Suppression of external quantum efficiency rolloff in organic light emitting diodes by scavenging triplet excitons

Abstract

Large external quantum efficiency rolloff at high current densities in organic light-emitting diodes (OLEDs) is frequently caused by the quenching of radiative singlet excitons by long-lived triplet excitons [singlet–triplet annihilation (STA)]. In this study, we adopted a triplet scavenging strategy to overcome the aforementioned STA issue. To construct a model system for the triplet scavenging, we selected 2,6-dicyano-1,1-diphenyl-λ5σ4-phosphinine (DCNP) as the emitter and 4,4′-bis[(N-carbazole)styryl]biphenyl (BSBCz) as the host material by considering their singlet and triplet energy levels. In this system, the DCNP’s triplets are effectively scavenged by BSBCz while the DCNP’s singlets are intact, resulting in the suppressed STA under electrical excitation. Therefore, OLEDs with a 1 wt.%-DCNP-doped BSBCz emitting layer demonstrated the greatly suppressed efficiency rolloff even at higher current densities. This finding favourably provides the advanced light-emitting performance for OLEDs and organic semiconductor laser diodes from the aspect of the suppressed efficiency rolloff.

Comparison of different organic solvents used in the luminescent material for OLED devices

“…Assembly of a basic OLED device uses a organic material as luminescent layer on the anode and cathode on top, but this simple structure offers insignificant luminance and elevated threshold voltage. Then, in the literature there are other structures of devices involving more than three multilayers that offer better performance to the OLED devices [21][22][23] . For example, structures containing five layers have been studied and presented good results as electrical and optical performance using the materials 24-26 : • Substrate: rigid material used to support the multilayers of the OLED device.…”

Activating Room-Temperature Phosphorescence of Organic Luminophores via External Heavy-Atom Effect and Rigidity of Ionic Polymer Matrix

“…Compared with fluorescent materials, materials with room-temperature phosphorescence (RTP) have received special attention for their larger Stokes shift and longer lifetime (6)(7)(8)(9)(10)(11)(12)(13). These advantages promote their applications in the fields such as molecular switches (14)(15)(16)(17)(18), organic light-emitting diodes (OLEDs) (19)(20)(21)(22)(23), anticounterfeiting (24) and bioimaging (25). As pure organic molecules typically emit phosphorescence only at low temperature (e.g., 77 K) and under inert conditions (26,27), traditional phosphorescent materials focus on inorganic and organometallic systems (28,29), which normally rely on noble metals like iridium and platinum to promote the intersystem crossing (ISC) process.…”

Activating Room-Temperature Phosphorescence of Organic Luminophores via External Heavy-Atom Effect and Rigidity of Ionic Polymer Matrix

“…Compared with fluorescent materials, materials with room-temperature phosphorescence (RTP) have received special attention for their larger Stokes shift and longer lifetime (6)(7)(8)(9)(10)(11)(12)(13). These advantages promote their applications in the fields such as molecular switches (14)(15)(16)(17)(18), organic light-emitting diodes (OLEDs) (19)(20)(21)(22)(23), anticounterfeiting (24) and bioimaging (25). As pure organic molecules typically emit phosphorescence only at low temperature (e.g., 77 K) and under inert conditions (26,27), traditional phosphorescent materials focus on inorganic and organometallic systems (28,29), which normally rely on noble metals like iridium and platinum to promote the intersystem crossing (ISC) process.…”