RELATION BETWEEN ELECTROLUMINESCENCE AND ELECTRON-TRANSPORT CHARACTERISTICS OF SUBSTITUTED POLY(PHENYLENEVINYLENE)S

The influence of conditions of electrode coating with a polymer film a nd features of carrier transport through the polymer layer on the char acteristics of photo- and electroluminescence was considered for poly( 1,4-phenylene-1-phenylvinylene) (MP-PPV), oly[1,4-phenylene-1,2-di(4-m ethoxyphenyl)vinylene] (DMOP-PPV), and oly[1,4-phenylene-1,2-di(4-phen oxyphenyl)vinylene] (DPOP-PPV). It was found that electroluminescence efficiency increases by more than two orders of magnitude in going fro m MP-PPV and DMOP-PPV to DPOP-PPV. This difference is associated with the fact that mobile charge carriers in DPOP-PPV are of both signs and radiative charge recombination occurs in the bulk of the polymer. In the case of MP-PPV or DMOP-PPV, this process occurs at the cathode, wh ere electrons injected into the polymer are localized and the radiativ e recombination competes with the direct discharge of the holes at the cathode. It was shown that the quantum efficiency of electroluminesce nce is an order of magnitude higher for vacuum-deposited polymer layer s than for films spin-cast from solution.