CIGS formation by high temperature selenization of metal precursors in H2Se atmosphere

Cu(In1−xGax)Se2 (CIGS) thin film have been fabricated by a 2-step process using Cu–In–Ga precursors and H2Se gas. A high temperature selenization and in situ annealing process was developed to improve the optoelectronic quality and increase the band gap at the surface of the CIGS absorber. Characterization with SEM and XRD showed the films had large grain size and improved crystallinity. SIMS and PL analysis showed the Ga content at the surface of the absorber was increased and the band gap was higher. Completed solar cells showed Voc increase resulted from more than one order of magnitude decrease in the saturation current compared to cells selenized at lower temperature. A high Voc of 623 mV was achieved and the best cell had conversion efficiency exceeding 15%.

► We developed high temperature selenization of Cu–In–Ga precursor in H2Se with in situ anneal.
► We showed improved grain size and crystallinity of the CIGS absorber.
► We showed higher band gap and increase in Ga concentration at the surface of the absorber.
► We demonstrated Voc great than 600 mV.