Importance of internal stress control in organic/metal-oxide hybrid devices

Incorporation of functional metal oxides in organic devices enables the creation of electronic devices that have both the advantages of organic materials, such as flexibility and light weight, as well as those of metal oxide materials, such as optical transparency and stability against ambient air. However, developing high-performance organic/metal-oxide hybrid devices is challenging, because the deposition of a metal oxide onto an organic semiconductor layer severely damages the device for reasons that are not well understood. In this study, we clarified that the internal stress of the metal oxide is the cause of this damage. A hybrid device composed of an organic semiconductor layer sandwiched between two indium tin oxide electrodes was investigated as a typical organic/metal-oxide hybrid device. The internal stress in the metal oxide layer causes the formation of nanometer-order clearances at the weak bonding interface in the device; this damage reduces the electrical conductivity of the device by over two orders of magnitude. A method to control the internal stress of the metal oxide layer by introducing a gas that affects crystal growth during metal oxide deposition was developed, and an undamaged hybrid device was demonstrated by controlling the internal stress of the metal oxide. High-performance organic/metal-oxide hybrid devices without the damage may be key devices that open up electronics with features beyond those possible with the organic electronics and metal oxide electronics.