“…Zinc oxide (ZnO) is one of the most widely researched semiconductor oxides, owing to its many versatile and attractive properties, such as high chemical and thermal stability, non-toxicity [1], ease of preparation, tunable direct wide band gap (3.4 eV), and high transparency in the visible region [2]. These properties saw ZnO thin films fabricated for various industrial applications, e.g., in optoelectronic devices [3], lasers, gas sensors, and ultraviolet (UV) light emitters [4], and as protective surface coatings [5]. ZnO plays important roles in a number of solar cell systems, such as silicon-based solar cells (first-generation), thin films (second generation), and organic multi-junction, dye-sensitized (third-generation) systems, either as a transparent conductive oxide (TCO) or as a junction for exciton separation [6].…”