High‐Performance Narrowband Blue OLEDs With Enhanced Efficiency and Stability by Leveraging Single‐Crystalline Hole Transport Layers

The development of high‐performance blue OLEDs with narrowband emission, high efficiency, and high stability is crucial for ultrahigh‐definition displays. The limitations of amorphous films, notably their low carrier mobility and inherent instability, pose significant impediments to the development of OLED technology. To address this challenge, a p ‐type organic single crystal (SC) of 3PV‐Me with favorable crystalline and optoelectronic properties was introduced in the OLEDs (SC‐OLEDs) as the hole transport layer (HTL) in combination with an emissive layer (EML) consisting of a triplet‐triplet up‐conversion (TTU) host doped with multi‐resonant thermally activated delayed fluorescence (MR‐TADF) blue emitters. Through a systematic investigation, 3PV‐Me SC‐HTLs are demonstrated to exhibit superior interfacial characteristics at both the SC‐HTL/EML and SC‐HTL/electrode interfaces, thereby facilitating highly ordered crystallinity of the EML with a higher horizontal dipole ratio. Benefiting from these advantages, the fabricated SC‐OLEDs achieve a pure‐blue emission with a full width at half maximum (FWHM) of only 23 nm and a y color coordinate below 0.07, alongside a high external quantum efficiency (EQE) exceeding 10.02%, and long operational lifetime (LT 50 > 1076 h). These findings highlight the significant potential of the SC‐HTL strategy for realizing efficient and stable blue OLEDs with high color purity.