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p/i(nc-Si:Hx/a-Si:Hy multilayers)/n solar cells prepared by periodical switching RF plasma
本論文實驗為使用射頻13.56 MHz脈波調變電漿輔助化學氣相沉積 (Pulsed-PECVD) 技術，以改變射頻功率、氫稀釋比與壓力製作氫化奈米矽與氫化非晶矽薄膜。藉由週期性變化射頻電漿狀態製作nc-Si:Hx/a-Si:Hy多層膜，及氫電漿處理奈米矽子層界面，最後將多層膜應用在太陽電池的本質層，探討其對太陽電池特性的影響。
In this thesis, 13.56 MHz plasma-enhanced chemical vapor deposition (Pulsed-PECVD) with pulse modulation of RF plasma is used to fabricate hydrogenated nano-crystal silicon (nc-Si:H) and hydrogenated amorphous silicon (a-Si:H) films by changing RF power, hydrogen dilution and pressure. The nc-Si:Hx/a-Si:Hy multilayers were fabricated by periodically changing RF plasma conditions, and hydrogen plasma was used to treat the interfaces of nc-Si:Hx sublayers. These multilayers are used as the i-layer of the solar cells to explore how multilayers influence the characteristics of solar cells.
The deposition rate, optical properties of bandgap (Eg), refractive index (n) and dielectric constants (ε1 and ε2) were measured by spectroscopic ellipsometry (SE). The surface roughness of the films was measured by atomic force microscope (AFM), and the periodical structures of nc-Si:Hx/a-Si:Hy multilayers were measured by X-ray diffraction (XRD). The photo, dark current and the electro-optical characteristics of solar cells were obtained through I-V system.
For single a-Si:H layers, increasing plasma power, hydrogen dilution and reducing the pressure of deposition can induce the growth of silicon nanoparticles and increase the density of nanoparticles in the nc-Si:H films. Increasing H2 treatment time, the interfaces of multilayers were passivated and became smooth.
From the I-V characteristics of single and multilayer i-layers of solar cells, the C_3t cell with a single i-layer deposited at 3 torr has high efficiency than those of multilayer i-layers of solar cells. It is due to that there are no many interfaces of sublayers, the recombination of photogenerated carriers in the i-layer is small, thus the short-circuit current and efficiency are higher than those of multilayer i-layers of solar cells. For multilayer i-layers of solar cells, the short-circuit current, fill factor and efficiency of solar cells can be increased by suitable pulse modulation of H2 plasma treatment to passivate the defects at the interfaces between the sublayers. Hydrogen plasma treatment can improve the quality of the interfaces of the multilayers and increase the efficiency of solar cells.
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