2004 Fiscal Year Final Research Report Summary
Optimal fabrication processes for high-efficiency chalcopyrite thin-film solar-cells
| Project/Area Number |
14350161
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| Research Category |
Grant-in-Aid for Scientific Research (B)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
Electronic materials/Electric materials
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| Research Institution | Faculty of Engineering, Shinshu University |
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Principal Investigator |
ITO Kentaro Shinshu University, Electrical and Electronic Engineering Department, Professor, 工学部, 教授 (20020977)
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| Co-Investigator(Kenkyū-buntansha) |
HASHIMOTO Yoshio Shinshu University, Electrical and Electronic Engineering, Associate Professor, 工学部, 助教授 (30262687)
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| Project Period (FY) |
2002 – 2004
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| Keywords | thin film / solar cell / chalcopyrite / conversion efficiency / precursor / sulfurization / film adhesion / short circuit curent |
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| Research Abstract |
The purpose of the present research work is to improve the performance of a chalcopyrite thin-film solar cell and the adhesion of the film to a Mo-coated soda lime glass substrate. The results of our investigation are summarized as follows.
In the first step of sulfurization, we prepared a CuGaS_2 thin film on the substrate, where the Cu to Ga ratio of a vacuum-evaporated metallic precursor was equal to 1.0. In the second step, an optical absorber layer of CulnS_2 was prepared on it by sulfurization of a stacked precursor layer consisting of Cu/In. The Cu to In ratio was varied from 1.3 to 2.3. When the ratio is larger than 1.7, the cell exhibited a large short-circuit current density. This is considered to be due to the presence of Cu_xS quantum dots formed in the absorber layer. Solar cells with efficiency up to 11% was obtained using a Cu to In ratio between 1.7 and 2.1.
Using a precursor consisting of vacuum-evaporated GaS, In and Cu, we prepared a Cu(In,Ga)S_2 thin film. A high efficiency solar cell was obtained with the GaS thickness of 40nm and the Cu/In ratio of 1.2. When the GaS is made thicker, inhomogeneous distribution of In prevails, eventually leading to an inefficient solar cell. The performance of the best cell was as follows : open circuit voltage is 673mV, short circuit current density 22.7mA/cm2, fill factor 0.61 and efficiency 10.8%.
Adhesion of the chalcopyrite film to the substrate was improved by incorporation of Al into the absorber layer. Even if the Cu/(In+Al) ratio of a sputtered metallic precursor is increased to 2.7, peeling of the film was not observed. A CuAlS_2 thin layer was obtained by sulfurization in a closed quartz ampoule as a first chalcopyrite, The layer exhibited p-type conductivity, resistivity higher than 60 Ωcm and energy bandgap of 3.5eV.
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