Improving light efficiency of white polymer light emitting diodes by introducing the TPBi exciton protection layer

We fabricated and evaluated the efficient white polymer light emitting diode (WPLED) by introducing TPBi exciton protection layer with ITO/PEDOT:PSS/PFO:MEH-PPV/TPBi/LiF/Al structure. PFO and MEH-PPV were prepared by the spin coating as the light emitting host and guest materials. TPBi was used as exciton protection material. The dependences of the MEH-PPV concentrations into the PFO (PFO:MEH-PPV) on the optical and electrical properties of the WPLEDs were investigated. The effect of the introduction of TPBi layer was studied by means of the property comparison between the samples with and without TPBi layer. The maximum luminance with 1480 cd/m2 was obtained at the MEH-PPV concentration of 1.0 wt.% for the ITO/PEDOT:PSS/PFO:MEH-PPV/LiF/Al structure. In addition, the maximum luminance and current efficiency of the WPLED with TPBi layer were 7560 cd/m2 at 12 V and 7.8 cd/A at 10 cd/m2, respectively. The CIE color coordinates for WPLED with 1.0 wt.% MEH-PPV concentration was found to be (x, y) = (0.36, 0.33), showing pure white color.