Tetradentate Pt(II) complex as a singlet exciton sensitizing host for highly efficient green fluorescent organic light-emitting diodes

Efficient green fluorescent organic light-emitting diodes were designed with a phosphorescent metal complex as a singlet exciton sensitizing host (SESH) for achieving high efficiency and low efficiency roll-off through exciton and polaron management. Tetradentate Pt(II) complex (Pt-Trz) possessing a tetradentate ligand with a bulky blocking group not only suppresses the severe formation of excimer or dimer itself but also transfers radiative excitons to fluorescent dopant effectively. The SESH assisted fluorescence (SESHF) device with Pt-Trz as the host exhibits the maximum external quantum efficiency of 13.3% and a lower efficiency roll-off compared with exciplex host device which is a general approach for harvesting triplet excitons. Numerical exciton dynamics modeling unravels that the SESHF device effectively utilizes triplet excitons in the host by intersystem crossing and resonance energy transfer from the triplet state of the host to the singlet state of the terminal emitter. Bimolecular quenching rates of the SESHF device are reduced by 11 times for triplet-triplet annihilation and 1.8 times for tripletpolaron annihilation compared with the exciplex device, which demonstrates that Pt-Trz could be a platform to be used as an efficient host for fluorophores.