- Email: [email protected]
Role of hydrazine monohydrate during texturization of large-area crystalline silicon solar cell fabrication
ARTICLE IN PRESS
Solar Energy Materials & Solar Cells 90 (2006) 3094–3101 www.elsevier.com/locate/solmat
Role of hydrazine monohydrate during texturization of large-area crystalline silicon solar cell fabrication U. Gangopadhyaya,b, Kyunghae Kimb, Ajoy Kandolb, Junsin Yib,, H. Sahaa a
IC Design and Fabrication Centre, Electronics and Tele-communication, Engineering Department, Jadavpur University, Kolkata 700032, India b School of Electrical and Computer Engineering, Sungkyunkwan University, 300 Chunchun-dong, Jangan-gu, Suwon 440-746, Republic of Korea Available online 24 July 2006
Abstract Reduction of optical losses in monocrystalline silicon solar cells by surface texturing is one of the important issues of modern silicon photovoltaic. For texturization during commercial monocrystalline silicon solar cell fabrication, a mixture of NaOH or KOH and isopropyl alcohol (IPA) is generally used in order to achieve good uniformity of pyramidal structure on the silicon surface. The interfacial energy between silicon and electrolyte should be reduced in order to achieve sufficient wettability for the silicon surface which in turn will enhance the pyramid nucleation. In this work, we have investigated the role of hydrazine monohydrate as a surface-active additive, which supplies OH ions after dissociation. This cuts down the IPA consumption during texturing without any loss of uniformity of textured pyramid. We are probably the first group to report such a novel idea of using hydrazine monohydrate addition in NaOH solution for texturization of solar cell. We were able to fabricate monocrystalline silicon solar cells with more than 85% yield in the range of 14–15% efficiency. r 2006 Elsevier B.V. All rights reserved. Keywords: Texturization; Hydrazine; IPA; Low cost; Silicon; Solar cell
Corresponding author. Tel.: +82 31 290 7139; fax: +82 31 290 7179.
E-mail address: [email protected] (J. Yi). 0927-0248/$ - see front matter r 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.solmat.2006.06.014
ARTICLE IN PRESS U. Gangopadhyay et al. / Solar Energy Materials & Solar Cells 90 (2006) 3094–3101
3095
1. Introduction Texturing of /1 0 0S oriented single crystal silicon substrates with appropriate antireflection coating (ARC) has become a well-established method in solar photovoltaic industry for minimizing the reflection loses. Many researchers [1,2] have shown the selective etching of /1 0 0S silicon by using sodium or potassium hydroxide solution. For monocrystalline silicon solar cells, anisotropic etch is used to form pyramidal structure that can collect the reflected light and trap the light inside the cells by internal reflection [3,4]. The most common etchant is the mixture of sodium hydroxide (NaOH) or potassium hydroxide (KOH) with water and isopropyl alcohol (IPA) [5,6]. In those etch solution, IPA can help not only to remove hydrogen bubbles but also to promote the formation of big pyramids. However, IPA easily pollutes the workshop and is expensive. Without IPA, NaOH solution does not always result in complete coverage of the surface with pyramids. One possible reason for this phenomenon is assumed to be an insufficient pyramid nucleation because of the poor wettability of silicon surface. The interfacial energy of silicon/electrolyte should be reduced in order to achieve sufficient wettability for the silicon surface which in turn can enhance the pyramidal nucleation. Mixing surface-active additives into the solution can reduce the interfacial energy [7,8]. IPA increases the wettability of the silicon surface but the rate of the silicon removal decreases strongly with increasing IPA concentration [9]. Hydrazine monohydrate was applied initially as the selective etchant for texturization. Normally higher temperature (490 1C) is selected during hydrazine selective texturization, because at that temperature hydrazine hydrate (N2H4, H2O) breaks in to ionized state and supply OH for texturization. In this paper, we report our investigation on the role of OH after ionization of hydrazine monohydrate in sodium hydroxide texturization solution. We have also reported the fabrication of high yield (485%) and high-efficiency (14–15%) monocrystalline silicon solar cells with this texturization approach. 