Abstract
A molybdenum trioxide thin film with smooth surface and uniform thickness was successfully achieved by an electrospray deposition method using an aqueous solution with a drastically low concentration of 0.05 wt%. Previous papers demonstrated that an additive solvent technique is useful for depositing the thin film by the electrospray deposition, and the high vapor pressure and a low surface tension of an additive solvent were found to be important factors. As a result, the smooth molybdenum trioxide thin film was obtained when the acetonitrile was used as the additive solvent. Furthermore, the vapor pressure of acetone is much higher than that of aqueous solution, and this indicates that the acetone is easily evaporated after spraying from the glass capillary. By optimizing a concentration of acetone in the molybdenum aqueous solution, a minimum root mean square roughness of the MoO3 thin film became 3.7 nm. In addition, an organic photovoltaic cell was also demonstrated using the molybdenum trioxide as a hole transport layer. Highest photoconversion efficiency was 1.72%, a value comparable to that using conventional thermal evaporation process even though the aqueous solution was used for the solution process. The photovonversion efficiency was not an optimized value, and the higher value can be achieved by optimizing the coating condition of the active layer.
Highlights
Organic thin films can be formed by several solution processes such as conventional spin-coating, inkjet printing, gravure printing, screen printing, doctor blading, and ultrasonic spraying methods [1,2]
Several kinds of organic thin film devices, including organic light-emitting diodes (OLEDs) [3], organic photovoltaic cells (OPVs) [4,5,6], organic image sensors [7], and organic thin-film transistors [8,9] have been investigated for future printed/ambient electronics applications. This is because specific organic molecules exhibit high photoluminescence quantum efficiency [10], high optical-to-electrical conversion efficiency, selective absorption band in the visible wavelength region [11], and high carrier mobility compared to conventional inorganic materials [12]
The MoO3 was difficult to be formed by the conventional solution process, and we investigated the optimized fabrication process for the MoO3 thin film by the electrospray deposition (ESD) process using an aqueous solution
Summary
Organic thin films can be formed by several solution processes such as conventional spin-coating, inkjet printing, gravure printing, screen printing, doctor blading, and ultrasonic spraying methods [1,2]. Several kinds of organic thin film devices, including organic light-emitting diodes (OLEDs) [3], organic photovoltaic cells (OPVs) [4,5,6], organic image sensors [7], and organic thin-film transistors [8,9] have been investigated for future printed/ambient electronics applications. This is because specific organic molecules exhibit high photoluminescence quantum efficiency [10], high optical-to-electrical conversion efficiency, selective absorption band in the visible wavelength region [11], and high carrier mobility compared to conventional inorganic materials [12]. An efficient electrospray was not realized owing to the low dielectric constant of normal solutions containing organic semiconductors
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