Abstract
The performance of solution‐processed organic light‐emitting diodes (OLEDs) based on thermally activated delayed fluorescent (TADF) emitter of 3,4,5,6‐tetrakis (carbazol‐9‐yl)‐1, 2‐dicyanobenzene (4CzPN) is optimized via adjusting the carrier transport layer. The device with 1,3,5‐Tris(1‐phenyl‐1Hbenzimidazol‐2‐yl) benzene (TPBi) as electron transport layer (ETL) demonstrates much higher efficiency compared to the device with 1, 3, 5‐Tri [(3‐pyridyl)‐phen‐3‐yl] benzene (TmPyPB) as ETL. The proposed mechanism is that triplet‐charge annihilation is alleviated since fewer holes are accumulated at the interface between the emission layer (EML) and ETL due to lower lying highest occupied molecular orbital (HOMO) of TPBi. In addition, the hole transport material of (N,N′‐bis (3‐methylphenyl)‐N,N′‐bis (phenyl)‐benzidine) (TPD) inserted at the PEDOT:PSS/EML interface could block electron leakage and suppress the exciton quenching by PEDOT:PSS. And thus, the device efficiency is improved. The current efficiency of 18.46 cd A−1 and external quantum efficiency of 5.99% are achieved for the solution‐processed 4CzPN‐based device with TPBi as ETL and TPD as hole transport layer (HTL). It is illuminated that suppressing exciton quenching via manipulating carrier behaviors in the EML is an efficient approach for fulfilling high‐performance solution‐processed TADF devices.
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