2. Experimental 2.1. Texturization p-type /1 0 0S oriented monocrystalline silicon wafers with resistivity of about 1–5 O cm were used for the texturization. The etchant solution was heated using a heating plate and a flat polypropylene squire’s tub was used to cover the etchant vessel during etching to prevent the loss of chemical during texturization. The wafers were first dipped in a 8% NaOH solution at 75 1C for 2–3 min for damage etching followed by a dipping in the texturing bath. The concentrations of NaOH and hydrazine hydrate (1.8% and 4.3%, respectively) solutions were kept constant throughout the texturization process at a fixed bath temperature of 82 1C. The duration of the texturization was varied at four different values (Table 1). The etchant was not agitated during etching, because of the possibility of a detrimental effect on the characteristic reflectance of the textured samples. It was noticed that, after texturization using NaOH–N2H4, H2O texturization baths, all the wafers were equally textured without any spot on the surface. After texturing, the hemispherical surface reflectance was evaluated and compared with conventional NaOH texturized silicon surface, The surface morphology of the texturized
ARTICLE IN PRESS U. Gangopadhyay et al. / Solar Energy Materials & Solar Cells 90 (2006) 3094–3101
3096
Table 1 Experimental conditions adopted in the present study Batch Quantity NaOH no. of wafers conc. (%)
N2H4, H2O Time measured conc. (%) from the initial start of experiment (min)
Initial IPA conc. (%)
Additional IPA during each run (%)
Remarks
1
25
1.8
4.3
30
5
Nil
2
25
1.8
4.3
60
Nil
3.9
3
25
1.8
4.3
90
Nil
2.85
4
25
1.8
4.3
120
Nil
2.28
Uniform Texturization Uniform Texturization Uniform Texturization Uniform Texturization
silicon surface with two different methods (NaOH–N2H4, H2O and conventional NaOH) were also studied by scanning electron microscope (SEM). 2.2. Solar cell fabrication Monocrystalline silicon solar cells were fabricated using the conventional POCl3 diffusion, PECVD silicon nitride ARC and screen-printed metallization. All textured silicon wafers were diffused by n-type impurity in an open-tube furnace using conventional POCl3 diffusion source at 900 1C, with a 10 min pre-deposition followed by a 30 min drivein. After performing edge isolation, about 80 nm SiNx was deposited as an antireflection coating (ARC) at the front side of the wafer by means of PECVD at a temperature of 300 1C. The front and back metallization of the diffused texturized silicon wafers were carried out by screen printing technique using standard Al-paste (product no. FX 53-038, Ferro Electronic Materials) and Ag/Al paste (product no. 3398, Ferro Electronic Materials). This was followed by baking and co-firing at a temperature of 752 1C in a conveyer belt furnace. Back mesh structure has been used for the fabrication of the solar cells. Illuminated current–voltage (LIV) characteristic and spectral response (SR) studies of the fabricated monocrystalline solar cells were carried out and the results are presented. 3. Results and discussion From the different experimental conditions depicted in Table 1, it is observed that the amount of IPA added during each successive batch of texturization process has been reduced from 5% (first batch run) to 2.23% (fourth batch run) without any bubble spot on the texturized silicon wafers. The good surface finish of the texturized silicon even with low amount of IPA may be due to the dissociation of hydrazine hydrate leading to the supply OH ions to the NaOH bath. Actually, during the initial stages of experiment carried out with the first lot of wafers, the hydrazine monohydrate in the NaOH solution did not dissociate at the temperature of 82 1C, because it took longer time to dissociate at that temperature. With the increase of time, more hydrazine is dissociated and hence more
U. Gangopadhyay et al. / Solar Energy Materials & Solar Cells 90 (2006) 3094–3101
3097
Fig. 1. SEM picture of a typical texturized silicon surface using NaOH–N2H4, H2O texturization bath.
Fig. 2. SEM picture of a typical texturized silicon surface using conventional NaOH texturization bath.
