Isolated asymmetric bilateral steric conjugated polymers with thickness-independent emission for efficient and stable light-emitting optoelectronic devices

Abstract

Isolating the mainchain of light-emitting conjugated polymers (LCPs) is an effective strategy to obtain ultrastable efficient deep-blue light-emitting devices for printed optoelectronics. Herein, considering the complicated excitonic behavior that is induced by an uncontrollable film morphology, we proposed a novel asymmetric bilateral steric (ABS) strategy to construct a highly steric wide bandgap LCP (PHPDPF-Cz) via suppressing the formation of the interchain excited state toward efficient organic lasers and deep-blue polymer light-emitting diodes (PLEDs). Two large steric biphenyl (∼1.0 nm) and carbazole (Cz) molecules are introduced into the mainchain asymmetrically localized at the 9- and 4-position to effectively suppress interchain interaction at the molecular level and achieve single-chain excitonic behavior. PHPDPF-Cz shows ultrastable deep-blue emission upon thermal annealing, air aging, and increasing film thickness, with respect to the controlled polymer. Therefore, our PHPDPF-Cz presents an excellent thermal-stable deep-blue lasing behavior with a low threshold of ∼2 μJ cm⁻². Finally, efficient and stable deep-blue preliminary PLEDs are fabricated with single-molecule excitonic behavior, which present thickness-independent (80 nm to 250 nm) electroluminescence (EL) properties with a high current efficiency (C.E.) and external quantum efficiency (EQE) of 2.11 cd A⁻¹ and 1.78%, respectively. Obviously, the morphology-independent efficient and stable EL behaviour is desirable for improving device reproducibility and stability, indicating their potential application in printed optoelectronics.