합성을 통한 고분자 3차원 특성 향상에 관한 연구

Abstract

In conjugated polymer, the role of intermolecular interaction is ubiquitous. Most of properties of conducting polymer are governed by solid state morphology. These morphologies could significantly have influenced on intermolecular interactions which are above mentioned. Among several properties of conducting polymer, charge transport ability is one of the important issues for utilizing in optoelectronic devices like organic photovoltaic (OPV), Organic field-effect transistor (OFET), and organic light-emitting diode (OLED), etc. Efficient carrier mobility in conjugated polymer is determined by intramolecular and intermolecular charge transport . To accomplish efficient intermolecular overlap with neighboring molecules, control of intermolecular interaction between polymers and resulting morphology is critical to improving charge transport. Desirable morphology for several optoelectronic devices are almost different. In OTFT, polymer film should have edge-on dominant crystal packing with locally aggregated state. In OPV, desirable morphology is quite complicated than OTFT, interconnected phase separation, proper aggregation, and isotropic or face-on crystal orientation and another requirement should be fulfilled. For this purpose, control of intermolecular interaction could be important key. Thus, in my research, I controlled intermolecular interaction through several approaches in order to improve device performance. In chapter 2, I tried to control 3-D morphology in OPV BHJ system by adding composition gradient inducer. The delicately designed gradient inducers (F-ADD and Br-ADD) have selective interaction to PCBM and PTB7, respectively. These could control the surface energy of each component’s aggregates. The BHJs with a vertically homogenous compositional distribution and small domain sizes formed under optimized condition which have similar surface energy between donor and PCBM. These BHJ devices exhibited better photovoltaic performances than the nanostructured BHJ devices with vertical gradients. These enhancements in OPV devices is attributed to improve charge collection and separation efficiency which is generally governed by morphology and interface between Donor and PCBM. In chapter 3, I focused on enhancing interconnectivity by introducing strong - interaction inducer. Modifying the structures of conducting polymer by incorporating - interaction inducer could enhance the intermolecular interactions resulting in enhanced interconnectivity and charge transport ability. First, I investigated the interconnected structure of incorporating 3,6-carbazole units into conjugated polymers based on 2,7-carbazole. Development of thermally stable polymer:fullerene blends with optimized PCEs is an important goal in this area of research. I studied the morphologies of the copolymers incorporating 3,6-carbazole units resulting from thermal annealing to investigate the effects of the difference between the Tg values of the 2,7-carbazole unit (127 °C) and the 3,6-carbazole unit (161 °C). Second, the molecular weight reduction effect due to the introduction of 3,6-carbazole was minimized, and the charge transfer according to the amount of introduction was systematically analyzed. This copolymer series permitted us to study the effects of the incorporated 3,6-carbazole units on the intermolecular interactions, which can affect non-geminated recombination in BHJ-PSCs. Third, I extended this concept to other copolymer which iscomposed with benzo[1,2-b:4,5:b’]dithiophene (BDT) and 2,1,3-benzothiadiazole (BT). The random copolymer formed by combining these polymers was expected to have high hole mobility and a favorable HOMO energy level. Finally, the random polymer was applied to hole transport material in perovskite solar cell. In this chapter 4, I have mainly studied the control of the three-dimensional structure of the polymer by controlling the side chain. The morphology control through side chain tailoring has been very helpful in deepen studying charge transfer dynamics. First, I control the intermolecular interactions by controlling the bulkiness of the side chain of the polymer chain. To investigate the side chain bulkiness effect on polymeric morphology and packing structure, I systematically introduced different bulk alkyl chains such as 2-ethylhexyl, 2-butyloctyl and 2-octydodecyl. Although polymer with the bulkiest side chains formed the larger fibrillar structures, it could not form efficient 3-D charge transport pathways due to the lack of well-ordered edge-on lamellar packing. These results imply the significance of forming the efficient charge transport pathways as well as the beneficial film morphologies for charge-carrier transport in devices. And then, For systemic study of effects of crystallinity and crystal orientation on charge transport ability, delicately controlled P5-2 was synthesized and it can be easily controlled crystal orientation and crystallinity. In melt-crystallization, the crystal will be reoriented to edge-on orientation due to the absence solvent and highly planar backbone structure. Second, I noticed the orientation of the polymer crystals. For systemic study of effects of crystallinity and crystal orientation on charge transport ability, delicately controlled P5-2 was synthesized and it can be easily controlled crystal orientation and crystallinity. In melt-crystallization, the crystal will be reoriented to edge-on orientation due to the absence solvent and highly planar backbone structure. Finally, I applied above strategy to the organic solar cell field. I and my coworker have designed and synthesized a series of 2D-BDT-based active materials with various numbers of BDT units. With an increase in the number of 2D-BDT units, we could manipulate intermolecular interactions, thus producing the desired interconnectivity in the BHJ.