The influence of cracked selenium flux on CIGS thin film growth and device performance prepared by two-step selenization processes

Thermal-cracking system has been adopted to produce cracked selenium and the influence of cracked selenium flux on the structure and reaction pathway during the first-step selenization is investigated. High Cracked-Selenium (HC-Se) may facilitate the Cu-Se and In-Se reaction at lower temperatures. The Polygon grains observed in the HC-Se samples play a key role in further selenium diffusion into the film since they make the film more incompact In addition, activation energy analysis indicates that Cu2-xSe and beta-In2Se3 formed in the samples prepared in HC-Se atmosphere may result in different growth pathway of Cu(In1-xGax)Se-2 (CIGS) thin film compared with that prepared in Low Cracked-Selenium (LC-Se) atmosphere during the first-step selenization, which restrains lamination in CIGS films effectively so that the distribution of Ga is more uniform throughout CIGS films and no small grains of CuGaSe2 (CGS) accumulate near the Mo back-contact. As a result, the shunt conductance in this CIGS thin film device prepared in HC-Se is reduced, and the fill factor, open-circuit voltage, as well as the cell efficiency are improved. (C) 2015 Elsevier B.V. All rights reserved.