Picosecond laser modification of CIGS active layer

Cu-chalcopyrite based solar cells such as Cu(In,Ga)Se₂ (CIGS) have been established as the most efficient thin-film technology in converting sunlight into electricity. Laser scribed monolithic interconnects are one of the key technologies which will play a significant role in future develop-ments of CIGS technology. Laser scribing is needed to maintain module efficiency by dividing large scale device to smaller cells interconnected in series. CIGS layer is a thermally sensitive material, and laser modification can induce local structural changes of the active layer and significantly modi-fy the electrical properties. Therefore, the laser modified region can act as series interconnect be-tween the adjacent cells. In this study, we investigated the laser modification of the CIGS active layer with picosecond laser. The EDS analysis revealed the increase of Cu/(In+Ga) ratio in laser treated areas while Raman measurements indicated changes in main CIGS peak and formation of the Cu-rich CuGaSe₂ phase. Therefore, this resulted in significant electrical conductivity increase in laser-treated areas. Electrical testing of the laser performed P2 micro-welds showed scribe conduc-tivities up to 9.3 Ω·cm which are acceptable for the cell serial interconnection.