Physical structuring is one of the smart ways to explore the maximum capability of a known material, in particular of organic semiconducting materials. Especially, physical structuring at sub-micron and nanoscale dimensions fosters hybrid applications such as in organic photovoltaics, organic light emitting diodes and nonlinear optics as well as in sensors, superhydrophobic and anti-static surfaces.
Various techniques like lithography are designed and employed to create the hierarchical structures. They are sophisticated, energy-intensive processes that require a number of fabricating steps. Interest in simple and inexpensive processing techniques has led to the electrospraying technique which is utilized for generation of microspheres, hollow spheres, porous structures, core-Shell morphology, and other hierarchical structures.
In a recent paper published in Journal of Materials Science, researchers from the Indian Institute of Science at Bengaluru studied the change in physical structures with respect to the addition of moieties or spacers in the chemical structure, with carbazole derivatives as a case study. Therefore, an attempt to understand the effect of spacers, which generally possess a larger degree of rotational freedom on the morphological properties, has also affected other properties. Here, the molecular architecture presents a physical structure-property relationship.
The addition of bithiophene moiety to the carbazole-benzothiadiazole structure at the molecular level led to the change from two-dimensional (2-D) to three dimensional (3-D) pyramids. The authors have also observed that the 2-D and 3-D pyramid structures could be tuned further. Higher concentration provides densely covered structures, higher boiling point solvent provides discrete hierarchical structures, and higher applied voltage provides more periodic structures.
The effect of physical structuring aided in light scattering and multiple absorptions, hence improvement in light absorption up to 44.4% (2-D) and 18.7% (3-D) compared to non-electrosprayed was observed. The ability to regulate the physical structures and enhance percent absorption motivated the team to investigate these structures in organic photovoltaics, wherein various types of bulk heterojunction solar cells were fabricated. Thus, illustrating that by architecture one can give a more tortuous pathway for light, hence increasing the interaction with the targeted material.
Subsequently, these electrosprayed physical structures create a lot of voids and increase the surface area, this aspect assisted in facilitating these structures as superhydrophobic structures. Finally, the effect of depositing these structures on various substrates such as glass, paper, and silicon wafer was demonstrated. Thus, this work endeavors effect of derivatization on morphology, ensuing advancements in optical absorption and superhydrophobicity.
This work is led by Prof. Praveen C. Ramamurthy and his research associate Dr. Khadija K. Khanum at Indian Institute of Science at Bengaluru. The study, Effect of Molecular Architecture on morphology in the Nanostructures and its Applications in Superhydrophobicity and Organic Photovoltaics was recently published in the Journal of Materials Science.