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

CuInSe_2 （CIS）是一种很有前途的高效薄膜太阳能电池材料。采用CDS/CIS异质结的太阳能电池存在Cd在CDS中的污染问题。本文研究了无污染的SnO_2/CIS异质结的制备及其表征。一般来说，热气相沉积法在温度高于550℃时形成SnO_2薄膜，因此在CIS上沉积SnO_2的过程中会发生CIS薄膜的劣化。因此，我们对SnO_2薄膜的等离子体CVD生长进行了研究，以期实现SnO_2薄膜的低温生长。等离子体气相沉积装置采用市售等离子体腔，配以射频功率发生器、匹配电路和进气系统。将含锡饱和的氩气（TBT）与氧气一起送入反应器。沉积压力为1torr。采用玻璃基板。测定了生长条件（电极间距、射频功率、衬底温度、TBT温度、氧流量）对SnO_2薄膜厚度、x射线图、透射率、电子浓度和迁移率的影响。在衬底温度350ºC，射频功率80w， TBT温度140ºC，氩气流量120 ml/min，氧气流量100 ml/min的条件下，生长出了质量较好的多晶薄膜。没有射频功率就没有胶片生长。这表明等离子体对薄膜的生长起着重要的作用。在此基础上，制备了SnO_2/CIS异质结二极管。这个二极管显示出整流特性。然而，没有观察到光电压。这可能是由于CVD开始时CIS表面氧化所致。我们计划克服这一问题，并继续研究具有ITO、ZnO和a-Si异质结的CIS太阳能电池。

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.