Enhancement of PtOEP phosphorescence using graphene quantum dots as host materials

Abstract

OLED arises as leading technologies in the display industry, however, expensive fabrication processes and lack of color purity are not yet been resolved. In order to realize pure color emission layer with low cost, not only solution processes but cheap host material need to be developed. Graphene, due to its abundant $sp^2$ carbons, has been reported to show good compatibility with $\pi$-conjugated dopants, but zero bandgap characteristic of graphene, makes it strong acceptor rather than donor which hindered its application as a host material. In this study, we fabricated cost-effective deep-red color emission layer realized by PEG-GQD:PtOEP host-dopant system. Spectral overlap between PEG-GQD PL and PtOEP absorbance was observed to expect that FRET and DET from PEG-GQD can be possible. As-synthesized PEG-GQD:PtOEP (50 wt%) complexes shows enhancement in phosphorescence intensity by 1.2-fold comparing to PtOEP only. Obtained 52.21% PL-QY was by far the highest PL-QY values in solution phase ever reported. PtOEP PL lifetime was increased by doped into PEG-GQDs both in room temperature and 77K, revealing that there were efficient FRET and DET occurred from PEG-GQD to PtOEP. GQDs with increasing oxidation degree shows decrease in phosphorescence, which resulted from stable singlet and triplet levels of (R)GOQDs and reduced $\pi$-$\pi$ interactions that cause energy back transfer to (R)GOQD hosts, and poor confinement of excitons in PtOEP. Spin-coated PEG-GQD:PtOEP emissive films were fabricated by showing similar enhancement and color purity, which can be used as OLED emission layer.