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Organic single crystals have a great potential in the field of organic optoelectronics because of their advantages of high carrier mobility and high thermal stability. However, the application of the organic single crystals in light-emitting devices (OLEDs) has been limited by single-layered structure with unbalanced carrier injection and transport. Here, fabrication of a multilayered-structure crystal-based OLED constitutes a major step toward balanced carrier injection and transport by introducing an anodic buffer layer and electron transport layer into the device structure. Three primary color single-crystal-based OLEDs based on the multilayered structure and molecular doping exhibit a maximum luminance and current efficiency of 820 cd cm−2 and 0.9 cd A−1, respectively, which are the highest performance to date for organic single-crystal-based OLEDs. This work paves the way toward high-performance organic optoelectronic devices based on the organic single crystals. [ABSTRACT FROM AUTHOR]

Organic single crystals with much higher carrier mobility and stability compared to the amorphous organic materials have shown great potential in electronic and optoelectronic devices. However, their applications in white organic light‐emitting devices (WOLEDs), especially the three‐color‐strategy WOLEDs, have been hindered by the difficulties in fabricating complicated device structures. Here, double‐doped white‐emission organic single crystals are used as the active layers for the first time in the three‐color‐strategy WOLEDs by co‐doping the red and green dopants into blue host crystals. Precise control of the dopant concentration in the double‐doped crystals results in moderately partial energy transfer from the blue donor to the green and red dopants, and thereafter, simultaneous RGB emissions with balanced emission intensity. The highest color‐rendering index (CRI) and efficiency, to the best of the authors' knowledge, are obtained for the crystal‐based WOLEDs. The CRI of the WOLEDs varies between 80 and 89 with the increase of the driving current, and the luminance and current efficiency reach up to 793 cd m−2 and 0.89 cd A−1, respectively. The demonstration of the present three‐color organic single‐crystal‐based WOLED promotes the development of the single crystals in optoelectronics. High‐color‐rendering and high‐efficiency three‐color‐strategy white organic light‐emitting devices (WOLEDs) are realized using double‐doped white‐emission organic single crystals, which are grown by co‐doping red and green dopants into the blue host. The crystal‐based WOLEDs exhibit the maximum luminance, current efficiency, and external quantum efficiency of 793 cd m−2, 0.89 cd A−1, and 0.48%, respectively, which promote the development of the organic single crystals in optoelectronics. [ABSTRACT FROM AUTHOR]

The transfer-free fabrication of the high quality graphene on the metallic nanostructures, which is highly desirable for device applications, remains a challenge. Here, we develop the transfer-free method by direct chemical vapor deposition of the graphene layers on copper (Cu) nanoparticles (NPs) to realize the hybrid nanostructures. The graphene as-grown on the Cu NPs permits full electric contact and strong interactions, which results in a strong localization of the field at the graphene/copper interface. An enhanced intensity of the localized surface plasmon resonances (LSPRs) supported by the hybrid nanostructures can be obtained, which induces a much enhanced fluorescent intensity from the dye coated hybrid nanostructures. Moreover, the graphene sheets covering completely and uniformly on the Cu NPs act as a passivation layer to protect the underlying metal surface from air oxidation. As a result, the stability of the LSPRs for the hybrid nanostructures is much enhanced compared to that of the bare Cu NPs. The transfer-free hybrid nanostructures with enhanced intensity and stability of the LSPRs will enable their much broader applications in photonics and optoelectronics. [ABSTRACT FROM AUTHOR]

The transferred chemical vapor deposition (CVD)-grown graphene from copper foils to other desired substrates by using poly(methyl methacrylate) (PMMA) as supporter, suffers from problems of rough surface, low conductivity and poor wettability, which hinders its applications in optoelectronic devices. In this work, a combined thermal annealing and HNO 3 doping treatment for graphene electrode has been employed to simultaneously improve its smoothness, conductivity and wettability. The thermal annealing process results in the improved surface smoothness by removing the PMMA residue. HNO 3 doping treatment for the graphene enhances its conductivity and surface wetting to PEDOT:PSS. Furthermore, the work function (WF) of two-step treated graphene increased from ∼4.4 eV to ∼5.1 eV. Small-molecule organic solar cells (OSCs) based on the two-step treated graphene anodes exhibit a power conversion efficiency (PCE) of 2.43%, which is comparable to that of ITO electrode (2.48%). This work demonstrates the bright future of graphene transparent electrodes as a replacement for ITO. [ABSTRACT FROM AUTHOR]