KAIST CBE Special Seminar
- Speaker: Dr. Youngmin Lee
Department of Chemical Engineering, The Pennsylvania State University
- Title: Synthesis and Self-assembly of Fully Conjugated Block Copolymers for Organic Photovoltaics
- Schedule: Thursday, August 27, 2015 / 4 PM
- Place: #1101 @ W1-3 Bldg.
Donor-Acceptor fully conjugated block copolymers have the potential to overcome the limitations of mixtures and blends as photoactive layers in solar cells. Those enable to tune donor/acceptor interfaces and adopt the mesoscale structure within the active layer of organic photovoltaic devices. The ability to control and modify the micro-phase separation of the block copolymer can offer a useful platform in understand the relationship between chemical structure, nanoscale morphology, and photovoltaic device performance. Furthermore, they may serve as model systems to study fundamental questions regarding optoelectric properties and charge transfer. However, the synthesis of fully conjugated block copolymers remains a challenge. In this talk, synthesis of poly(3-hexylthiophene)−block−poly-((9,9-dioctylfluorene)-2,7-diyl-alt-[4,7-bis(thiophen-5-yl)-2,1,3-benzothiadiazole]-2′,2″-diyl) (P3HT-b-PFTBT) will be presented by two-step reactions comprised of Grignard metathesis for polymerization of P3HT followed by chain extension through a Suzuki-Miyaura polycondensation. By optimization of reaction conditions in terms of the concentration of the Grignard reagent and feed ratio of monomers for the Suzuki-Miyaura reaction, the amount of uncoupled homopolymers were effectively minimized. Next, the relationship between self-assembly and photovoltaic performance of P3HT-b-PFTBT will be presented. Orientation and crystallization of P3HT-b-PFTBT were controlled by solvent additive and random copolymerization with 3-octyl thiophene. When crystallization suppressed, microphase separation of the block copolymer promoted, which led to enhanced photovoltaic performance. The relationship between the synthesis, self-assembly and electrical characteristics of the P3HT-b-PFTBT was demonstrated and these strategies can be utilized for new donor-acceptor fully conjugated block copolymers beyond P3HT-b-PFTBT.