where γ represents the charge carrier balance factor, which is typically assumed to be close to unity. The effective radiative efficiency ηeff is given by the ϕ of the solid film, as determined above (cf. Table ). As the pyrene-based emitters are dispersed in a CBP matrix, we expect an isotropic dipole orientation. To corroborate this claim, we perform angle-resolved photoluminescence spectroscopy and determine the vertical isotropy factor to be at α = 0.32 for PyPhCz and α = 0.30 for PyFlCz. Both results are very close to 0.33, therefore representing almost perfect isotropic dipole orientation (α = 1, would indicate complete vertical orientation) (see Figure ). This analysis gives us confidence in treating the outcoupling efficiency ηout to be close to 0.2. For purely fluorescent OLEDs, the spin factor ηST is limited to 0.25, while ηST can reach up to 1 for triplet-harvesting devices. For our OLEDs, we determine limited EQEs of 4.19 % for PyPhCz and 4.45 % for PyFlCz for the case where no triplet states were involved.