成果報告書詳細
管理番号20130000000133
タイトル*平成24年度中間年報 新エネルギー技術研究開発 革新的太陽光発電技術研究開発(革新型太陽電池国際研究拠点整備事業)高度秩序構造を有する薄膜多接合太陽電池の研究開発(フッ素系イオン制御プロセス、pn接合内蔵CNT)
公開日2013/10/25
報告書年度2012 - 2012
委託先名国立大学法人東北大学
プロジェクト番号P07015
部署名新エネルギー部
和文要約
英文要約Title: Exploring multi-junction thin-film solar cells with highly ordered structures (pn-junction embedded carbon nanotube) (FY2008-2014) FY2012 Annual Report

Single-walled carbon nanotubes (SWNTs) are quasi one-dimensional materials exhibiting interesting electrical and optical properties, and their semiconducting properties can be controlled by the encapsulation of the other materials, which makes them promising candidates for fabrication of solar cells.
In our previous work, the possibility of making infrared solar cells based on p-n junction embedded SWNT (pristine p-type SWNT and cesium (Cs) encapsulated n-type SWNT) has been systematically investigated. It is found that the p-n junction embedded SWNT generates photovoltaic power under the infrared light irradiation and the energy conversion efficiency is larger than 2%, which is attributed to the utilization of the high mobility of SWNTs along the axis. However, the short circuit current of p-n junction embedded SWNT is very small, because only one SWNT works as a conducting channel between two electrodes.
Since the channel area of p-n junction embedded SWNT should be proportional to the number of SWNTs, the solar cell performance is expected to be improved by increasing the number of SWNTs between two electrodes. Thus, we attempt to fabricate multi-channel p-n junction embedded SWNTs solar cell using SWNTs films. To fabricate the high performance solar cell with SWNTs films, there are several issues to be overcome. First, it is necessary to decrease the concentration of metallic SWNTs as low as possible. Second, controllable carrier doping technique should be established to create clear p-n junction structures. The first issue is solved by using highly semiconductor-enriched SWNTs (99%) as a starting material. It is confirmed that the performance of SWNTs-thin film transistor (TFTs) can be improved by using the semiconductor-enriched SWNTs. The averaged on/off ratio is over 1000, which is almost two order higher than that of pristine SWNTs-TFTs. To approach the second issue, we attempt to realize the position controlled doping of Cs ions by combining our plasma ion irradiation technique with the conventional photolithography processing. Prior to the Cs irradiation, the half part of SWNTs channel is covered by a polymer film, which prevents Cs atoms from being encapsulated into SWNTs. Through the detailed measurements of electrical transport properties, clear rectifying features are often observed for the position selectively Cs doped SWNTs-TFTs. This indicates that p-n junction structures should be successfully formed in the channel made of SWNTs thin films. The systematic investigations also uncover that the Cs encapsulated SWNTs are very stable under the various environments such as air, water, and high temperature conditions (< 400 ℃). This very stable n-type SWNTs-TFTs should be important for the practical application as solar cell devices. The detailed solar cell properties of p-n junction embedded SWNTs-TFTs will be evaluated in next year.
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