ARTICLE IN PRESS 3098
U. Gangopadhyay et al. / Solar Energy Materials & Solar Cells 90 (2006) 3094–3101
14
Total Reflectance
12 10 8 6 4 2 0 NaOH-N2H4,H2O
NaOH
Texturized Bath Fig. 3. Total reflectance of texturized silicon surface using NaOH–N2H4, H2O and conventional NaOH texturization baths, respectively.
Table 2 Electrical parameters of NaOH–N2H4, H2O texturized monocrystalline silicon solar cells Description of texturization bath
Voc (V)
Isc (A)
Pm (W)
FF
Efficiency (%)
Rs (m O)
Rsh (O)
I01 (A)
New NaOH– N2H4, H2O bath
0.595
3.399
1.47
0.73
14.18
21
125.40
4.13 10
I02 (A) 8
1.23 10
4
OH ions are supplied to the NaOH solution and thus reducing the needed amount of IPA. Such type of supply of OH ions by the etchant solution is almost similar to that of the OH ions supplied by IPA. Moreover hydrazine monohydrate may be playing the role of reducing the interfacial energy of silicon/electrolyte in order to achieve sufficient wettability for the silicon surface. For this reason, we observed a good surface finish after texturization. Fig. 1 shows the surface morphology of a typical-texturized silicon surface using NaOH–N2H4, 2H2O system. From this surface morphology we have observed that uniform texturization throughout surface has been achieved even with lesser amount of IPA. Also, it is observed that the metal coverage on the front grid lines after Ag screen printing and firing is uniform throughout the contact region as shown in Fig. 4. This may be due to the less sharp pyramidal peak achieved after the NaOH–N2H4, 2H2O texturization (Fig. 1) compared to conventional NaOH textured silicon wafer (Fig. 2). This could be one of the causes for the high yield (more than 85% of fabricated solar cell with efficiency in the range 14–15%) in the industrial batch process as indicated in Fig. 5. This high yield is achieved even though the total reflectance of the present NaOH–N2H4, 2H2O bath texturized wafers is little bit
ARTICLE IN PRESS U. Gangopadhyay et al. / Solar Energy Materials & Solar Cells 90 (2006) 3094–3101
3099
Fig. 4. SEM picture of the front surface of the solar cell after screen-printed grid metallization followed by firing.
20
Number of Solar cells
18 16 14 12 10 8 6 4 2 0
13.6 13.8 14.0 14.2 14.4 14.6 14.8 15.0 Range of Efficiency(%)
Fig. 5. Yield percentage of batch process silicon solar cell.
lower than the conventionally NaOH texturized wafers as shown in Fig. 3. The high efficiency (greater than 14%) of the solar cells of the present study is due to the high values of the open circuit voltage(Voc), short circuit current (Isc), fill factor and the low value of the diode leakage current, respectively, as shown in Table 2. The squire’s nature of the illuminated I–V characteristic of the fabricated monocrystalline silicon solar cell
ARTICLE IN PRESS 3100
U. Gangopadhyay et al. / Solar Energy Materials & Solar Cells 90 (2006) 3094–3101
3.5
Current(A)
3.0 2.5
Sample ID : #NaH2
2.0
VOC Isc Vmax IMAX FF EFF
1.5 1.0 0.5 0.0 0.0
0.1
0.595V 3.399A 0.483V 3.052A 0.728 14.18%
0.2
0.3
0.4
0.5
0.6
0.7
Voltage(V) Fig. 6. Illuminated IV characteristics of the fabricated solar cell.
0.7
Spectral Response
0.6 0.5 0.4 0.3 0.2 0.1 0.0 400
600
800
1000
1200
Wavelength(nm) Fig. 7. Spectral response of the NaOH–N2H4, H2O texturized solar cell.
