Vacuum‐Sublimed Cocrystalline Thin Films of Naphthalene Bisimide and Pt(II) Complex for Phosphorescent Light‐Emitting Diodes

Abstract Cocrystals employing small organic molecules with platinum(II)‐complexes are known to exhibit organic room‐temperature phosphorescence (RTP). However, this desirable property is so far only demonstrated in the macroscopic 1:1 cocrystalline state, which limits device applications outside of small single‐crystal devices. Here, this work shows that vacuum cosublimed thin films of both components in various mixing ratios form layers with self‐assembled small cocrystalline domains which exhibit RTP. This Pt(II) doping improves the photoluminescence (PL) quantum yield ( Φ PL ) of the now phosphorescence emitting 1,8:4,5‐naphthalene bisimide (NBI) from below 0.1% to 9% in respective thin films. These doped layers are employed as active layers in light‐emitting diodes to emit red electroluminescence (EL). Via time‐resolved measurements the lifetime of the device EL is determined in accordance with the PL to be around 50 µs. Maximum external quantum efficiencies ( EQE s) of over 0.2% with RTP emission signatures consistent with the PL of solution‐grown cocrystals could be achieved.