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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]

Fe3O4 has been demonstrated to be an efficient p-dopant in improving the performance of organic light-emitting devices. This paper investigates in detail the role of Fe3O4 in improving the hole injection and the hole transport by the ultraviolet/visible/near-infrared absorption, x-ray, and ultraviolet photoelectron spectroscopy. The results demonstrated that Fe3O4 as a p-dopant has different effectiveness when it is doped into different host materials. The improved properties of the OLEDs with the p-doped N, N'-diphenyl-N,N'-bis (1,1'-biphenyl)-4,4'-diamine layer is mainly due to the enhanced hole injection through the lowering of the hole injection barrier, while the enhanced hole transport plays a more important role for the OLEDs with the p-doped 4,4',4”-tris (3-methylphenylphenylamino) triphenylamine due to their higher ability in the formation of charge transfer complex. [ABSTRACT FROM PUBLISHER]

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]

Abstract: In this work, large-size tetracene- and pentacene-doped 1,4-Bis(4-methylstyryl)-benzene (BSB-Me) crystals were prepared with physical vapor transfer technique. The photoluminescence emission can be adjusted from blue to green and even to red by changing the doping. Their fluorescence features are investigated by both the steady-state fluorescence spectra and time-resolved fluorescence measurements, which indicate highly efficient energy transfer from the host BSB-Me to the acceptor. The PL efficiencies of the tetracene-doped BSB-Me and pentacene-doped BSB-Me crystals are as high as 79% and 47%, the energy transfer efficiency is 49.7% and 73.1%, respectively. Excitation intensity-dependent ultrafast dynamics was further probed, which shows that the kinetics in doped crystals exhibit much less excitation intensity dependence than that of the pure BSB-Me crystals. Our results are relevant to the understanding of ultrafast energy-transfer dynamics in doped crystals and are expected to be of interest for organic light emitting transistors, diodes, and lasers. [Copyright &y& Elsevier]

Organic single-crystalline semiconductors have drawn significant attention in the area of organic electronic and optoelectronic devices due to their superiorities of highly ordered structure, high carrier mobility and low impurity content. Molecular doping technique has made great progress in improving device performance via optimizing the optical and electrical properties of organic semiconductors. In particular, this technique has been attempted by taking fluorescent dye-molecules as the emissive dopants to tune emission color and improve device performance of organic single crystals. Up to now, there are few reports about the use of molecular doping in organic single crystals to optimize their intrinsic electrical properties. Here, we have introduced the controllable molecular doping as a feasible approach toward manipulating charge carrier transport properties of organic single crystals. Upon optimization of doping concentration, balanced carrier transport can be realized in 5,5′-bis(4-trifluoromethyl phenyl) [2,2'] bithiophene (P2TCF 3)-doped 1,4-bis(4-methylstyryl) benzene (BSB–Me) crystals. Organic light-emitting devices (OLEDs) based on these doped crystals achieve a maximum luminance of 423 cd/m2 and current efficiency of 0.48 cd/A. It demonstrates that high-efficiency crystal-based OLEDs are of great significance for the development of organic electronics, especially for display and lighting applications. Image 1 • The n -type P2TCF 3 has been introduced as dopant into a p -type BSB-Me host crystal. • Molecular doping is employed for realizing balanced carrier transport. • The comparable hole and electron mobilities can be obtained in doped crystals. • The luminance of doped crystal-based OLEDs is 3.5 times that of undoped crystal. • The current efficiency is correspondingly increased by 3.2 times. [ABSTRACT FROM AUTHOR]