| 초록 |
Tin-based alternating copolymers with a uniform π-conjugated segment were synthesized using the Heck reaction between distyrylstannane monomer and various difunctionalized monomers. The UV-visible absorption maximum peaks of the resulting polymers in thin films appeared in the wavelength range of 347 ~ 394 nm. Their photoluminescence spectra exhibited an emissive maximum peak around 470 ~ 502 nm, corresponding to blue light emission. Multi-layered light-emitting diodes with ITO/PEDOT (50nm)/Polymer (80nm)/Ca (50nm)/Al (200nm) composition exhibited an emissive maximum peak in the range of 464 ~ 472 nm. All of the materials exhibited an extremely low turn-on voltage of less than 4 V. From cyclic voltammetric studies and optical data, the LUMO level is estimated to be 3.21 eV for SnPhFPV and 2.93 eV for SnPhPVK, and the ionization potentials (HOMO level) were estimated to be 5.89 eV for SnPhFPV and 5.64 eV for SnPhPVK. This lowered LUMO level reduces the energy barrier to electron injection, resulting in a lowering of the operating voltage in the polymeric LED. Compared to devices based on the tin-based polymers alone, devices based on blends between the tin-based polymers and PVK showed improved efficiency of power and luminescence by at least 2-4 times and 3-6 times, respectively. Also for these polymer:PVK blends, the electroluminescence efficiency enhances up to the range of 0.1 ~ 0.3 lm/W and the purity of the emitted blue color improves. |
