Inkjet printing is a material-conserving deposition technique used for liquid phase materials. By virtue of convenience, low-cost, flexibility and speediness, inkjet printing has become one of the most promising candidates for fabricating high-quality patterns. In recent years, inkjet printing has aroused wide attention in functional device research area. The “coffee ring” effect is a common phenomenon in inkjet printing. It directly influences the depositional morphology, which affects the resolution of patterns and the performance of devices. It is very important to research the “coffee ring” effect in inkjet printing. In this paper, we present the recent research progress of the “coffee ring” effect in the process of droplet evaporation. Firstly, the forming mechanism and suppressing methods of “coffee ring” effect are discussed. Secondly, the applications by suppressing or utilizing the “coffee ring” effect in inkjet printing, such as high quality photonic crystal pattern, high sensitive sensor, semiconductor film, transparent conducting film and short-channel transistor are introduced. Finally, a perspective on the remaining challenges of controlling “coffee ring” effect in inkjet printing is proposed. The broad research and application of combining the controlling “coffee ring” effect in inkjet printing and nano-material preparation are discussed. It will be of great significance for patterning, functional device research and 3D printing technology.

Contents
1 Introduction
2 “Coffee ring” effect
2.1 Forming mechanism of “Coffee ring” effect
2.2 Suppressing methods of “Coffee ring” effect
3 Suppressing or utilizing “coffee ring” effect in inkjet printing
3.1 Suppressing “coffee ring” effect in inkjet printing
3.2 Utilizing “coffee ring” effect in inkjet printing
4 Conclusion and outlook