Poly(alkylthio-p-phenylenevinylene): Synthesis and electroluminescent and photovoltaic properties

Two alkylthio-substituted poly(p-phenylenevinylene) (AT-PPV) derivatives, poly(2-octylthio-p-phenylenevinylene) (OT-PPV) and poly[5-methoxy-2-(2′- ethyl-hexylthio)-p-phenylenevinylene] (MEHT-PPV), were synthesized by a Heck coupling reaction for the investigation of the effect of alkylthio groups on the optoelectronic properties of poly(p-phenylenevinylene) derivatives. The absorption peaks of OT-PPV and MEHT-PPV solutions were located at 431 and 438 nm, respectively. As for solid films, an OT-PPV film showed an absorption maximum wavelength at 444 nm, 13 nm redshifted in comparison with its solution value, whereas an MEHT-PPV film displayed the same absorption peak position as its dilute solution; this indicated that there was no interchain interaction in the MEHT-PPV film. Polymeric light-emitting diodes (PLEDs) and polymer solar cells (PSCs) based on OT-PPV and MEHT-PPV were fabricated and characterized. Very narrow bandwidths of the electroluminescence (EL) spectra of the two AT-PPVs were found, with the full width at half-maximum of the emission being 40 and 47 nm for OT-PPV and MEHT-PPV, respectively. The maximum EL efficiency of the single-layer PLED based on MEHT-PPV with Al as a cathode reached 1.49 cd/A. The PSC based on a blend of OT-PPV and [6,6]-phenyl-C₆₁ butyric acid methyl ester (PCBM) showed the power conversion efficiency of 1.4% under the illumination of AM1.5 (80 mW/cm²).