Further, four doped films of 1.5 wt% 4CzTPNBu: TCP-BP-SFAC (15 nm) (film I), 1 wt% DBP: TCP-BP-SFAC (9 nm)/1.5 wt% 4CzTPNBu: TCP-BP-SFAC (5 nm) (film II), 1 wt% DBP: TCP-BP-SFAC (15 nm) (film III), and TCP-BP-SFAC (15 nm) (film IV) are prepared to study the sensitization process. As illustrated in Fig. , the PL peaks of TCP-BP-SFAC, 4CzTPNBu and DBP are located at 480, 550 and 610 nm, respectively, which are consistent with their intrinsic PL properties. The transient PL decay curves detected at these PL peaks reveal that film IV has the longest decay lifetime at 480 nm (Fig. and Supplementary Table ). The mechanism of exciton behaviors is depicted in Fig. . The TADF dopant 4CzTPNBu has lower lying S1 and T1 states than TCP-BP-SFAC, which can induce exciton diffusion towards 4CzTPNBu, thus leading to reduced delayed lifetime of TCP-BP-SFAC in film I. Film II contains red and orange layers with the identical configuration to that of white EML in W2-1. The delayed lifetime of film II at 550 nm is shortened relative to that of film I. Meanwhile, conventional fluorescence dopant DBP has a considerable decay lifetime at the scale of 20 μs, much longer than that in toluene solution, evidencing efficient FET from 4CzTPNBu to DBP. This is also supported by their overlapped absorption and PL spectra (Fig. ). In film III, TCP-BP-SFAC exhibits the shortest delayed lifetime, and DBP has the reduced delayed lifetime as well, reflecting non-radiative process dominates in film III due to the Dexter energy transfer between T1 states from TCP-BP-SFAC to DBP. These findings manifest that the FET occurs between DBP and 4CzTPNBu but not between DBP and TCP-BP-SFAC.