Moreover, an orange fluorescence emitter TBRB is used as detector to study the FET process in the device (Fig. ). The absorption spectrum of TBRB is finely overlapped with the PL spectrum of TCP-BP-SFAC (Fig. ), indicating sufficient FET can happen from TCP-BP-SFAC to TBRB. An ultrathin (0.2 nm) layer of TBRB neat film is inserted into the TCP-BP-SFAC layer at varied positions, and the relative emission intensity of TBRB/TCP-BP-SFAC is recorded to draw the relative intensity-position-voltage graph (Fig. ). It is found that the exciton recombination zone tends to locate near the hole-transporting part at low voltages, but is more evenly distributed over the entire EML at high voltages. Therefore, it is deduced that the electrons can arrive at 4CzTPNBu at low voltages with partial recombination in TCP-BP-SFAC layer, and shift towards another TCP-BP-SFAC layer through 4CzTPNBu when the operating voltage is increased, leading to enhanced blue component in white light. So, the