Heat-light soaking effects on Cu(In,Ga)Se-2 (CIGS) solar cells with atomic layer deposition (ALD)-Zn(O,S) and chemical bath deposition (CBD)-ZnS(O,OH) buffer layers were investigated using temperature-dependent current-voltage and admittance spectroscopy measurements. Both CBD-ZnS(O,OH)/CIGS and ALD-Zn(O,S)/CIGS solar cells showed a significant increase in the cell performance after the combined heat and light soaking (HLS) post-treatment. Temperature-dependent current-voltage measurements showed a reduced roll-over of current density-voltage curve after the HLS post-treatment, suggesting a reduced recombination at the absorber/buffer interface. Admittance spectroscopy measurement revealed a remarkable shift towards shallower energy positions for the defect NI after HLS post-treatment in both CIGS solar cells fabricated using CBD and ALD methods. By optimizing the HLS and the deposition conditions for each buffer layer, CBD-ZnS(O,OH)/CIGS and ALD-Zn(O,S)/CIGS solar cells yielded total efficiencies of 18.8 and 18.7%, respectively. (c) 2015 Elsevier B.V. All rights reserved.