Fabrication of high efficient organic/CdSe quantum dots hybrid OLEDs by spin-coating method

Abstract

The cadmium selenite (CdSe) quantum dots (QDs) have promising applications in display technology since its luminescence wavelength can be tuned precisely from blue to red by changing the diameter of the core from 2.0 to 7.0 nm. A self-assembled monolayer of QDs, sandwiched between two organic thin films is necessary to isolate the luminescence processes from charge conduction. The use of QDs for device technology, one of the fundamental issues is how to distribute QDs uniformly on patterned surfaces with precise control of density. In this study, we demonstrate that uniform distribution of QDs with controllable density can be achieved using the conventional spin-coating method. We have fabricated high efficient QD-OLED by spin-coating method. The estimated QDs threshold concentration was found ~ 9x10 11 cm -2 for the best performance of QD-OLED. The AFM morphological studies of the hybrid device showed the formation of a disordered QD film as a result of the aggregation of CdSe/ZnS QDs upon phase segregation. The analysis of electroluminescence (EL) and photoluminescence (PL) performance of OLED showed that precise control of the QD concentration is necessary to maximize the coverage of QDs on organic surface which is an important factor in color tuning. The peak energies of the EL and PL showed only small spectral shifts and no significant dependence on the QDconcentration. The QD emission was increased about three times by annealing of QD-OLED.