Study on the Buffer Layer of CIS Thin Film Solar Cell by Separate-Melting Chemical Bath Deposition Methods

In this work, cadmium sulphide (CdS) buffer layer of CuInSe2 (CIS) thin film solar cell is fabricated by separate-melting Chemical Bath Deposition (CBD) methods. The reason of adopting the CdS thin film as the buffer layer of CIS thin film solar cell is that the CdS can act as energy gap buffer and reduce the band-offset between CIS absorbing layer and the Transparent Conductive Oxide layer. The CdS thin films are generated by the separate-melting CBD methods in situation of atmosphere. In order to analyze the characteristics of the CdS thin films conveniently, the CdS thin films are firstly fabricated on Soda-lime, and the final found optimal CdS thin film is fabricated on the CIS/Mo/Soda-lime glasses. Then the p-n diode characteristic of the CdS/CIS/Mo/Soda-lime glasses is measured by four-point probe. And the CdS thin films are fabricated by the separate-melting CBD methods through various combinations of time interval from 40 and 60 minutes and temperature range from 70,75,80 and 85°C. It is found that the combination of 85°C and 60 minutes is optimal to obtain smoother surface and more uniform thickness of CdS thin film. Additionally from optical characteristic analysis, in situation of emitted light wave length 500 nm, the transmittance of the cadmium sulphide thin film is 61%. Meanwhile, the band gap is close to theoretical value of 2.4 eV.