Two phenanthro[9,10-d]imidazole (PI) derivatives, DPAA-PPI and tBuDPAA-PPI, were synthesized. The non-doped OLEDs with DPAA-PPI and tBuDPAA-PPI as emitters displayed very low driving voltages, high brightness and maximum external quantum efficiencies (EQE) of 5.2% and 4.1%, respectively.