Browsing by Author "Sai, Hitoshi"

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Application of Porous a-Si:H Passivation Layer Deposited Using Si2H6 Precursor in Silicon Heterojunction Solar Cells
(2018-01-01)
Chen, Po-Wei
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Chen, Pei-Ling
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Hsu, Hung-Jung
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Matsui, Takuya
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Sai, Hitoshi
The improved silicon heterojunction solar cell efficiency by employing porous a-Si:H passivation layer deposited using Si2H6 precursor is presented. By introducing Si2H6 precursor into the commonly-used SiH4 plasma, it is demonstrated that the porosity of a-Si:H passivation layer can be increased significantly. A stack of the porous a-Si:H passivation layer with overlying dense a-Si:H capping layer preserves excellent interface passivation even after doped layer deposition. In the finished solar cell, improvements in Voc from 0.691 to 0.714 V and efficiency from 20.0 to 21.0% were obtained as a consequence of using porous a-Si:H passivation layer deposited under high Si2H6 concentration.
Impact of intrinsic amorphous silicon bilayers in silicon heterojunction solar cells
(2018-09-14)
Sai, Hitoshi
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Chen, Po-Wei
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Hsu, Hung-Jung
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Matsui, Takuya
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Nunomura, Shota
The impact of intrinsic amorphous silicon bilayers in amorphous silicon/crystalline silicon (a-Si:H/ c-Si) heterojunction solar cells is investigated. The microstructure factor R* of the interfacial a-Si: H layer, which is related to the Si-H bond microstructure and determined by infrared absorption spectroscopy, is controlled in a wide range by varying the growth pressure and the power density in plasma-enhanced chemical vapor deposition process. Surface passivation at the a-Si:H/c-Si interface is significantly improved by using an intrinsic a-Si:H bilayer, i.e., a stack of an interfacial layer with a large R* and an additional dense layer, particularly after the deposition of an overlying p-type a-Si:H layer. Consequently, the conversion efficiency of a-Si:H/c-Si heterojunction solar cells is markedly increased. However, it is also revealed that such an interfacial layer causes some negative effects including the increase in the series resistance and the current loss at the front side, depending on the growth condition. This result indicates that the interfacial layer has a significant impact on both the majority and the minority carrier transport. Thus, R* of the interfacial layer is an important parameter for obtaining good surface passivation at the a-Si/c-Si interface, but not the sole parameter determining the conversion efficiency of a-Si:H/c-Si heterojunction solar cells. Published by AIP Publishing.
Investigation of P-type Hydrogenated Nanocrystalline Silicon Grown by VHF-PECVD as Emitter in Silicon Heterojunction Solar Cells
(2018-01-01)
Chen, Pei-Ling
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Chen, Po-Wei
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Matsui, Takuya
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Sai, Hitoshi
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Tsai, Chuang-Chuang
P-type hydrogenated nanocrystalline silicon (ncSi: H(p)) films as emitter layers in silicon heterojunction solar (SHJ) cells by VHF-PECVD (65 and 100 MHz) and standard RF-PECVD (13.56 MHz) were investigated. We demonstrate that the use of VHF-PECVD is advantageous in fast nucleation in a very thin layer (< 15 nm), which in turn results in improved TCO/p contact. In addition, the deposition of nc-Si: H (p) layer by VHF-PECVD can improve the surface passivation properties as evidenced by QSSPC lifetime measurement for the solar cell precursor (i. e., pi/ c-Si/ in). These results suggest that VHF plasma generates more atomic hydrogen flux, which brings beneficial aspects both in terms of nc-Si: H growth and post-hydrogenation. Compared to our standard a-Si: H(p) emitter, the use of nc-Si: H(p) prepared by 65 MHz PECVD improved the efficiency from 19.59% to 20.50%.