High‐temperature annealing is essential to crystallize sol–gel spin‐coated ZnO films but is a critical disadvantage in manufacturing flexible and transparent electronics, owing to low thermal stability of polymer substrates. Thus, a novel annealing method, named thermal dissipation annealing (TDA), is developed. TDA method can anneal ZnO films without any deformation of polymer substrates. The effects of TDA method are confirmed by annealing ZnO films deposited on glass and polyethylene naphthalate substrates. Moreover, In‐doped ZnO (IZO) films are annealed by TDA method, and the properties of IZO films are investigated. ZnO films annealed by TDA method show graphene‐like nanosheets and exhibit much higher photosensitivity than ZnO films annealed by furnace or infrared (IR) lamp. For IZO films annealed by TDA method, entangled nanosheets begin to unravel with increasing doping concentration, and size of nanosheets significantly decreases at 0.04 at%. The photosensitivity of the IZO films decreases from 21.77 to 2.76 with increasing doping concentration. Therefore, flexible and transparent UV photodetectors based on sol–gel spin‐coated ZnO films can be fabricated through TDA method; however, when ZnO films annealed by TDA method are utilized to UV photodetectors, In dopant is not a suitable material to improve the performance of UV photodetectors.

Because of their simplicity and low equipment costs, various oxidation methods can be used to create metal oxides, but they still require long processing times and/or high temperatures. In this study, a new electrochemical oxidation (ECO) method, which oxidizes metal in DI water with a constant flowing current to both the cathode and anode, was developed to overcome the disadvantages of conventional oxidation methods. The mechanism of the ECO method is discussed. Metallic Zn films were oxidized by the ECO method in DI water for 1 h. The DI water temperature was varied from 30 to 90 ^oC to determine the optimal temperature for the ECO process. Increasing the temperature of the DI water led to distinct surface changes in the disk-shaped Zn plate. The intensity of diffraction peaks from the ZnO (002) plane gradually increased from 31.67 to 2806.48. The structural and optical properties of the ZnO thin film were enhanced as the temperature of the DI water approached 90 ^oC, which means that a high-quality ZnO thin film was synthesized using the ECO method at lower temperatures and shorter processing time compared with established oxidation methods. These results confirm the ECO method can be useful for the low-cost fabrication of transparent and flexible optoelectronic devices.

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