| Summary: | 碩士 === 國立中興大學 === 電機工程學系所 === 98 === In this thesis, 13.56 MHz plasma-enhanced chemical vapor deposition (PECVD) with pulse modulation of RF plasma is used to fabricate the single-layer, hydrogenated protocrystal silicon/hydrogenated amorphous silicon (pc-Si:H/a-Si:H) multilayer and graded-layer intrinsic films of p-i-n silicon thin film solar cells by constant, periodic and gradual variation of the hydrogen dilution ratio (R = H2/SiH4).
Single-layer intrinsic films are deposited by R change from 4 to 28 and fixed the thickness at 300 nm. Pc-Si:H/a-Si:H multilayer intrinsic films are fabricated with R from 6 to 28 for pc-Si:H as A sublayers (fixed at 20 nm), and with R = 4 for a-Si:H as the B sublayers (fixed at 10 nm). The total thickness of the pc-Si:H/a-Si:H multilayer intrinsic film is 300 nm with a period of 30 nm and 10 periods. The a-Si:H to pc-Si:H (or pc-Si:H to a-Si:H) graded-layer intrinsic films are fabricated by gradually change the hydrogen dilution ratio from R = 4 to 28 or R = 28 to 4.
The optical band gap of single-layer films is increased, but the absorption coefficient and the film density are decreased as the hydrogen dilution ratio is increased. For pc-Si:H/a-Si:H multilayer films, absorption coefficient and film density are decreased due to the increasing of pc-Si:H layer hydrogen dilution ratio, and the structures gradually change to protocrystal structure.
The short-circuit current density, fill factor and energy conversion efficiency of single-layer and pc-Si:H/a-Si:H multilayer intrinsic films solar cells are decreased due to the increasing of hydrogen dilution ratio. For the graded-layer intrinsic film solar cells, increasing the number of grading layers and the total thickness of i-layer can increase the short-circuit current density and the energy conversion efficiency.
Single-layer intrinsic film solar cells have high energy conversion, but low stability. The pc-Si:H/a-Si:H multilayer intrinsic film solar cells have high stability. The energy conversion efficiency of graded-layer intrinsic film solar cells are between those of single-layer and pc-Si:H/a-Si:H multilayer intrinsic film solar cell, but its stability compared with single-layer film solar cell is significantly improved. In conclusion, pc-Si:H/a-Si:H multilayer and graded intrinsic films structures can improve the stability of solar cells.
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