(Figs. 4–6) is responsible for the high fill factor (0.728). This factor supports the theory of the formation of a good metal coverage on the grid finger lines thereby ensuring a good metal contact. The spectral response of a typical NaOH–N2H4, 2H2O texturized silicon solar cell is shown in Fig. 7. The overall good spectral response is also the cause for the improvement of the efficiency of the cells of the present study. 4. Conclusion We have investigated the role of hydrazine monohydrate (N2H4, H2O) in NaOH texturization bath. A comparative study of the surface morphology and total reflectance of two different texturization approaches: (a) our novel low consumption IPA in NaOH–N2H4, H2O bath and (b) conventional NaOH texturization bath with comparatively higher IPA consumption have been performed. Monocrystalline silicon solar cells with more than 85% yield in the efficiency range of 14–15% have been fabricated. Our new approach is giving high hopes for the industrial production of high efficient solar cells.
ARTICLE IN PRESS U. Gangopadhyay et al. / Solar Energy Materials & Solar Cells 90 (2006) 3094–3101
3101
References [1] E.D. Palik, O.J. Glembocki, I. Heard Jr., P.S. Burno, L. Tenerz, J. Appl. Phys. 70 (1991) 3291. [2] Q.B. Vu, D.A. Stricker, P.M. Zavracky, J. Electrochem. Soc. 143 (1996) 1372. [3] R.A. Arndt, J.F. Allison, J.G. Haynos, A. Meulenberg, in: Proceedings of the 11th IEEE International Photovoltaic Specialists Conference, New York, 1975, p. 40. [4] P. Verlinden, O. Evrard, E. Muzy, A. Crahay, Sol. Energy Mater. Sol. Cells 26 (1992) 71. [5] S.R. Chitre, in: Proceedings of the 13th IEEE International Photovoltaic Specialist Conference, Washington DC, 1978, pp. 152–154. [6] D.L. King, M.E. Buck, in: Proceedings of the 22th IEEE International Photovoltaic Specialist Conference, Las Vegas, 1991, pp. 303–308. [7] P.M. Sarro, D. Bride, W.v.d. Vlist, S. Bride, Sens. Actuat. 85 (2000) 340. [8] R. Divan, N. Moldovan, H. Camon, Sens. Actuat. B 58 (1999) 438. [9] I. Zubel, M. Kramkowska, Sens. Actuat. A 93 (2001) 138.
Solar Energy Materials & Solar Cells 90 (2006) 3094–3101 www.elsevier.com/locate/solmat
Role of hydrazine monohydrate during texturization of large-area crystalline silicon solar cell fabrication U. Gangopadhyaya,b, Kyunghae Kimb, Ajoy Kandolb, Junsin Yib,, H. Sahaa a
IC Design and Fabrication Centre, Electronics and Tele-communication, Engineering Department, Jadavpur University, Kolkata 700032, India b School of Electrical and Computer Engineering, Sungkyunkwan University, 300 Chunchun-dong, Jangan-gu, Suwon 440-746, Republic of Korea Available online 24 July 2006
Abstract Reduction of optical losses in monocrystalline silicon solar cells by surface texturing is one of the important issues of modern silicon photovoltaic. For texturization during commercial monocrystalline silicon solar cell fabrication, a mixture of NaOH or KOH and isopropyl alcohol (IPA) is generally used in order to achieve good uniformity of pyramidal structure on the silicon surface. The interfacial energy between silicon and electrolyte should be reduced in order to achieve sufficient wettability for the silicon surface which in turn will enhance the pyramid nucleation. In this work, we have investigated the role of hydrazine monohydrate as a surface-active additive, which supplies OH ions after dissociation. This cuts down the IPA consumption during texturing without any loss of uniformity of textured pyramid. We are probably the first group to report such a novel idea of using hydrazine monohydrate addition in NaOH solution for texturization of solar cell. We were able to fabricate monocrystalline silicon solar cells with more than 85% yield in the range of 14–15% efficiency. r 2006 Elsevier B.V. All rights reserved. Keywords: Texturization; Hydrazine; IPA; Low cost; Silicon; Solar cell
Corresponding author. Tel.: +82 31 290 7139; fax: +82 31 290 7179.
