Femtosecond Laser Scribing of Cu(In,Ga)Se2 Thin-Film Solar Cell

We have made a comparative review of photovoltaic properties of laboratory-scale Cu(In,Ga)Se-2 (CIGS) solar cells electrically-isolated from each other by two types of femtosecond laser scribes: "Type 1" with removing both transparent conductive oxide (TCO) and CIGS layers and "Type 2" with complete removal of only TCO. The shunt resistance drastically decreased in the case of the "Type 1" scribing, degrading the photovoltaic efficiency. The "Type 2" scribing did not accompany a sharp drop in the shunt resistance, keeping relatively-high efficiency. The difference in the efficiency between before and after the "Type 2" scribing was only 0.1, while a typical drop for the "Type 1" was 1.3. In order to investigate the laser irradiation effect on a buried p-n junction in the "Type 2" laser-scribed CIGS solar cells, an electron-beam-induced current (EBIC) analysis was also performed. As a result, EBIC signals were clearly observed along a sidewall of the laser-scribed trench, indicating that the p-n junction survived after our femtosecond laser scribing even at the sidewall of the laser-scribed trench. Femtosecond laser scribing is an effective tool for CIGS solar cells with keeping high efficiency.