The influence of pre-heating temperature on the CIGS thin film growth and device performance prepared in cracked-Se atmosphere
The influence of pre-heating temperature on cracked–selenized Cu(In, Ga)Se2 (CIGS) films' structure, growth kinetics, and photovoltaic performance is investigated. The 'large island grains' on the upper surface are the precursors of Cu2−xSe and finally evolve into Cu2−xSe as the pre-heating temperature increases to 400 °C. The 'large island grains', as well as In2Se3, are considered to be two decisive factors in forming CIGS as they facilitate the diffusion of cracked-Se into the thin films, because they make the films more incompact and suppress the fast formation of complete single CuInSe2 (CIS) during the 2nd heating. Stoichiometric CIGS thin films without a bi-layer structure and phase separation can be achieved by adjusting the appropriate pre-heating temperature. The performance of the solar cells is mainly influenced by the current leakage caused by small grains and cavities near the CIGS/Mo back contact.