A dual-functional single-crystalline layer boosts operational stability of organic light-emitting diodes

The extreme sensitivity to the environment and inherent instability of organic materials have posed persistent challenges to achieving long-term operational stability of organic light-emitting diodes (OLEDs). Herein, a dual-functional single-crystalline layer of 1,4-bis(4-methylstyryl)benzene (BSB-Me) is introduced into the OLED structure, simultaneously serving as both an intrinsically stable hole-transporting layer (HTL) and an effective barrier layer, to improve device stability. Systematic characterizations are conducted to gain an insight into the stability property of BSB-Me single crystals (SCs), confirming their robust thermal, morphological, and electrochemical stabilities. The SCs also exhibit desirable barrier property with a low water vapor transmission rate (WVTR) of approximately 3.58 × 10^-4 g m^-2 day^-1, which is comparable to that of a 50-nm-thick monolayer Al₂O₃ barrier layer. In consequence, highly efficient and stable single-crystal OLEDs (SC-OLEDs) can be successfully fabricated by introducing the dual-functional BSB-Me SC layer. The blue SC-OLEDs present extended operational lifetimes (LT₇₅) of over 1209 h at an initial luminance of 1000 cd cm^-2, which is notably more than thirty times enhanced compared to that of conventional OLEDs with amorphous HTLs. Our findings suggest that the introduction of a dual-functional single-crystalline layer presents a promising advancement for improving the operational stability of OLEDs.