Selective Ablation in Cu(In,Ga)Se2 thin-film solar cells – analysis of different process regimes at sub-picosecond to nanosecond pulse duration.

Abstract

Recent achievements in Cu(In,Ga)Se2 (CIGS) thin film technology allow the industrial production ofhighly efficient solar modules. A large growth of the CIGS-based solar cell production volume can beexpected for the coming years thanks to some favorable properties inherent to this absorber type. A majordrawback of CIGS is the inefficient patterning process. Since CIGS is a particularly difficult material forlaser ablation there is still no industrial all-laser scribing solution available. Manufacturers fall back onmechanical needle scribing for the P2 and P3 scribing process and have to accept substantial broadeningof the electrical interconnects due to unpredictable chipping at the scribe borders. In the present study weexplored a large variety of possible processes for the P1-P3 scribing at different wavelengths and indifferent pulse duration regimes. Beside the direct ablation of CIGS with ultrashort pulses we alsoinvestigated more exotic processes like layer side lift-off variants. The resulting scribes were analyzedusing electron microscopy (EM), laser scanning microscopy (LSM), energy dispersive X-ray spectroscopy(EDX) and electrical conductivity measurements. The most promising processes were selected forproducing functional mini-modules. Multiple optimization cycles allowed us to select the processes withthe best performance in the mini-module.