In our previous work, we investigated the effects of the formation of ultrastable glasses within monochrome phosphorescent organic light-emitting diodes.1 The ultrastable glasses are fabricated by heating the glass substrate to about 85% of the glass transition temperature while evaporation of the material We observed significant enhancements of the external quantum efficiency fin the range of 20%) and device lifetime (up to 4x). These improvements are attributed to a denser packaging of the organic molecules resulting in reduced non-radiative rates of the emitters. The change in the nano-morphology can also have impact on the charge transport, the radiative rates of the emitter, and emitter orientation. For those properties, we have not identified a significant impact on the device performance. In this paper, we apply our concept to a green thermally activated delayed fluorescent emitter in a proof of principle device series. We find that insufficient energy transfer to the emitter holds back our devices from achieving state-of-the-art efficiencies.