Blends of poly[2-( 2 ′ , 5 ′ -bis( 2 ′ -ethyl-hexyloxy)phenyl)-1,4-phenylenevinylene] and poly(3-hexylthiophene) as base materials for broad band light emission devices

Photoluminescence (PL) and electroluminescence (EL) emission from blended films composed by poly[2-( 2 ′ , 5 ′ -bis( 2 ′ -ethyl-hexyloxy)phenyl)-1,4-phenylenevinylene] (BEHP-PPV) and poly(3- hexylthiophene) (P3HT) conjugated polymers with different relative concentrations are investigated. The main changes observed on the PL spectra of the blended films with temperature and excitation power are associated to an increase of the emission efficiency of the P3HT constituent. The EL spectrum of a light emission device (LED) fabricated with the BEHP-PPV:P3HT blend presents a similar broad emission as in the PL measurement but shifted to higher wavelengths. The blended LEDs show a significantly higher emission efficiency than the LEDs made with the pure constituents. The apparent color of the blended LED shifts to a purer red as the applied voltage is increased. This tuning capacity was interpreted as due to a change in the effective gap of the blend caused by the redistribution of injected carriers in the BEHP-PPV:P3HT interfaces under bias. These characteristics make the BEHP-PPV:P3HT blend a very attractive material for fabrication of efficient red LEDs.