(538f) Surface-Directed Multi-Scale Assembly of Conjugated Polymers

Organic electronic and photoelectronic materials that are light-weight, flexible and can be manufactured using energy-efficient and high-throughput methods. The solution printability at near ambient conditions enables deposition on flexible polymer substrates to create wearable, stretchable, imperceptible electronic devices for use in applications unimagined before. On the other hand, key challenges remain: how does molecular assembly proceed during solution printing and how to control the resulting thin film morphology? The significance of this challenge lies in the fact that charge transport in printed thin films is highly sensitive to their morphological parameters from molecular, mesoscopic to device scale. Addressing this challenge can open up new avenues for attaining high electronic performances, facilitating the much needed structure-property relationship studies in polymer-based electronic devices.

In this talk, I will present a new strategy we recently developed for controlling multi-scale assembly of conjugated polymers that are directly compatible with solution printing. Central to our method is the design of surfaces for overcoming the barrier to polymer nucleation, thereby directing the nucleation-triggered multiscale assembly process during printing. Using this method, we achieved high degree of global and local alignment over large area. In certain cases, we even observed small-molecule-like morphology for high molecular weight conjugated polymers, which has been rarely observed before. With high degree of control over thin film alignment and molecular packing, we correlate these morphological characteristics with anisotropic charge transport properties towards establishing structure-property relationships. By systematically tuning the degree of alignment, we show that the charge transport anisotropy can be switched to favor either transport along the polymer backbone, or along the pi-pi stacking direction.