FLOW-INDUCED ALIGNMENT OF SEMICONDUCTOR NANORODS FOR HIGH OUTCOUPLING-FACTOR LIGHT-EMITTING DEVICES

Abstract

The alignment of anisotropic semiconductor nanocrystals in the film poses important challenges for improved overall efficiency of electroluminescent devices [1]. The horizontal dipole orientation of the emitters on the substrate immediately enhance the optical extraction efficiency of the device. Herein, we report the degree of alignment of CdSe/CdS core/shell dot-in-rods (DIRs) concerning the coating direction in the emissive film by monitored locally using the polarized optical microscopy. The capillary tube system, which strictly confine the evaporation rate by the vapor pressure of a solvent [2], provides a quantified insight into the arrangement of quantum nanorods according to the flow rate in the film forming. DIRs film showed that the alignment increased in the in-plane direction in proportion to the coating velocity. In particular, a conductive polymer with massive molecular weight such as poly(9-vinylcarbazole) (PVK) determined the orientation direction according to the initial film formation rate and this orientation was maintained in the capillary deposition. This study on flow-induced alignment of anisotropic nanocrystals provides quantitative understandings in the solution processible film formation, which expands to prerequisites that can be directly used for inkjet printing, a commercially promising next-generation film forming techniques.