Hence to reduce efficiency roll-off, we need to reduce triplet lifetime -or more precisely, the triplet population during device operation. The key photophysical processes in a TADF emitter are shown in Fig. . Singlets are converted to triplets with rate constant kISC; and triplets to singlets at rate constant kRISC. There is potentially radiative and non-radiative decay of both triplets and singlets, though in a good TADF material 𝑘 ! " will be much larger than any of 𝑘 #! " , 𝑘 ! $ and 𝑘 #! $ 20,21 . The main approach advocated in the literature for reducing efficiency roll-off is to increase kRISC, commonly by reducing ∆EST through molecular design by reducing the exchange integral between the HOMO and LUMO. In addition, there have been other attempts to increase kRISC, for example by the use of heavy atoms, to increase spin-orbit coupling (SOC) . The emphasis on kRISC is so strong that in the past 6 years, there have been 16 publications in the Nature family alone exploring kRISC . However, the expected improvement in J90 has not always materialised.