Synthesis of ZnS Quantum Dots for QDs-LED hybrid device with different cathode materials

Abstract

In this study, a chemical method was used to synthesise ZnS quantum dots (QDs) with low cost and simple process. A fixed molar ratio 1:1 of zinc chloride and sodium sulfide has been used for preparing two samples A and B. The X-ray diffraction (XRD) analyses prove the cubic phase of ZnS with an average particles size of (3-29) nm According to UV-Vis. spectra analyses, a large blue shift over 32 and 48 nm was observed, while the band gaps energy (Eg) were 3.55 and 3.8 eV for A and B samples respectively. The emission spectrum of quantum dots carries more evidence on the presence of shallow at 373 and 367 nm originated from the interstitial Zn and traps at 428 and 439 nm, whose origin ascribed to defects zinc vacancy (VZn), while 541 nm was due to sulfide vacancy (VS). QDs-LED hybrid devices were fabricated using ITO/PEDOT: PSS/Poly-TPD/ZnS-QDs/layers with two types of cathode materials LiF and Al. Using LiF as cathode in addition to the Al gives good enhancement to light generation in compares with that of Al cathode only. The spectra 350-700 nm appeared a wide emission band according to the EL measurement.