Surface morphology control of In2S3 buffer layer by Sn incorporation and its application to cadmium free Cu(In,Ga)Se2 thin film solar cells
Abstract Sn atoms were incorporated into In 2 S 3 thin film to modify the morphology of the In 2 S 3 buffer layer for Cd free Cu(In,Ga)Se 2 (CIGS) thin film solar cells. The incorporation of Sn atoms into the In 2 S 3 films was carried out by adding a SnCl 2 dissolved solution to an InCl 3 and CH 3 CSNH 2 dissolved solution during chemical bath deposition process. With Sn incorporation into In 2 S 3 film, the surface morphology of In 2 S 3 film was significantly changed showing more uniform and smooth film. Raman spectroscopic analysis shows that the backbone of In 2 S 3 lattice disappear completely with 10% Sn incorporation in the film. In addition to effect of Sn content on the surface morphology of In 2 S 3 film, we found that the morphology of Sn incorporated In 2 S 3 film strongly depends on the pH value in the reaction solution. At the pH value of 2.53, the film became very dense without pores and secondary phases. The film was completely covered the surface of CIGS substrate. Photoluminescence analysis indicates that the shallow acceptor levels at the CIGS surface might be passivated by Sn doping during chemical bath deposition process. As a result, the efficiency of CIGS solar cell with 4.9% Sn doped In 2 S 3 buffer was improved from 9.98 to 12.7%