Efficient Organic Light-Emitting Diodes Based on Ambipolar Doped Organic Single Crystals of Bis-Styrylbenzene Derivatives

Ambipolar carrier transport in organic single crystals is essential to maximize exciton recombination and thus achieve high-efficiency organic light-emitting diodes (OLEDs). Herein, two bis-styrylbenzene derivatives, 1,4-bis(4-methylstyryl)benzene (3PV-Me) and 1,4-bis(4-trifluoromethylstyryl)benzene (3PV-CF₃), are introduced into the construction of ambipolar 3PV-CF₃ doped 3PV-Me (3PV-Me-CF₃) single crystals. The same molecular skeleton of these two molecules endow them with similar molecular shapes and sublimation temperatures. Doping with 3PV-CF₃ dopants is evaluated for their effect on the photophysical properties of host 3PV-Me crystal. Systematic spectroscopic investigations and high-resolution time-of-flight secondary ion mass spectrometry (TOF-SIMS) depth profiling are further conducted to gain a deep insight into the doping details of 3PV-Me-CF₃ single crystals. Furthermore, their ambipolar carrier transport behavior is evaluated by the space-charge-limited current (SCLC) method, exhibiting nearly equal hole and electron mobilities. These ambipolar 3PV-Me-CF₃ single crystals are then utilized for the fabrication of single-crystal OLEDs, which demonstrated an almost sixfold enhancement in the electroluminescence (EL) efficiency in comparison to the unipolar 3PV-Me single-crystal OLEDs. The findings reveal the great potential of well-balanced ambipolar organic single-crystalline semiconductors for the development of high-performance single-crystal optoelectronic devices.