Investigation of charge-transport properties in polymer/fullerene blends using transient electroluminescence technique

Abstract

The charge-transport property is one of crucial factors to determine the performance of the polymer-based devices. The hole-transport properties of regioregular poly(3-hexylthiophene-2,5diyl) (P3HT) and [6,6]-phenyl C61-butyric acid methyl ester (PCBM) blends with two blend ratios were investigated using transient electroluminescence (EL) measurements. For EL, organic light emitting diodes are fabricated with P3HT:PCBM blends as hole-transport layers. To reduce absorption, a red phosphorescent emitter with bis(1-phenylisoquinolinato-N,C2′) iridium(acetylacetonate) [(piq)2Ir(acac)] was used. Transient EL with red color is obtained in spite of P3HT:PCBM absorption and hole mobilities of P3HT:PCBM layers are calculated using delay times in transient EL signals. The hole mobility of pristine P3HT:PCBM with 1:0.8 blend ratio is approximately 6.2 × 10−5 cm2 V−1 · s−1 at approximately 615 kV cm−1, and it decreases when the PCBM ratio increases. The hole mobility of the P3HT:PCBM layer increases to approximately 1.07 × 10−4 cm2 V−1 · s−1 at approximately 615 kV cm−1 when the P3HT:PCBM blend is thermally annealed.