title: Room temperature solid-state synthesis of a conductive polymer for applications in stable I₂-free dye-sensitized solar cells.
abstract: A solid-state polymerizable monomer, 2,5-dibromo-3,4-propylenedioxythiophene (DBProDOT), was synthesized at 25 °C to produce a conducting polymer, poly(3,4-propylenedioxythiophene) (PProDOT). Crystallographic studies revealed a short interplane distance between DBProDOT molecules, which was responsible for polymerization at low temperature with a lower activation energy and higher exothermic reaction than 2,5-dibromo-3,4-ethylenedioxythiophene (DBEDOT) or its derivatives. Upon solid-state polymerization (SSP) of DBProDOT at 25 °C, PProDOT was obtained in a self-doped state with tribromide ions and an electrical conductivity of 0.05 S cm⁻¹, which is considerably higher than that of chemically-polymerized PProDOT (2×10⁻⁶ S cm⁻¹). Solid-state ¹³C NMR spectroscopy and DFT calculations revealed polarons in PProDOT and a strong perturbation of carbon nuclei in thiophenes as a result of paramagnetic broadening. DBProDOT molecules deeply penetrated and polymerized to fill nanocrystalline TiO₂ pores with PProDOT, which functioned as a hole-transporting material (HTM) for I₂-free solid-state dye-sensitized solar cells (ssDSSCs). With the introduction of an organized mesoporous TiO₂ (OM-TiO₂) layer, the energy conversion efficiency reached 3.5 % at 100 mW cm⁻², which was quite stable up to at least 1500 h. The cell performance and stability was attributed to the high stability of PProDOT, with the high conductivity and improved interfacial contact of the electrode/HTM resulting in reduced interfacial resistance and enhanced electron lifetime.
authors.affiliation: Active Polymer Center for Pattern Integration, Department of Chemical and Biomolecular Engineering, Yonsei University, 50 Yonsei-ro, Seodaemun-gu, Seoul 120-749, South Korea.
authors.forename: Byeonggwan
authors.initials: B
authors.lastname: Kim
authors.forename: Jong Kwan
authors.initials: JK
authors.lastname: Koh
authors.forename: Jeonghun
authors.initials: J
authors.lastname: Kim
authors.forename: Won Seok
authors.initials: WS
authors.lastname: Chi
authors.forename: Jong Hak
authors.initials: JH
authors.lastname: Kim
authors.forename: Eunkyoung
authors.initials: E
authors.lastname: Kim
mesh_terms: D060326:Chemistry Techniques, Synthetic; D004396:Coloring Agents / Q000737:chemistry*; D004553:Electric Conductivity; D011211:Electric Power Supplies; D008958:Models, Molecular; D008968:Molecular Conformation; D058608:Nanopores; D058105:Polymerization; D011108:Polymers / Q000138:chemical synthesis* / Q000737:chemistry*; D012993:Solar Energy; D013696:Temperature; D014025:Titanium / Q000737:chemistry
chemical_list: D004396:Coloring Agents; D011108:Polymers; C009495:titanium dioxide; D014025:Titanium