Suppressing thermal quenching via defect passivation for efficient quasi-2D perovskite light-emitting diodes

Emission thermal quenching is commonly observed in quasi-2D perovskite emitters,which causes the severe drop in luminescence eficiency for the quasi-2D perovskite light-emitting diodes(Pel EDs)during practical operations.However,this issue is often neglected and rarely studied,and the root cause of the thermal quenching has not been completely revealed now.Here,we develop a passivation strategy via the 2,7-dibromo-9,9-bis(3'-diethoxylphosphorylpropyl-fluorene to investigate and suppress the thermal quenching.The agent can effectively passivate coordination-unsaturated Pb2+defects of both surface and bulk of the flm without affecting the perovskite crysaliation,which helps to more truly demonstrate the important role of defects in thermal quenching.And our results reveal the root cause that the quenching will be strengthened by the defect promoted exciton-phonon coupling.Ultimately,the PeL EDs with defect passivation achieve an improved external quantum efficiengy(EQE)over 22%and doubled operation lifetime at room temperature,and can maintain about 85%of the initial EQE at 85℃,much higher than 17%of the control device.These findings provide an important basis for fabricating practical PeLEDs for lighting and displays.

Carbazole ring: A delicate rack for constructing thermally activated delayed fluorescent compounds with through-space charge transfer

Three carbazole derivatives, Ac PTC, Px PTC and Pt PTC, consisting of two 9,9-dimethyl-9,10-dihydroacridine,phenoxazine or phenothiazine donor groups and one diphenyltriazine acceptor group fixed at 1,8,9-positions of a single carbazole ring via phenylene, are designed and synthesized. X-ray diffraction analysis of Ac PTC reveals that there exist multiple π-π interactions between the donor and acceptor groups to form a sandwich-like structural unit with edge-to-face interaction model. The compounds thus show obvious thermally activated delayed fluorescence with through-space charge transfer character and possess considerable photoluminescence quantum yields of up to 73% in doped films with sky-blue to yellow emissions. The solution-processed electroluminescent devices achieve the highest maximum external quantum efficiencies of 10.0%, 11% and 5.6% for Ac PTC, Px PTC and Pt PTC, respectively, with small efficiency roll-offs.