Study on New Heterojunction in CIS (CuInSe_2) Thin Film Solar Cells

1991 Fiscal Year Final Research Report Summary

• Project/Area Number: 02650227
• Research Category: Grant-in-Aid for General Scientific Research (C)
• Allocation Type: Single-year Grants
• Research Field: 電子材料工学
• Research Institution: Ehime University
• Principal Investigator: ISOMURA Shigehiro Ehime Univ., Faculty of Engineering, Professor, 工学部, 教授 (00116906)
• Co-Investigator(Kenkyū-buntansha): SHINOHARA Kazumitsu Ehime Univ., Faculty of Engineering, Professor, 工学部, 教授 (40036497) ; SHIRAKATA Sho Ehime Univ., Faculty of Engineering, Research Associate, 工学部, 助手 (10196610)
• Project Period (FY): 1990 – 1991
• Keywords: CuInSe_2 thin film solar cell / SnO_2 thin film / plasma CVD / heterojunction

Research Abstract

CuInSe_2 (CIS) is a promising material for efficient thin film solar cell. The solar cell using the CDS/CIS heterojunction has the Pollution problem of Cd in CdS. In this research, the preparation of pollution free SnO_2/CIS hererojunctions and its characterization have been done.
In general, the SnO_2 films are formed at temperature higher than 550 C by thermal CVD, and therefore the deterioration of CIS films occur during the deposition of SnO_2 on CIS. This reason Iets us study the plasma CVD growth of SnO_2 films, by which method low temperature growth of SnO_2 films expected.
The plasma CVD apparatus was constructed using the commercially available plasma chamber with the RF power generator, matching circuit and gas inlet system.
As the source materials, Ar gas saturated with the tin (TBT) was fed to the reactor together with oxygen. The deposition pressure was 1 Torr. Glass substrate was used. The dependences of the characteristics of SnO_2 (film thickness, X-ray pattern, transmittance, electron concentration and mobility) on the growth conditions (distance between electrode, RF power, substrate temperature, TBT temperature, oxygen flow rate) have been determined. The good quality polycrystalline films were grown under the conditions of substrate temperature of 350ﾟC, RF power of80W, TBT temperature of 140ﾟC, Ar flow rate of 120 ml/min and oxygen flow rate of 100 ml/min. No film was grown without RF power. This indicates that the plasma plays an important role for the film growth.
Based on this result, SnO_2/CIS heterojunction diode has been prepared. This diode exhibited a rectifying characteristic. However, no photovoltage was observed. This may be due to the oxidation of the surface of CIS at the beginning of the CVD. We plan to overcome this problem and to continue the research of the CIS solar cells havinig the heterojunction with ITO, ZnO and a-Si.