining the further high performance.

The highly photoconductive and crystallized μc-Si:H:Cl films with less volume fraction of void and defect density were synthesized using the high-density and low-temperature microwave plasma source of a SiH2Cl2-H2 mixture rather than those from SiH4 while maintaining a high deposition rate of 27 Å/s. The μc-Si:H:Cl film possesses a μc-Si and a-Si mixture structure with less volume fraction of voids. The role of chlorine in the growth of μc-Si:H:Cl films is the suppression of the excess film crystallization at the growing surface. H termination of growing surface is more effective to suppress the defect density rather than that of Cl termination. The fast deposition of the μc-Si:H:Cl film with low defect density of 3-4 ×1015 cm-3 is achieved with reducing Cl concentration during the film growth. Both a-Si:H:Cl and µc-Si:H:Cl films show

p(RF) i(MW) n(RF)

ZnO:Al(front side) ZnO:Al(back side) Ag

Fig. 28. (a) Photocurrent-voltage characteristics under AM 1.5 exposure condition and (b) QE spectra under -1V biased conditions of Si thin-film solar cells using a 1µm-thick μc-Si:H:Cl layer by high-density microwave plasma source.


Table 3. Typical deposition conditions for p, i and n layers


Table 4. Typical deposition condition for ZnO:Al and Ag layers

Fig.28 illustrates photocurrent –voltage characteristics for Si:H:Cl thin-film solar cells under 100 mW/cm2 white light exposure. Fig. 28a shows the I-V characteristics for the cell using μc-Si:H:Cl films fabricated at 20 Å/s by the high-density microwave plasma CVD of SiH2Cl2. The 5-6% efficiencies have been achieved for the cells fabricated by the conventional rf plasma-CVD method. However, the performance is still poor and the open circuit voltage, (Voc):0.54 V, short circuit density, (Jsc):2.15 mA/cm2, Fill Factor, FF:0.5236 and the conversion efficiency was 0.5236% in the cell made by the high-density microwave plasma from SiH2Cl2 but solar cell performance is confirmed by the high-density microwave plasma from SiH2Cl2 for the first time. The diffusion of Boron and Chlorine happens easily in i-layer by the high-density microwave plasma. Moreover, the etching reaction of p layer has occurred because of the hydrogen plasma. It is required to evaluate not only a single film but it is also necessary to evaluate the each interface i.e. AZO/p, p/i and i/n in order to improve the solar cell performance. More over precise control of p/i, i/n, AZO/p interface formation is needed for obtaining the further high performance.
