Enhancing Phosphorescence through Rigidifying the Conformation to Achieve High-Efficiency OLEDs by Modified PEDOT.

Bis(diphenylphosphinomethyl)phenylphosphine (dpmp)-supported PtAu heterotrinuclear complexes [PtAu(dpmp)(C≡CPh)](ClO) (), [PtAu(dpmp)(DEBf)(C≡CPh)](ClO) (), and [PtAu(dpmp)(DECz)(C≡CPh)](ClO) () were prepared and used in organic light-emitting diodes (OLEDs) as a new class of light emitters, where DEBf = dibenzofuran-4,6-diacetylide and DECz = 3,6-di--butylcarbazole-1,8-diacetylide. Although the flexible structure of PtAu complex (λ = 503 nm, Φ < 0.1%) results in weak photoluminescence in fluid CHCl, complexes (λ = 585 nm, Φ = 4.9%) and (λ = 589 nm, Φ = 3.2%) with a rigid conformation give a much stronger phosphorescence. The displacement of two σ-bonded phenylacetylide ligands with a diacetylide ligand such as DEBf and DECz to fasten PtAu structures facilitates greatly luminescent emission so that the emissive quantum yield in doping film is as high as 89% for and 93% for . As revealed by a theoretical study, the severe structural distortion of diacetylide-linked PtAu complexes (λ = 585 nm) and (λ = 589 nm) in a triplet excited state gives rise to significant red shifts of phosphorescent emission spectra relative to that of complex (λ = 503 nm). By means of PtAu complexes as phosphorescent emitters, solution-processed OLEDs achieved a relatively low external quantum efficiency (EQE < 9.5%) when commercial poly(ethylenedioxythiophene):poly(styrenesulfonic acid) (PEDOT:PSS) was used as the hole-injection layer (HIL). In contrast, the peak EQE was increased to 18.3% with a dramatic increase of efficiency by the use of modified HILs composed of PEDOT:PSS and PSS-Na, which provide a higher work function and a better film morphology.