Bio-Inspired Controllable Liquid Transfer: From Fundamentals in Micro-Patterning to Applications in Optoelectronics.

Solution-processed micro-patterning is a crucial process for making high-performance optoelectronic devices, since the carrier transfer behavior is closely related to the uniformity, orientation, and resolution of micro-patterns. Developing solution processes with good controllability has thus attracted increasing research interest in the last decade. Inspired by Chinese brushes, a fibrous-guided direct-writing strategy is recently developed that enables controllable liquid transfer for making micro-patterns, which is systematically reviewed from viewpoints of both the fundamentals in liquid manipulation and the applications in optoelectronics. First, a model structure of dual-conical fibers (CFs) is proposed, whose capacity in liquid transfer is featured as the dynamic liquid balance and the uniform liquid film. On the basis, triple- and multi- CFs are developed for transferring liquid onto the target substrate in a controllable manner, where the tri-phase contact line can be finely tuned. Thereafter, micro-patterns with µm-scale resolution, cm-scale uniformity, and molecular-scale orientation can be achieved, as is demonstrated by the as-prepared ultrasmooth quantum dot films, highly aligned silver nanowires films, and wrinkle-free reduced graphene oxide films, respectively. The high-performance optoelectronic devices, including quantum dot light-emitting diodes, flexible transparent electrodes, and pressure sensors, are demonstrated. Perspectives for solution-processed micro-patterning in optoelectronics are also suggested.