Bifacial CIGS (11% efficiency)/Si solar cells by Cd-free and sodium-free green process integrated with CIGS TFTs

CuInGaSe₂ (CIGS) thin-film has successfully grown at low temperature 400°C for bifacial solar cells and TFTs without degrading the silicon solar cell on the other side. The efficiency of CIGS solar cells reached 6.3% and 11% at 400 and 500°C, respectively, by sodium-free and Cd-free (n-type ZnS buffer layer used) green technologies. Texturing technique has been introduced here on Si not only to relieve the sodium-free impact on CIGS-crystallization but also to enhance the adhesion between CIGS solar cells and underneath substrate. CIGS TFTs are reported first time and revealed a record-high hole-mobility of 0.22 cm²/V-s. Hybrid CIGS solar cells/TFTs are uniformly formed on 6" wafers, simultaneously powered with silicon solar cells.