Drop-Dry Deposition of SnO₂ Using a Complexing Agent and Fabrication of Heterojunctions with Co₃O₄

The drop-dry deposition (DDD) is a simple chemical technique of thin film deposition, which can be applied to metal oxides. The deposition solution is an aqueous solution including a metal salt and an alkali. However, some metal ions react spontaneously with water and precipitate. This work is the first attempt to use complexing agents in DDD to suppress the precipitation. SnO₂ thin films are fabricated using DDD with Na₂S₂O₃ as a complexing agent and via annealing in air. The results of the Auger electron spectroscopy measurement show that the O/Sn composition ratio of the annealed films approached two, indicating that the annealed films are SnO₂. The photoelectrochemical measurement results show that the annealed films are n-type. Co₃O₄/SnO₂ heterojunction is fabricated using p-type Co₃O₄ films which are also deposited via DDD. The heterojunction has rectification and photovoltaic properties. Thus, for the first time, a metal oxide thin film was successfully prepared via DDD using a complexing agent, and oxide thin film solar cells are successfully prepared using only DDD.