LAUSR

In this work, the multilayer organic light emitting transistors (OLETs) based on high‐k polymer crosslinked poly(vinyl alcohol) (C‐PVA) as the dielectric layer are studied. The devices show an excellent brightness of 14 500 cd m−2 and a record breaking external quantum efficiency (EQE) of about 9.0% in inert atmosphere. The use of perfluoro(1‐butenyl vinyl ether) polymer (CYTOP) modified C‐PVA as a hydrophobic dielectric affords OLETs with good stability, displaying a maximum brightness of 13 400 cd m−2 and EQE of 7.31% in ambient conditions with high humidity (relative humidity RH = 70%). Furthermore, the flexible OLETs based on CYTOP/C‐PVA dielectric layer show a brightness of 8300 cd m−2 and a peak EQE at 9.01%, which is the first reported flexible OLET with >500 cd m−2 brightness. The excellent OLET device performance is ascribed to the excellent hole transport structure, high efficiency of guest–host system, and the better carrier balance in the emitting layer, which could be a practical strategy to develop high‐performance flexible OLETs. It is proven for the first time that OLETs could achieve such high EQE and brightness, even for flexible OLETs, paving the way for their future application in industry.