Investigation of pure green-colour emission from inorganic-organic hybrid LEDs based on colloidal CdSe/ZnS quantum dots

We studied the operation characteristics of inorganic–organic hybrid light emitting devices (HLEDs) that have a green CdSe/ZnS quantum dot (QD) emitting layer (EML) and a 1,3,5–tris(N–phenylbenzimidazol–2–yl)–benzene (TPBi) hole blocking layer (HBL). A series of devices with a different thickness TPBi HBL all showed pure electroluminescence that is consistent with green photoluminescence of colloidal QDs without any colour contamination from organic layers. The best performance, which we attributed to more balanced charge carrier supply to a QD EML and efficient energy transfer from excitions in a TPBi layer to QDs, was observed from the device with a TPBi HBL of 20 nm thickness: the deep green emission with the luminous efficiency of 1.55 cd/A at standard video brightness (200 cd/m²) and the luminance as large as ~1800 cd/m².