“…A thin layer of zinc oxide (ZnO) was prepared by a sol-gel method [38,39]. A 2-methoxyethanol (0.97 mL, Wako, Osaka, Japan) solution containing zinc acetate dihydrate (0.1098 g/mL, Wako, 99%) and monoethanolamine (0.03 mL, Nacalai Tesque, Kyoto, Japan) was spin-coated at 2000 rpm on a pre-cleaned indium-doped tin oxide (ITO, Xin Yan Technology, Kowloon, Hong Kong, ~10 Ω/□) glass substrate.…”