Expanding\nthe Notch\nRegion by Adjusting the Copper\nGrowth Profile for High-Efficiency Flexible Cu(In,Ga)Se<sub>2</sub> Solar Cells

Flexible CIGS solar cells, with their\nadjustable band\ngap for future\nflexible tandem solar cells and flexibility for roll-to-roll manufacturing,\nhave the potential to be used in a wide range of applications. However,\nflexible CIGS solar cells are always manufactured at relatively low\ntemperatures, where Cu diffusion has a substantial impact on the CIGS\nsurface state and defect formation. To address these issues, we designed\na new CIGS growth profile in this work by carefully examining the\neffects of different locations of excess Cu in the third stage of\nthe CIGS deposition profile. The results showed that adding more Cu\nto the middle part of the third stage can enhance the crystal quality,\nexpand the GGI grading notch region, move the GGI minimum to the CdS\nside, cause a <i>J</i><sub>SC</sub> rise, achieve proper\nband alignment at the interface, and then enhance the FF. By taking\nadvantage of these advantages, the photoelectric conversion efficiency\n(PCE) is significantly raised. An impressive improvement of 32.6%\nover the initial efficiency of 13.8% has been attained, yielding a\nhigh efficiency of 18.3% and providing a strong basis for the development\nof flexible CIGS solar cells.