成果報告書詳細
管理番号20120000000155
タイトル*平成23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(強相関材料)
公開日2012/6/20
報告書年度2011 - 2011
委託先名理化学研究所
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:Strongly correlated electron materials

The aim of this research project is to verify the possibility of generating multiple carriers by single high energy photon excitation in correlated electron oxides and extracting these carriers as photocurrent by the internal electric field in heterojunction. Multiple carrier generation is one of the most challenging and promising routes to accomplish substantially high efficiency in future photovoltaics. However, current research is focused on pump-probe experiments using narrow band gap semiconductor nano-particles dispersed in liquid as a colloidal solution to detect multiple exciton generation. This unrealistic system has to be chosen because semiconductor has very low electron correlation. Yet the possibility is unknown, we would like to make use of strong electron correlation in transition metal oxides.
As the research in FY H-23, we set the following research targets and have obtained respective results.
(1) We have developed an application program to simulate a solar-cell action in correlated electron materials. This year, we improved the program to make it possible to simulate the process of the photocarrier generation in heterojunctions with including in the model system the electron spin interaction and realistic band structure. Using this program, we revealed that a heterojunction composed of two different correlated electron materials shows multiple photocarrier generation, and the yield reaches up to 250 % by the excitation of photons having a triple energy of the band gap.
(2) Last year, we reported the photovoltaic effect in Mott-insulator/Nb:SrTiO3 heterojunctions. There, the effective thickness for the photocurrent generation, i.e., the total width of depletion layer and diffusion length was estimated to be about 6 nm. This year, we controlled the depletion layer width by applying an external electric field to the junction and analyzed the change in the amplitude of the photocurrent. By this measurement, we verified the existence of depletion layer in a Mott insulator LaMnO3 and the width of it is about 3 nm. This knowledge gives us a guide to design the solar cells.
(3) As another candidate of solar cell material, we examined x-ray irradiation effect on W doped VO2 (W:VO2) thin film. The conductivity of the film drastically increased during the irradiation of x-ray and was stable even after stopping the irradiation, indicating that this is a persistent transition. We found that one x-ray photon can induce the insulator-metal transition at large number of atomic sites and the yield reaches up to 105. We will extend this study to examine the multiple carrier generation with use of visible light.
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