Reaction paths during the sulfurization of In Cu Ga and Cu In Ga thin films for the fabrication of Cu In,Ga S2 at different heating rates

The purpose of this work is to investigate the reaction paths during the sulfurization of two types of metallic precursors, In Cu Ga bilayers and Cu In Ga single layers. The metallic precursors were sulfurized in a closed volume at three constant heating rates 14 Kmin 1, 28 Kmin 1 and 56 Kmin 1. We use synchrotron based polychromatic X ray diffraction to monitor in real time the formation of the Cu In,Ga S2 thin films. The sequence of solid phases before the formation of the chalcopyrite phase, and the temperatures of the phase transitions depend on the heating rate and on the metallic precursor. As for the In Cu Ga bilayers, we found that increasing the heating rates shifts the onset of the sulfurization to higher temperatures. Decreasing the heating rate favors the formation of CuS and Cu Ga intermetallic phases. As for the Cu In Ga single layers, we found a significant composition caused strain of the Cux In,Ga y phases during the sulfurization. Furthermore, the Cu In,Ga S2 thin films fabricated from these single layered precursors presented a bad adhesion to the Mo back contact. We developed a one step rapid thermal process RTP where suitable Cu In,Ga S2 thin films for solar cells were obtaine