Microanalysis of laser micro-welded interconnections in CIGS PV modules

Laser micro-welding is a technique that can be used for interconnective (P2) patterning of Cu(In,Ga)Se2 (CIGS) thin film solar cells after deposition of the ZnO:Al window layer. The micro-welding process transforms CIGS into a conductive compound that forms a contact between the ZnO:Al front contact and the Mo back contact. In this work we present a study on the influence of process parameters on the interconnectivity of the laser micro-weld as well as an investigation of the morphology of the micro-weld zone. We found that the current method results in an overlap of conditions where electrical connection is achieved and where Mo/glass damage is caused by laser action. Stability testing shows that interconnections processed without appreciable damage are stable. The connecting region contained metal rich zones and segregated CuxSe that we believe account for its conductivity. ► Laser processing allows post-ZnO:Al connective P2 scribing in CIGS solar cells. ► Connectivity of these scribe lines depends on the residual phases present. ► Simple Gaussian laser beams damage the layers severely at the beam center. ► Defocusing was necessary to achieve working devices.