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P-type hydrogenated silicon oxide (p-SiOx:H) films are prepared by radio frequency plasma enhanced chemical deposition with various CO2 flow rates. We use gas mixtures of carbon dioxide (CO2), hydrogen (H2), silane (SiH4) and diborane (B2H6) as reaction source gases. For all experiments the substrate temperature, pressure and power density are fixed at 200 oC, 200 Pa and 200 mW/cm2, respectively. The films are deposited on Corning Eagle 2000 glass substrates for optoelectronic measurements and on crystalline Si wafers for Fourier transform infrared (FTIR) measurement. The structural, optical and electronic properties of the films are systematically studied as a function of CO2 flow rate. The CO2 flow rate is varied from 0 to 1.2 cm3 min-1, with all other parameters kept constant. It is shown that with the CO2 flow rate increasing from 0 to 1.2 cm3 min-1, the Raman peak shifts from 520 cm-1 to 480 cm-1 and corresponding crystalline volume fraction decreases from 70% to 0. In addition, the FTIR spectrum shows that the oxygen content increases from 0 to 17% and the hydrogen bond configuration gradually shifts from mono-hydrogen (Si-H) to di-hydrogen (Si-H2) and (Si-H2)n complexes in the film. What is more, with the incorporation of oxygen, the optical band gap of each of all p-type SiO:H films increases from 1.8 eV to 2.13 eV, while the dark conductivity decreases from 3 S/cm (nc-Si:H phase) to 8.310-6 S/cm (a-SiOx:H phase). Furthermore, the oxygen incorporation tends to disrupt the growth of silicon nanocrystals due to the created dangling bonds that arises from an increased structural disorder. This leads to microstructural evolution of SiO:H film from a single nanocrystalline phase into first a mixed amorphous-nanocrystalline and subsequently into an amorphous phase. At a certain threshold of CO2 flow rate, a transition from nanocrystalline to amorphous growth takes place. The transition from nanocrystalline to amorphous silicon is confirmed by Raman and FTIR spectra. In the transition region or crystalline volume fraction of about 45%, Raman spectrum also reveals that the a mixture of nanocrystalline silicon and amorphous silicon oxide (a-SiOx:H) phase exists in the film. This means that nanocrystalline silicon oxide (nc-SiO:H) is a two-phase structural material consisting of a dispersion of silicon nanocrystals (nc-Si) embedded in the amorphous SiOx network. As is well known, the oxygen-rich amorphous phase can help enhance the optical band gap, while the nc-Si phase contributes to high conductivity. Finally, it is the SiO:H film deposited at phase transition that can realize a relatively high dark conductivity (about S/cm) with a wide optical band gap of 2.01 eV in the film. By using the transition p-layer as the window layer in conjunction with a suitable buffer thickness, we obtain a thin film solar cell with an open-circuit voltage of 890 mV, a short-circuit current density of 12.77 mAcm-2, fill factor of 0.73, and efficiency of 8.27% without using any back reflector.
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Keywords:
- radio-frequency plasma enhanced chemical vapor deposition /
- transition p layer /
- SiO:H films /
- optical band gap
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[4] Kobsak S, Nopphadol S, Puchong S 2011 Curr. Appl. Phys. 11 S47
[5] Matsumoto Y, Mele Hndez F, Asomoza R 2001 Sol. Energy Mater. Sol. Cells 66 163
[6] Yoon K, Kim Y, Park J, Shin C H, Baek S, Jang J, Iftiquar S M, Yi J 2011 J. Non-Cryst. Solids 357 2826
