No abstract

The mobility of charge carriers has been investigated in the pristine and phosphorescent material doped 4 , 4Ј ,4Љ-tris͑N-carbazolyl͒ triphenylamine ͑TCTA͒ using time-of-flight photoconductivity technique. Doping phosphorescent material fac-tris͑2-phenylpyridine͒ iridium ͓Ir͑ppy͒ 3 ͔ increases the electron mobility whereas the hole mobility decreases to the order of 10 −4-10 −6 cm 2 / V s measured at room temperature with different bias voltages. The analysis of field and temperature dependences of the mobility agrees well with the Gaussian disorder model. The calculated positional disorders ͑⌺͒ for TCTA, Ir͑ppy͒ 3-doped TCTA, and tris͑1-phenylisoquinoline͒ iridium ͓Ir͑piq͒ 3 ͔-doped TCTA are 0.12, 2.05, and 1.62 for hole, respectively; 3.89 for electron in only Ir͑ppy͒ 3-doped TCTA. The ambipolar transport for holes and electrons is possible by doping TCTA with Ir͑ppy͒ 3 ͑green dopant͒ whereas only hole transport with reduced mobility is achieved for Ir͑piq͒ 3 ͑red dopant͒.

No abstract

No abstract

The effect of a nanoscale boron subphthalocyanine chloride (SubPc) interfacial layer on the performance of inverted polymer solar cells based on poly (3-hexyl thiophene) (P3HT) and [6,6]-phenyl-C(71)-butyric acid methyl ester (PC(71)BM) was studied. When a 1 nm SubPc layer was introduced between the active layer (P3HT:PC(71)BM) and MoO(x) in the device with ITO/ZnO/P3HT:PC(71)BM/SubPc/MoO(x)/Al configuration, the power conversion efficiency (PCE) was increased from 3.42 (without SubPc) to 3.59%. This improvement is mainly attributed to the enhanced open-circuit voltage from 0.62 to 0.64 V. When the Flory-Huggins interaction parameters were estimated from the solubility parameters through the contact angle measurement, it revealed that the interaction between SubPc and PC(71)BM is more attractive than that between SubPc and P3HT at the interface of P3HT:PC(71)BM/SubPc, through which charges are well transported from the active layer to the anode. This is supported by a decrease of the contact resistance from 5.49 (SubPc 0 nm) to 0.94 MΩ cm (SubPc 1 nm). The photoelectron spectra provide another evidence for the enhanced PCE, exhibiting that the 1 nm thick SubPc layer extracts more photoelectrons from the active layer than other thicknesses.