E-mail address: [email protected] (J. Yi). 0927-0248/$ - see front matter r 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.solmat.2006.06.014
ARTICLE IN PRESS U. Gangopadhyay et al. / Solar Energy Materials & Solar Cells 90 (2006) 3094–3101
3095
1. Introduction Texturing of /1 0 0S oriented single crystal silicon substrates with appropriate antireflection coating (ARC) has become a well-established method in solar photovoltaic industry for minimizing the reflection loses. Many researchers [1,2] have shown the selective etching of /1 0 0S silicon by using sodium or potassium hydroxide solution. For monocrystalline silicon solar cells, anisotropic etch is used to form pyramidal structure that can collect the reflected light and trap the light inside the cells by internal reflection [3,4]. The most common etchant is the mixture of sodium hydroxide (NaOH) or potassium hydroxide (KOH) with water and isopropyl alcohol (IPA) [5,6]. In those etch solution, IPA can help not only to remove hydrogen bubbles but also to promote the formation of big pyramids. However, IPA easily pollutes the workshop and is expensive. Without IPA, NaOH solution does not always result in complete coverage of the surface with pyramids. One possible reason for this phenomenon is assumed to be an insufficient pyramid nucleation because of the poor wettability of silicon surface. The interfacial energy of silicon/electrolyte should be reduced in order to achieve sufficient wettability for the silicon surface which in turn can enhance the pyramidal nucleation. Mixing surface-active additives into the solution can reduce the interfacial energy [7,8]. IPA increases the wettability of the silicon surface but the rate of the silicon removal decreases strongly with increasing IPA concentration [9]. Hydrazine monohydrate was applied initially as the selective etchant for texturization. Normally higher temperature (490 1C) is selected during hydrazine selective texturization, because at that temperature hydrazine hydrate (N2H4, H2O) breaks in to ionized state and supply OH for texturization. In this paper, we report our investigation on the role of OH after ionization of hydrazine monohydrate in sodium hydroxide texturization solution. We have also reported the fabrication of high yield (485%) and high-efficiency (14–15%) monocrystalline silicon solar cells with this texturization approach. 2. Experimental 2.1. Texturization p-type /1 0 0S oriented monocrystalline silicon wafers with resistivity of about 1–5 O cm were used for the texturization. The etchant solution was heated using a heating plate and a flat polypropylene squire’s tub was used to cover the etchant vessel during etching to prevent the loss of chemical during texturization. The wafers were first dipped in a 8% NaOH solution at 75 1C for 2–3 min for damage etching followed by a dipping in the texturing bath. The concentrations of NaOH and hydrazine hydrate (1.8% and 4.3%, respectively) solutions were kept constant throughout the texturization process at a fixed bath temperature of 82 1C. The duration of the texturization was varied at four different values (Table 1). The etchant was not agitated during etching, because of the possibility of a detrimental effect on the characteristic reflectance of the textured samples. It was noticed that, after texturization using NaOH–N2H4, H2O texturization baths, all the wafers were equally textured without any spot on the surface. After texturing, the hemispherical surface reflectance was evaluated and compared with conventional NaOH texturized silicon surface, The surface morphology of the texturized
ARTICLE IN PRESS U. Gangopadhyay et al. / Solar Energy Materials & Solar Cells 90 (2006) 3094–3101
3096
Table 1 Experimental conditions adopted in the present study Batch Quantity NaOH no. of wafers conc. (%)
N2H4, H2O Time measured conc. (%) from the initial start of experiment (min)
Initial IPA conc. (%)
Additional IPA during each run (%)
Remarks
1
25
1.8
4.3
30
5
Nil
2
25
1.8
4.3
60
Nil
3.9
3
25
1.8
4.3
90
Nil
2.85
4
25
1.8
4.3
120
Nil
2.28
Uniform Texturization Uniform Texturization Uniform Texturization Uniform Texturization
