NF thin films have been prepared via chemical bath deposition (CBD)
as described in our earlier reports.34 (link),45 (link) ZTO and CIGS/InS
layers have been deposited on the ZnO nanostructured thin films via
ultrasonic spray pyrolysis.46 (link)−49 (link) For the ZTO layer, 25 mM zinc acetate dihydrate (Zn(CH3COO)2·2H2O, Sigma-Aldrich, 99%)
and 75 mM tin(IV) chloride pentahydrate (SnCl4·5H2O, Sigma-Aldrich, 98%) were dissolved in methanol–deionized
water (v/v = 3:1) and sprayed on the ZnO thin films with a 20 pass
number, 48 kHz at 200 °C. The ZTO layer was then annealed at
550 °C for 2 h for complete transformation of the ZnSn(OH)6 phase to ZTO. CIGS and In2S3 layers
were deposited as described in the literature.44 (link) The thin-film electrode preparation route is schematically
summarized in