[7] Liu H X, Yang Y B, Liu J P, Jiang Z Y, Yu W, Fu G S 2016 J. Alloys Compod. 671 532
[8] Liao X B, Du W H 2006 J. Non-Cryst. Solids 352 1841
[9] Yue G, Lorentzen J D, Lin J, Wang Q, Han D 1999 Appl. Phys. Lett. 75 492
[10] Arup S, Debajyoti D 2009 Sol. Energy Mater. Sol. Cells 93 588
[11] Iftiquar S M 1998 J. Phys. D:Appl. Phys. 31 1630
[12] Haga K, Watanabe H 1996 J. Non-Cryst. Solids 195 72
[13] He L, Inokuma T, Kurata Y, Hasegawa S 1995 J. Non-Cryst. Solids 185 249
[14] Lucovsky G, Yang J, Chao S S, Tyler J E, Czubatyj W 1983 Phys. Rev. B 283 225
[15] Kichan Y, Youngkuk K, JinJoo P J 2011 J. Non-Cryst. Solids 357 2826
[16] Daey Ouwens J, Schropp R E I 1996 Phys. Rev. B 177 59
[17] Dalal V, Knox R, Moradi B 1993 Sol. Energy Mater. Sol. Cells 31 349
[18] Chang T H, Chang J Y, Chu Y H 2013 Surf. Coat. Technol. 231 604
[19] Yang L, Abeles B, Eberhardt W, Sondericker D 1989 IEEE Trans. Electron Dev. 36 2798
[20] Mahan A H, Nelson B P, Salamon S, Crandall R S 1991 J. Non-Cryst. Solids 137 657
[21] Wang S, Wang Q, Zhang X D 2012 Proceedings of the 12th China PV Conference Beijing, September 2-7, 2012 p163
[22] Buehlmann P, Bailat J, Domin D, Billet A, Meillaud F, Feltrin A, Ballif C 2007 Appl. Phys. Lett. 143 505
[23] Zhang S B, Liao X B, An L, Kong G L, Wang Y Q 2002 Acta Phys. Sin. 51 1811 (in Chinese)[张世斌, 廖显伯, 安龙, 孔光临, 王永谦 2002 51 1811]
[24] Qiao Z, Xie X J, Hao Q Y, Wen D, Xue J M, Liu C C 2015 Appl. Surf. Sci. 324 152
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[1] Lambertz A, Finger F, Hollnder B, Rath J K, Schropp R E 2012 J. Non-Cryst. Solids 358 1962
[2] Zacharias M, Freistedt H, Stolze F 1993 J. Non-Cryst. Solids 164 1089
[3] Naka yama Y M, Uecha T, Ikeda M 1996 J. Non-Cryst. Solids 198 915
[4] Kobsak S, Nopphadol S, Puchong S 2011 Curr. Appl. Phys. 11 S47
[5] Matsumoto Y, Mele Hndez F, Asomoza R 2001 Sol. Energy Mater. Sol. Cells 66 163
[6] Yoon K, Kim Y, Park J, Shin C H, Baek S, Jang J, Iftiquar S M, Yi J 2011 J. Non-Cryst. Solids 357 2826
[7] Liu H X, Yang Y B, Liu J P, Jiang Z Y, Yu W, Fu G S 2016 J. Alloys Compod. 671 532
[8] Liao X B, Du W H 2006 J. Non-Cryst. Solids 352 1841
[9] Yue G, Lorentzen J D, Lin J, Wang Q, Han D 1999 Appl. Phys. Lett. 75 492
[10] Arup S, Debajyoti D 2009 Sol. Energy Mater. Sol. Cells 93 588
[11] Iftiquar S M 1998 J. Phys. D:Appl. Phys. 31 1630
[12] Haga K, Watanabe H 1996 J. Non-Cryst. Solids 195 72
[13] He L, Inokuma T, Kurata Y, Hasegawa S 1995 J. Non-Cryst. Solids 185 249
[14] Lucovsky G, Yang J, Chao S S, Tyler J E, Czubatyj W 1983 Phys. Rev. B 283 225
[15] Kichan Y, Youngkuk K, JinJoo P J 2011 J. Non-Cryst. Solids 357 2826
[16] Daey Ouwens J, Schropp R E I 1996 Phys. Rev. B 177 59
[17] Dalal V, Knox R, Moradi B 1993 Sol. Energy Mater. Sol. Cells 31 349
[18] Chang T H, Chang J Y, Chu Y H 2013 Surf. Coat. Technol. 231 604
[19] Yang L, Abeles B, Eberhardt W, Sondericker D 1989 IEEE Trans. Electron Dev. 36 2798
[20] Mahan A H, Nelson B P, Salamon S, Crandall R S 1991 J. Non-Cryst. Solids 137 657
[21] Wang S, Wang Q, Zhang X D 2012 Proceedings of the 12th China PV Conference Beijing, September 2-7, 2012 p163
[22] Buehlmann P, Bailat J, Domin D, Billet A, Meillaud F, Feltrin A, Ballif C 2007 Appl. Phys. Lett. 143 505
[23] Zhang S B, Liao X B, An L, Kong G L, Wang Y Q 2002 Acta Phys. Sin. 51 1811 (in Chinese)[张世斌, 廖显伯, 安龙, 孔光临, 王永谦 2002 51 1811]
[24] Qiao Z, Xie X J, Hao Q Y, Wen D, Xue J M, Liu C C 2015 Appl. Surf. Sci. 324 152
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