silicon surface with two different methods (NaOH–N2H4, H2O and conventional NaOH) were also studied by scanning electron microscope (SEM). 2.2. Solar cell fabrication Monocrystalline silicon solar cells were fabricated using the conventional POCl3 diffusion, PECVD silicon nitride ARC and screen-printed metallization. All textured silicon wafers were diffused by n-type impurity in an open-tube furnace using conventional POCl3 diffusion source at 900 1C, with a 10 min pre-deposition followed by a 30 min drivein. After performing edge isolation, about 80 nm SiNx was deposited as an antireflection coating (ARC) at the front side of the wafer by means of PECVD at a temperature of 300 1C. The front and back metallization of the diffused texturized silicon wafers were carried out by screen printing technique using standard Al-paste (product no. FX 53-038, Ferro Electronic Materials) and Ag/Al paste (product no. 3398, Ferro Electronic Materials). This was followed by baking and co-firing at a temperature of 752 1C in a conveyer belt furnace. Back mesh structure has been used for the fabrication of the solar cells. Illuminated current–voltage (LIV) characteristic and spectral response (SR) studies of the fabricated monocrystalline solar cells were carried out and the results are presented. 3. Results and discussion From the different experimental conditions depicted in Table 1, it is observed that the amount of IPA added during each successive batch of texturization process has been reduced from 5% (first batch run) to 2.23% (fourth batch run) without any bubble spot on the texturized silicon wafers. The good surface finish of the texturized silicon even with low amount of IPA may be due to the dissociation of hydrazine hydrate leading to the supply OH ions to the NaOH bath. Actually, during the initial stages of experiment carried out with the first lot of wafers, the hydrazine monohydrate in the NaOH solution did not dissociate at the temperature of 82 1C, because it took longer time to dissociate at that temperature. With the increase of time, more hydrazine is dissociated and hence more
U. Gangopadhyay et al. / Solar Energy Materials & Solar Cells 90 (2006) 3094–3101
3097
Fig. 1. SEM picture of a typical texturized silicon surface using NaOH–N2H4, H2O texturization bath.
Fig. 2. SEM picture of a typical texturized silicon surface using conventional NaOH texturization bath.
ARTICLE IN PRESS 3098
U. Gangopadhyay et al. / Solar Energy Materials & Solar Cells 90 (2006) 3094–3101
14
Total Reflectance
12 10 8 6 4 2 0 NaOH-N2H4,H2O
NaOH
Texturized Bath Fig. 3. Total reflectance of texturized silicon surface using NaOH–N2H4, H2O and conventional NaOH texturization baths, respectively.
Table 2 Electrical parameters of NaOH–N2H4, H2O texturized monocrystalline silicon solar cells Description of texturization bath
Voc (V)
Isc (A)
Pm (W)
FF
Efficiency (%)
Rs (m O)
Rsh (O)
I01 (A)
New NaOH– N2H4, H2O bath
0.595
3.399
1.47
0.73
14.18
21
125.40
4.13 10
I02 (A) 8
1.23 10
4
OH ions are supplied to the NaOH solution and thus reducing the needed amount of IPA. Such type of supply of OH ions by the etchant solution is almost similar to that of the OH ions supplied by IPA. Moreover hydrazine monohydrate may be playing the role of reducing the interfacial energy of silicon/electrolyte in order to achieve sufficient wettability for the silicon surface. For this reason, we observed a good surface finish after texturization. Fig. 1 shows the surface morphology of a typical-texturized silicon surface using NaOH–N2H4, 2H2O system. From this surface morphology we have observed that uniform texturization throughout surface has been achieved even with lesser amount of IPA. Also, it is observed that the metal coverage on the front grid lines after Ag screen printing and firing is uniform throughout the contact region as shown in Fig. 4. This may be due to the less sharp pyramidal peak achieved after the NaOH–N2H4, 2H2O texturization (Fig. 1) compared to conventional NaOH textured silicon wafer (Fig. 2). This could be one of the causes for the high yield (more than 85% of fabricated solar cell with efficiency in the range 14–15%) in the industrial batch process as indicated in Fig. 5. This high yield is achieved even though the total reflectance of the present NaOH–N2H4, 2H2O bath texturized wafers is little bit
ARTICLE IN PRESS U. Gangopadhyay et al. / Solar Energy Materials & Solar Cells 90 (2006) 3094–3101
3099
Fig. 4. SEM picture of the front surface of the solar cell after screen-printed grid metallization followed by firing.
20
Number of Solar cells
18 16 14 12 10 8 6 4 2 0
13.6 13.8 14.0 14.2 14.4 14.6 14.8 15.0 Range of Efficiency(%)
Fig. 5. Yield percentage of batch process silicon solar cell.
lower than the conventionally NaOH texturized wafers as shown in Fig. 3. The high efficiency (greater than 14%) of the solar cells of the present study is due to the high values of the open circuit voltage(Voc), short circuit current (Isc), fill factor and the low value of the diode leakage current, respectively, as shown in Table 2. The squire’s nature of the illuminated I–V characteristic of the fabricated monocrystalline silicon solar cell
ARTICLE IN PRESS 3100
U. Gangopadhyay et al. / Solar Energy Materials & Solar Cells 90 (2006) 3094–3101
3.5
Current(A)
3.0 2.5
Sample ID : #NaH2
2.0
VOC Isc Vmax IMAX FF EFF
1.5 1.0 0.5 0.0 0.0
0.1
0.595V 3.399A 0.483V 3.052A 0.728 14.18%
0.2
0.3
0.4
0.5
0.6
0.7
Voltage(V) Fig. 6. Illuminated IV characteristics of the fabricated solar cell.
0.7
Spectral Response
0.6 0.5 0.4 0.3 0.2 0.1 0.0 400
600
800
1000
1200
Wavelength(nm) Fig. 7. Spectral response of the NaOH–N2H4, H2O texturized solar cell.
(Figs. 4–6) is responsible for the high fill factor (0.728). This factor supports the theory of the formation of a good metal coverage on the grid finger lines thereby ensuring a good metal contact. The spectral response of a typical NaOH–N2H4, 2H2O texturized silicon solar cell is shown in Fig. 7. The overall good spectral response is also the cause for the improvement of the efficiency of the cells of the present study. 4. Conclusion We have investigated the role of hydrazine monohydrate (N2H4, H2O) in NaOH texturization bath. A comparative study of the surface morphology and total reflectance of two different texturization approaches: (a) our novel low consumption IPA in NaOH–N2H4, H2O bath and (b) conventional NaOH texturization bath with comparatively higher IPA consumption have been performed. Monocrystalline silicon solar cells with more than 85% yield in the efficiency range of 14–15% have been fabricated. Our new approach is giving high hopes for the industrial production of high efficient solar cells.
ARTICLE IN PRESS U. Gangopadhyay et al. / Solar Energy Materials & Solar Cells 90 (2006) 3094–3101
3101
References [1] E.D. Palik, O.J. Glembocki, I. Heard Jr., P.S. Burno, L. Tenerz, J. Appl. Phys. 70 (1991) 3291. [2] Q.B. Vu, D.A. Stricker, P.M. Zavracky, J. Electrochem. Soc. 143 (1996) 1372. [3] R.A. Arndt, J.F. Allison, J.G. Haynos, A. Meulenberg, in: Proceedings of the 11th IEEE International Photovoltaic Specialists Conference, New York, 1975, p. 40. [4] P. Verlinden, O. Evrard, E. Muzy, A. Crahay, Sol. Energy Mater. Sol. Cells 26 (1992) 71. [5] S.R. Chitre, in: Proceedings of the 13th IEEE International Photovoltaic Specialist Conference, Washington DC, 1978, pp. 152–154. [6] D.L. King, M.E. Buck, in: Proceedings of the 22th IEEE International Photovoltaic Specialist Conference, Las Vegas, 1991, pp. 303–308. [7] P.M. Sarro, D. Bride, W.v.d. Vlist, S. Bride, Sens. Actuat. 85 (2000) 340. [8] R. Divan, N. Moldovan, H. Camon, Sens. Actuat. B 58 (1999) 438. [9] I. Zubel, M. Kramkowska, Sens. Actuat. A 93 (2001) 138.